Merge branch 'master' into feature/client_aggs_parsing

buildSrc/src/main/resources/checkstyle_suppressions.xml

@@ -1047,7 +1047,7 @@
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]Discovery.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]DiscoveryModule.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]DiscoverySettings.java" checks="LineLength" />
-  <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]NoneDiscovery.java" checks="LineLength" />
+  <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]TribeDiscovery.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]zen[/\\]ElectMasterService.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]zen[/\\]FaultDetection.java" checks="LineLength" />
   <suppress files="core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]discovery[/\\]zen[/\\]MasterFaultDetection.java" checks="LineLength" />

core/src/main/java/org/elasticsearch/action/admin/cluster/health/TransportClusterHealthAction.java

@@ -194,14 +194,14 @@ public class TransportClusterHealthAction extends TransportMasterNodeReadAction<
     }
 
     private boolean validateRequest(final ClusterHealthRequest request, ClusterState clusterState, final int waitFor) {
-        ClusterHealthResponse response = clusterHealth(request, clusterState, clusterService.numberOfPendingTasks(),
+        ClusterHealthResponse response = clusterHealth(request, clusterState, clusterService.getMasterService().numberOfPendingTasks(),
-                gatewayAllocator.getNumberOfInFlightFetch(), clusterService.getMaxTaskWaitTime());
+                gatewayAllocator.getNumberOfInFlightFetch(), clusterService.getMasterService().getMaxTaskWaitTime());
         return prepareResponse(request, response, clusterState, waitFor);
     }
 
     private ClusterHealthResponse getResponse(final ClusterHealthRequest request, ClusterState clusterState, final int waitFor, boolean timedOut) {
-        ClusterHealthResponse response = clusterHealth(request, clusterState, clusterService.numberOfPendingTasks(),
+        ClusterHealthResponse response = clusterHealth(request, clusterState, clusterService.getMasterService().numberOfPendingTasks(),
-                gatewayAllocator.getNumberOfInFlightFetch(), clusterService.getMaxTaskWaitTime());
+                gatewayAllocator.getNumberOfInFlightFetch(), clusterService.getMasterService().getMaxTaskWaitTime());
         boolean valid = prepareResponse(request, response, clusterState, waitFor);
         assert valid || timedOut;
         // we check for a timeout here since this method might be called from the wait_for_events

core/src/main/java/org/elasticsearch/action/admin/cluster/tasks/TransportPendingClusterTasksAction.java

@@ -65,7 +65,7 @@ public class TransportPendingClusterTasksAction extends TransportMasterNodeReadA
     @Override
     protected void masterOperation(PendingClusterTasksRequest request, ClusterState state, ActionListener<PendingClusterTasksResponse> listener) {
         logger.trace("fetching pending tasks from cluster service");
-        final List<PendingClusterTask> pendingTasks = clusterService.pendingTasks();
+        final List<PendingClusterTask> pendingTasks = clusterService.getMasterService().pendingTasks();
         logger.trace("done fetching pending tasks from cluster service");
         listener.onResponse(new PendingClusterTasksResponse(pendingTasks));
     }

core/src/main/java/org/elasticsearch/action/update/UpdateRequest.java

@@ -98,6 +98,12 @@ public class UpdateRequest extends InstanceShardOperationRequest<UpdateRequest>
     @Override
     public ActionRequestValidationException validate() {
         ActionRequestValidationException validationException = super.validate();
+        if (version != Versions.MATCH_ANY && upsertRequest != null) {
+            validationException = addValidationError("can't provide both upsert request and a version", validationException);
+        }
+        if(upsertRequest != null && upsertRequest.version() != Versions.MATCH_ANY) {
+            validationException = addValidationError("can't provide version in upsert request", validationException);
+        }
         if (type == null) {
             validationException = addValidationError("type is missing", validationException);
         }

core/src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -22,7 +22,6 @@ package org.elasticsearch.cluster;
 import com.carrotsearch.hppc.cursors.IntObjectCursor;
 import com.carrotsearch.hppc.cursors.ObjectCursor;
 import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
-import org.elasticsearch.Version;
 import org.elasticsearch.cluster.block.ClusterBlock;
 import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.metadata.IndexMetaData;

core/src/main/java/org/elasticsearch/cluster/ClusterStateObserver.java

@@ -21,6 +21,7 @@ package org.elasticsearch.cluster;
 
 import org.apache.logging.log4j.Logger;
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.cluster.service.ClusterApplierService;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.unit.TimeValue;
@@ -42,7 +43,7 @@ public class ClusterStateObserver {
 
     private final Predicate<ClusterState> MATCH_ALL_CHANGES_PREDICATE = state -> true;
 
-    private final ClusterService clusterService;
+    private final ClusterApplierService clusterApplierService;
     private final ThreadContext contextHolder;
     volatile TimeValue timeOutValue;
 
@@ -74,7 +75,12 @@ public class ClusterStateObserver {
      */
     public ClusterStateObserver(ClusterState initialState, ClusterService clusterService, @Nullable TimeValue timeout, Logger logger,
                                 ThreadContext contextHolder) {
-        this.clusterService = clusterService;
+        this(initialState, clusterService.getClusterApplierService(), timeout, logger, contextHolder);
+    }
+
+    public ClusterStateObserver(ClusterState initialState, ClusterApplierService clusterApplierService, @Nullable TimeValue timeout,
+                                Logger logger, ThreadContext contextHolder) {
+        this.clusterApplierService = clusterApplierService;
         this.lastObservedState = new AtomicReference<>(new StoredState(initialState));
         this.timeOutValue = timeout;
         if (timeOutValue != null) {
@@ -89,7 +95,7 @@ public class ClusterStateObserver {
         if (observingContext.get() != null) {
             throw new ElasticsearchException("cannot set current cluster state while waiting for a cluster state change");
         }
-        ClusterState clusterState = clusterService.state();
+        ClusterState clusterState = clusterApplierService.state();
         lastObservedState.set(new StoredState(clusterState));
         return clusterState;
     }
@@ -135,7 +141,7 @@ public class ClusterStateObserver {
                     logger.trace("observer timed out. notifying listener. timeout setting [{}], time since start [{}]", timeOutValue, new TimeValue(timeSinceStartMS));
                     // update to latest, in case people want to retry
                     timedOut = true;
-                    lastObservedState.set(new StoredState(clusterService.state()));
+                    lastObservedState.set(new StoredState(clusterApplierService.state()));
                     listener.onTimeout(timeOutValue);
                     return;
                 }
@@ -151,7 +157,7 @@ public class ClusterStateObserver {
 
         // sample a new state. This state maybe *older* than the supplied state if we are called from an applier,
         // which wants to wait for something else to happen
-        ClusterState newState = clusterService.state();
+        ClusterState newState = clusterApplierService.state();
         if (lastObservedState.get().isOlderOrDifferentMaster(newState) && statePredicate.test(newState)) {
             // good enough, let's go.
             logger.trace("observer: sampled state accepted by predicate ({})", newState);
@@ -163,7 +169,7 @@ public class ClusterStateObserver {
             if (!observingContext.compareAndSet(null, context)) {
                 throw new ElasticsearchException("already waiting for a cluster state change");
             }
-            clusterService.addTimeoutListener(timeoutTimeLeftMS == null ? null : new TimeValue(timeoutTimeLeftMS), clusterStateListener);
+            clusterApplierService.addTimeoutListener(timeoutTimeLeftMS == null ? null : new TimeValue(timeoutTimeLeftMS), clusterStateListener);
         }
     }
 
@@ -179,7 +185,7 @@ public class ClusterStateObserver {
             final ClusterState state = event.state();
             if (context.statePredicate.test(state)) {
                 if (observingContext.compareAndSet(context, null)) {
-                    clusterService.removeTimeoutListener(this);
+                    clusterApplierService.removeTimeoutListener(this);
                     logger.trace("observer: accepting cluster state change ({})", state);
                     lastObservedState.set(new StoredState(state));
                     context.listener.onNewClusterState(state);
@@ -198,12 +204,12 @@ public class ClusterStateObserver {
                 // No need to remove listener as it is the responsibility of the thread that set observingContext to null
                 return;
             }
-            ClusterState newState = clusterService.state();
+            ClusterState newState = clusterApplierService.state();
             if (lastObservedState.get().isOlderOrDifferentMaster(newState) && context.statePredicate.test(newState)) {
                 // double check we're still listening
                 if (observingContext.compareAndSet(context, null)) {
                     logger.trace("observer: post adding listener: accepting current cluster state ({})", newState);
-                    clusterService.removeTimeoutListener(this);
+                    clusterApplierService.removeTimeoutListener(this);
                     lastObservedState.set(new StoredState(newState));
                     context.listener.onNewClusterState(newState);
                 } else {
@@ -220,7 +226,7 @@ public class ClusterStateObserver {
 
             if (context != null) {
                 logger.trace("observer: cluster service closed. notifying listener.");
-                clusterService.removeTimeoutListener(this);
+                clusterApplierService.removeTimeoutListener(this);
                 context.listener.onClusterServiceClose();
             }
         }
@@ -229,11 +235,11 @@ public class ClusterStateObserver {
         public void onTimeout(TimeValue timeout) {
             ObservingContext context = observingContext.getAndSet(null);
             if (context != null) {
-                clusterService.removeTimeoutListener(this);
+                clusterApplierService.removeTimeoutListener(this);
                 long timeSinceStartMS = TimeValue.nsecToMSec(System.nanoTime() - startTimeNS);
                 logger.trace("observer: timeout notification from cluster service. timeout setting [{}], time since start [{}]", timeOutValue, new TimeValue(timeSinceStartMS));
                 // update to latest, in case people want to retry
-                lastObservedState.set(new StoredState(clusterService.state()));
+                lastObservedState.set(new StoredState(clusterApplierService.state()));
                 timedOut = true;
                 context.listener.onTimeout(timeOutValue);
             }

core/src/main/java/org/elasticsearch/cluster/ClusterStateTaskExecutor.java

@@ -71,21 +71,18 @@ public interface ClusterStateTaskExecutor<T> {
      * @param <T> the type of the cluster state update task
      */
     class ClusterTasksResult<T> {
-        public final boolean noMaster;
         @Nullable
         public final ClusterState resultingState;
         public final Map<T, TaskResult> executionResults;
 
         /**
          * Construct an execution result instance with a correspondence between the tasks and their execution result
-         * @param noMaster whether this node steps down as master or has lost connection to the master
          * @param resultingState the resulting cluster state
          * @param executionResults the correspondence between tasks and their outcome
          */
-        ClusterTasksResult(boolean noMaster, ClusterState resultingState, Map<T, TaskResult> executionResults) {
+        ClusterTasksResult(ClusterState resultingState, Map<T, TaskResult> executionResults) {
             this.resultingState = resultingState;
             this.executionResults = executionResults;
-            this.noMaster = noMaster;
         }
 
         public static <T> Builder<T> builder() {
@@ -124,11 +121,11 @@ public interface ClusterStateTaskExecutor<T> {
             }
 
             public ClusterTasksResult<T> build(ClusterState resultingState) {
-                return new ClusterTasksResult<>(false, resultingState, executionResults);
+                return new ClusterTasksResult<>(resultingState, executionResults);
             }
 
             ClusterTasksResult<T> build(ClusterTasksResult<T> result, ClusterState previousState) {
-                return new ClusterTasksResult<>(result.noMaster, result.resultingState == null ? previousState : result.resultingState,
+                return new ClusterTasksResult<>(result.resultingState == null ? previousState : result.resultingState,
                     executionResults);
             }
         }

core/src/main/java/org/elasticsearch/cluster/ClusterStateTaskListener.java

@@ -18,6 +18,8 @@
  */
 package org.elasticsearch.cluster;
 
+import org.elasticsearch.cluster.service.MasterService;
+
 import java.util.List;
 
 public interface ClusterStateTaskListener {
@@ -28,7 +30,8 @@ public interface ClusterStateTaskListener {
     void onFailure(String source, Exception e);
 
     /**
-     * called when the task was rejected because the local node is no longer master
+     * called when the task was rejected because the local node is no longer master.
+     * Used only for tasks submitted to {@link MasterService}.
      */
     default void onNoLongerMaster(String source) {
         onFailure(source, new NotMasterException("no longer master. source: [" + source + "]"));

core/src/main/java/org/elasticsearch/cluster/LocalClusterUpdateTask.java

@@ -50,25 +50,11 @@ public abstract class LocalClusterUpdateTask implements ClusterStateTaskConfig,
         return ClusterTasksResult.<LocalClusterUpdateTask>builder().successes(tasks).build(result, currentState);
     }
 
-    /**
-     * node stepped down as master or has lost connection to the master
-     */
-    public static ClusterTasksResult<LocalClusterUpdateTask> noMaster() {
-        return new ClusterTasksResult(true, null, null);
-    }
-
     /**
      * no changes were made to the cluster state. Useful to execute a runnable on the cluster state applier thread
      */
     public static ClusterTasksResult<LocalClusterUpdateTask> unchanged() {
-        return new ClusterTasksResult(false, null, null);
+        return new ClusterTasksResult<>(null, null);
-    }
-
-    /**
-     * locally apply cluster state received from a master
-     */
-    public static ClusterTasksResult<LocalClusterUpdateTask> newState(ClusterState clusterState) {
-        return new ClusterTasksResult(false, clusterState, null);
     }
 
     @Override

core/src/main/java/org/elasticsearch/cluster/routing/DelayedAllocationService.java

@@ -178,8 +178,8 @@ public class DelayedAllocationService extends AbstractLifecycleComponent impleme
     /**
      * Figure out if an existing scheduled reroute is good enough or whether we need to cancel and reschedule.
      */
-    private void scheduleIfNeeded(long currentNanoTime, ClusterState state) {
+    private synchronized void scheduleIfNeeded(long currentNanoTime, ClusterState state) {
-        assertClusterStateThread();
+        assertClusterOrMasterStateThread();
         long nextDelayNanos = UnassignedInfo.findNextDelayedAllocation(currentNanoTime, state);
         if (nextDelayNanos < 0) {
             logger.trace("no need to schedule reroute - no delayed unassigned shards");
@@ -214,7 +214,7 @@ public class DelayedAllocationService extends AbstractLifecycleComponent impleme
     }
 
     // protected so that it can be overridden (and disabled) by unit tests
-    protected void assertClusterStateThread() {
+    protected void assertClusterOrMasterStateThread() {
-        ClusterService.assertClusterStateThread();
+        assert ClusterService.assertClusterOrMasterStateThread();
     }
 }

core/src/main/java/org/elasticsearch/cluster/service/ClusterApplier.java

@@ -0,0 +1,37 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.cluster.service;
+
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
+
+import java.util.function.Supplier;
+
+@FunctionalInterface
+public interface ClusterApplier {
+    /**
+     * Method to invoke when a new cluster state is available to be applied
+     *
+     * @param source information where the cluster state came from
+     * @param clusterStateSupplier the cluster state supplier which provides the latest cluster state to apply
+     * @param listener callback that is invoked after cluster state is applied
+     */
+    void onNewClusterState(String source, Supplier<ClusterState> clusterStateSupplier, ClusterStateTaskListener listener);
+}

core/src/main/java/org/elasticsearch/cluster/service/ClusterApplierService.java

@@ -0,0 +1,655 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.cluster.service;
+
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.apache.logging.log4j.util.Supplier;
+import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateApplier;
+import org.elasticsearch.cluster.ClusterStateListener;
+import org.elasticsearch.cluster.ClusterStateObserver;
+import org.elasticsearch.cluster.ClusterStateTaskConfig;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
+import org.elasticsearch.cluster.LocalNodeMasterListener;
+import org.elasticsearch.cluster.NodeConnectionsService;
+import org.elasticsearch.cluster.TimeoutClusterStateListener;
+import org.elasticsearch.cluster.metadata.ProcessClusterEventTimeoutException;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.Priority;
+import org.elasticsearch.common.component.AbstractLifecycleComponent;
+import org.elasticsearch.common.settings.ClusterSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
+import org.elasticsearch.common.util.concurrent.EsExecutors;
+import org.elasticsearch.common.util.concurrent.EsRejectedExecutionException;
+import org.elasticsearch.common.util.concurrent.FutureUtils;
+import org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor;
+import org.elasticsearch.common.util.iterable.Iterables;
+import org.elasticsearch.threadpool.ThreadPool;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+import java.util.Queue;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import static org.elasticsearch.cluster.service.ClusterService.CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING;
+import static org.elasticsearch.common.util.concurrent.EsExecutors.daemonThreadFactory;
+
+public class ClusterApplierService extends AbstractLifecycleComponent implements ClusterApplier {
+
+    public static final String CLUSTER_UPDATE_THREAD_NAME = "clusterApplierService#updateTask";
+
+    private final ClusterSettings clusterSettings;
+    protected final ThreadPool threadPool;
+
+    private volatile TimeValue slowTaskLoggingThreshold;
+
+    private volatile PrioritizedEsThreadPoolExecutor threadPoolExecutor;
+
+    /**
+     * Those 3 state listeners are changing infrequently - CopyOnWriteArrayList is just fine
+     */
+    private final Collection<ClusterStateApplier> highPriorityStateAppliers = new CopyOnWriteArrayList<>();
+    private final Collection<ClusterStateApplier> normalPriorityStateAppliers = new CopyOnWriteArrayList<>();
+    private final Collection<ClusterStateApplier> lowPriorityStateAppliers = new CopyOnWriteArrayList<>();
+    private final Iterable<ClusterStateApplier> clusterStateAppliers = Iterables.concat(highPriorityStateAppliers,
+        normalPriorityStateAppliers, lowPriorityStateAppliers);
+
+    private final Collection<ClusterStateListener> clusterStateListeners = new CopyOnWriteArrayList<>();
+    private final Collection<TimeoutClusterStateListener> timeoutClusterStateListeners =
+        Collections.newSetFromMap(new ConcurrentHashMap<TimeoutClusterStateListener, Boolean>());
+
+    private final LocalNodeMasterListeners localNodeMasterListeners;
+
+    private final Queue<NotifyTimeout> onGoingTimeouts = ConcurrentCollections.newQueue();
+
+    private final AtomicReference<ClusterState> state; // last applied state
+
+    private NodeConnectionsService nodeConnectionsService;
+
+    public ClusterApplierService(Settings settings, ClusterSettings clusterSettings, ThreadPool threadPool) {
+        super(settings);
+        this.clusterSettings = clusterSettings;
+        this.threadPool = threadPool;
+        this.state = new AtomicReference<>();
+        this.slowTaskLoggingThreshold = CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING.get(settings);
+        this.localNodeMasterListeners = new LocalNodeMasterListeners(threadPool);
+    }
+
+    public void setSlowTaskLoggingThreshold(TimeValue slowTaskLoggingThreshold) {
+        this.slowTaskLoggingThreshold = slowTaskLoggingThreshold;
+    }
+
+    public synchronized void setNodeConnectionsService(NodeConnectionsService nodeConnectionsService) {
+        assert this.nodeConnectionsService == null : "nodeConnectionsService is already set";
+        this.nodeConnectionsService = nodeConnectionsService;
+    }
+
+    public void setInitialState(ClusterState initialState) {
+        if (lifecycle.started()) {
+            throw new IllegalStateException("can't set initial state when started");
+        }
+        assert state.get() == null : "state is already set";
+        state.set(initialState);
+    }
+
+    @Override
+    protected synchronized void doStart() {
+        Objects.requireNonNull(nodeConnectionsService, "please set the node connection service before starting");
+        Objects.requireNonNull(state.get(), "please set initial state before starting");
+        addListener(localNodeMasterListeners);
+        threadPoolExecutor = EsExecutors.newSinglePrioritizing(CLUSTER_UPDATE_THREAD_NAME,
+            daemonThreadFactory(settings, CLUSTER_UPDATE_THREAD_NAME), threadPool.getThreadContext(), threadPool.scheduler());
+    }
+
+    class UpdateTask extends SourcePrioritizedRunnable implements Function<ClusterState, ClusterState> {
+        final ClusterStateTaskListener listener;
+        final Function<ClusterState, ClusterState> updateFunction;
+
+        UpdateTask(Priority priority, String source, ClusterStateTaskListener listener,
+                   Function<ClusterState, ClusterState> updateFunction) {
+            super(priority, source);
+            this.listener = listener;
+            this.updateFunction = updateFunction;
+        }
+
+        @Override
+        public ClusterState apply(ClusterState clusterState) {
+            return updateFunction.apply(clusterState);
+        }
+
+        @Override
+        public void run() {
+            runTask(this);
+        }
+    }
+
+    @Override
+    protected synchronized void doStop() {
+        for (NotifyTimeout onGoingTimeout : onGoingTimeouts) {
+            onGoingTimeout.cancel();
+            try {
+                onGoingTimeout.cancel();
+                onGoingTimeout.listener.onClose();
+            } catch (Exception ex) {
+                logger.debug("failed to notify listeners on shutdown", ex);
+            }
+        }
+        ThreadPool.terminate(threadPoolExecutor, 10, TimeUnit.SECONDS);
+        // close timeout listeners that did not have an ongoing timeout
+        timeoutClusterStateListeners.forEach(TimeoutClusterStateListener::onClose);
+        removeListener(localNodeMasterListeners);
+    }
+
+    @Override
+    protected synchronized void doClose() {
+    }
+
+    /**
+     * The current cluster state.
+     * Should be renamed to appliedClusterState
+     */
+    public ClusterState state() {
+        assert assertNotCalledFromClusterStateApplier("the applied cluster state is not yet available");
+        ClusterState clusterState = this.state.get();
+        assert clusterState != null : "initial cluster state not set yet";
+        return clusterState;
+    }
+
+    /**
+     * Adds a high priority applier of updated cluster states.
+     */
+    public void addHighPriorityApplier(ClusterStateApplier applier) {
+        highPriorityStateAppliers.add(applier);
+    }
+
+    /**
+     * Adds an applier which will be called after all high priority and normal appliers have been called.
+     */
+    public void addLowPriorityApplier(ClusterStateApplier applier) {
+        lowPriorityStateAppliers.add(applier);
+    }
+
+    /**
+     * Adds a applier of updated cluster states.
+     */
+    public void addStateApplier(ClusterStateApplier applier) {
+        normalPriorityStateAppliers.add(applier);
+    }
+
+    /**
+     * Removes an applier of updated cluster states.
+     */
+    public void removeApplier(ClusterStateApplier applier) {
+        normalPriorityStateAppliers.remove(applier);
+        highPriorityStateAppliers.remove(applier);
+        lowPriorityStateAppliers.remove(applier);
+    }
+
+    /**
+     * Add a listener for updated cluster states
+     */
+    public void addListener(ClusterStateListener listener) {
+        clusterStateListeners.add(listener);
+    }
+
+    /**
+     * Removes a listener for updated cluster states.
+     */
+    public void removeListener(ClusterStateListener listener) {
+        clusterStateListeners.remove(listener);
+    }
+
+    /**
+     * Removes a timeout listener for updated cluster states.
+     */
+    public void removeTimeoutListener(TimeoutClusterStateListener listener) {
+        timeoutClusterStateListeners.remove(listener);
+        for (Iterator<NotifyTimeout> it = onGoingTimeouts.iterator(); it.hasNext(); ) {
+            NotifyTimeout timeout = it.next();
+            if (timeout.listener.equals(listener)) {
+                timeout.cancel();
+                it.remove();
+            }
+        }
+    }
+
+    /**
+     * Add a listener for on/off local node master events
+     */
+    public void addLocalNodeMasterListener(LocalNodeMasterListener listener) {
+        localNodeMasterListeners.add(listener);
+    }
+
+    /**
+     * Remove the given listener for on/off local master events
+     */
+    public void removeLocalNodeMasterListener(LocalNodeMasterListener listener) {
+        localNodeMasterListeners.remove(listener);
+    }
+
+    /**
+     * Adds a cluster state listener that is expected to be removed during a short period of time.
+     * If provided, the listener will be notified once a specific time has elapsed.
+     *
+     * NOTE: the listener is not removed on timeout. This is the responsibility of the caller.
+     */
+    public void addTimeoutListener(@Nullable final TimeValue timeout, final TimeoutClusterStateListener listener) {
+        if (lifecycle.stoppedOrClosed()) {
+            listener.onClose();
+            return;
+        }
+        // call the post added notification on the same event thread
+        try {
+            threadPoolExecutor.execute(new SourcePrioritizedRunnable(Priority.HIGH, "_add_listener_") {
+                @Override
+                public void run() {
+                    if (timeout != null) {
+                        NotifyTimeout notifyTimeout = new NotifyTimeout(listener, timeout);
+                        notifyTimeout.future = threadPool.schedule(timeout, ThreadPool.Names.GENERIC, notifyTimeout);
+                        onGoingTimeouts.add(notifyTimeout);
+                    }
+                    timeoutClusterStateListeners.add(listener);
+                    listener.postAdded();
+                }
+            });
+        } catch (EsRejectedExecutionException e) {
+            if (lifecycle.stoppedOrClosed()) {
+                listener.onClose();
+            } else {
+                throw e;
+            }
+        }
+    }
+
+    public void runOnApplierThread(final String source, Consumer<ClusterState> clusterStateConsumer,
+                                   final ClusterStateTaskListener listener, Priority priority) {
+        submitStateUpdateTask(source, ClusterStateTaskConfig.build(priority),
+            (clusterState) -> {
+                clusterStateConsumer.accept(clusterState);
+                return clusterState;
+            },
+            listener);
+    }
+
+    public void runOnApplierThread(final String source, Consumer<ClusterState> clusterStateConsumer,
+                                   final ClusterStateTaskListener listener) {
+        runOnApplierThread(source, clusterStateConsumer, listener, Priority.HIGH);
+    }
+
+    @Override
+    public void onNewClusterState(final String source, final java.util.function.Supplier<ClusterState> clusterStateSupplier,
+                                  final ClusterStateTaskListener listener) {
+        Function<ClusterState, ClusterState> applyFunction = currentState -> {
+            ClusterState nextState = clusterStateSupplier.get();
+            if (nextState != null) {
+                return nextState;
+            } else {
+                return currentState;
+            }
+        };
+        submitStateUpdateTask(source, ClusterStateTaskConfig.build(Priority.HIGH), applyFunction, listener);
+    }
+
+    private void submitStateUpdateTask(final String source, final ClusterStateTaskConfig config,
+                                       final Function<ClusterState, ClusterState> executor,
+                                       final ClusterStateTaskListener listener) {
+        if (!lifecycle.started()) {
+            return;
+        }
+        try {
+            UpdateTask updateTask = new UpdateTask(config.priority(), source, new SafeClusterStateTaskListener(listener, logger), executor);
+            if (config.timeout() != null) {
+                threadPoolExecutor.execute(updateTask, config.timeout(),
+                    () -> threadPool.generic().execute(
+                        () -> listener.onFailure(source, new ProcessClusterEventTimeoutException(config.timeout(), source))));
+            } else {
+                threadPoolExecutor.execute(updateTask);
+            }
+        } catch (EsRejectedExecutionException e) {
+            // ignore cases where we are shutting down..., there is really nothing interesting
+            // to be done here...
+            if (!lifecycle.stoppedOrClosed()) {
+                throw e;
+            }
+        }
+    }
+
+    /** asserts that the current thread is the cluster state update thread */
+    public static boolean assertClusterStateUpdateThread() {
+        assert Thread.currentThread().getName().contains(ClusterApplierService.CLUSTER_UPDATE_THREAD_NAME) :
+            "not called from the cluster state update thread";
+        return true;
+    }
+
+    /** asserts that the current thread is <b>NOT</b> the cluster state update thread */
+    public static boolean assertNotClusterStateUpdateThread(String reason) {
+        assert Thread.currentThread().getName().contains(CLUSTER_UPDATE_THREAD_NAME) == false :
+            "Expected current thread [" + Thread.currentThread() + "] to not be the cluster state update thread. Reason: [" + reason + "]";
+        return true;
+    }
+
+    /** asserts that the current stack trace does <b>NOT</b> involve a cluster state applier */
+    private static boolean assertNotCalledFromClusterStateApplier(String reason) {
+        if (Thread.currentThread().getName().contains(CLUSTER_UPDATE_THREAD_NAME)) {
+            for (StackTraceElement element : Thread.currentThread().getStackTrace()) {
+                final String className = element.getClassName();
+                final String methodName = element.getMethodName();
+                if (className.equals(ClusterStateObserver.class.getName())) {
+                    // people may start an observer from an applier
+                    return true;
+                } else if (className.equals(ClusterApplierService.class.getName())
+                    && methodName.equals("callClusterStateAppliers")) {
+                    throw new AssertionError("should not be called by a cluster state applier. reason [" + reason + "]");
+                }
+            }
+        }
+        return true;
+    }
+
+    protected void runTask(UpdateTask task) {
+        if (!lifecycle.started()) {
+            logger.debug("processing [{}]: ignoring, cluster applier service not started", task.source);
+            return;
+        }
+
+        logger.debug("processing [{}]: execute", task.source);
+        final ClusterState previousClusterState = state.get();
+
+        long startTimeNS = currentTimeInNanos();
+        final ClusterState newClusterState;
+        try {
+            newClusterState = task.apply(previousClusterState);
+        } catch (Exception e) {
+            TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+            if (logger.isTraceEnabled()) {
+                logger.trace(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "failed to execute cluster state applier in [{}], state:\nversion [{}], source [{}]\n{}{}{}",
+                        executionTime,
+                        previousClusterState.version(),
+                        task.source,
+                        previousClusterState.nodes(),
+                        previousClusterState.routingTable(),
+                        previousClusterState.getRoutingNodes()),
+                    e);
+            }
+            warnAboutSlowTaskIfNeeded(executionTime, task.source);
+            task.listener.onFailure(task.source, e);
+            return;
+        }
+
+        if (previousClusterState == newClusterState) {
+            task.listener.clusterStateProcessed(task.source, newClusterState, newClusterState);
+            TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+            logger.debug("processing [{}]: took [{}] no change in cluster state", task.source, executionTime);
+            warnAboutSlowTaskIfNeeded(executionTime, task.source);
+        } else {
+            if (logger.isTraceEnabled()) {
+                logger.trace("cluster state updated, source [{}]\n{}", task.source, newClusterState);
+            } else if (logger.isDebugEnabled()) {
+                logger.debug("cluster state updated, version [{}], source [{}]", newClusterState.version(), task.source);
+            }
+            try {
+                applyChanges(task, previousClusterState, newClusterState);
+                TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+                logger.debug("processing [{}]: took [{}] done applying updated cluster state (version: {}, uuid: {})", task.source,
+                    executionTime, newClusterState.version(),
+                    newClusterState.stateUUID());
+                warnAboutSlowTaskIfNeeded(executionTime, task.source);
+            } catch (Exception e) {
+                TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+                final long version = newClusterState.version();
+                final String stateUUID = newClusterState.stateUUID();
+                final String fullState = newClusterState.toString();
+                logger.warn(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "failed to apply updated cluster state in [{}]:\nversion [{}], uuid [{}], source [{}]\n{}",
+                        executionTime,
+                        version,
+                        stateUUID,
+                        task.source,
+                        fullState),
+                    e);
+                // TODO: do we want to call updateTask.onFailure here?
+            }
+        }
+    }
+
+    private void applyChanges(UpdateTask task, ClusterState previousClusterState, ClusterState newClusterState) {
+        ClusterChangedEvent clusterChangedEvent = new ClusterChangedEvent(task.source, newClusterState, previousClusterState);
+        // new cluster state, notify all listeners
+        final DiscoveryNodes.Delta nodesDelta = clusterChangedEvent.nodesDelta();
+        if (nodesDelta.hasChanges() && logger.isInfoEnabled()) {
+            String summary = nodesDelta.shortSummary();
+            if (summary.length() > 0) {
+                logger.info("{}, reason: {}", summary, task.source);
+            }
+        }
+
+        nodeConnectionsService.connectToNodes(newClusterState.nodes());
+
+        logger.debug("applying cluster state version {}", newClusterState.version());
+        try {
+            // nothing to do until we actually recover from the gateway or any other block indicates we need to disable persistency
+            if (clusterChangedEvent.state().blocks().disableStatePersistence() == false && clusterChangedEvent.metaDataChanged()) {
+                final Settings incomingSettings = clusterChangedEvent.state().metaData().settings();
+                clusterSettings.applySettings(incomingSettings);
+            }
+        } catch (Exception ex) {
+            logger.warn("failed to apply cluster settings", ex);
+        }
+
+        logger.debug("apply cluster state with version {}", newClusterState.version());
+        callClusterStateAppliers(clusterChangedEvent);
+
+        nodeConnectionsService.disconnectFromNodesExcept(newClusterState.nodes());
+
+        logger.debug("set locally applied cluster state to version {}", newClusterState.version());
+        state.set(newClusterState);
+
+        callClusterStateListeners(clusterChangedEvent);
+
+        task.listener.clusterStateProcessed(task.source, previousClusterState, newClusterState);
+    }
+
+    private void callClusterStateAppliers(ClusterChangedEvent clusterChangedEvent) {
+        clusterStateAppliers.forEach(applier -> {
+            try {
+                logger.trace("calling [{}] with change to version [{}]", applier, clusterChangedEvent.state().version());
+                applier.applyClusterState(clusterChangedEvent);
+            } catch (Exception ex) {
+                logger.warn("failed to notify ClusterStateApplier", ex);
+            }
+        });
+    }
+
+    private void callClusterStateListeners(ClusterChangedEvent clusterChangedEvent) {
+        Stream.concat(clusterStateListeners.stream(), timeoutClusterStateListeners.stream()).forEach(listener -> {
+            try {
+                logger.trace("calling [{}] with change to version [{}]", listener, clusterChangedEvent.state().version());
+                listener.clusterChanged(clusterChangedEvent);
+            } catch (Exception ex) {
+                logger.warn("failed to notify ClusterStateListener", ex);
+            }
+        });
+    }
+
+    private static class SafeClusterStateTaskListener implements ClusterStateTaskListener {
+        private final ClusterStateTaskListener listener;
+        private final Logger logger;
+
+        SafeClusterStateTaskListener(ClusterStateTaskListener listener, Logger logger) {
+            this.listener = listener;
+            this.logger = logger;
+        }
+
+        @Override
+        public void onFailure(String source, Exception e) {
+            try {
+                listener.onFailure(source, e);
+            } catch (Exception inner) {
+                inner.addSuppressed(e);
+                logger.error(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "exception thrown by listener notifying of failure from [{}]", source), inner);
+            }
+        }
+
+        @Override
+        public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+            try {
+                listener.clusterStateProcessed(source, oldState, newState);
+            } catch (Exception e) {
+                logger.error(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "exception thrown by listener while notifying of cluster state processed from [{}], old cluster state:\n" +
+                            "{}\nnew cluster state:\n{}",
+                        source, oldState, newState),
+                    e);
+            }
+        }
+    }
+
+    protected void warnAboutSlowTaskIfNeeded(TimeValue executionTime, String source) {
+        if (executionTime.getMillis() > slowTaskLoggingThreshold.getMillis()) {
+            logger.warn("cluster state applier task [{}] took [{}] above the warn threshold of {}", source, executionTime,
+                slowTaskLoggingThreshold);
+        }
+    }
+
+    class NotifyTimeout implements Runnable {
+        final TimeoutClusterStateListener listener;
+        final TimeValue timeout;
+        volatile ScheduledFuture future;
+
+        NotifyTimeout(TimeoutClusterStateListener listener, TimeValue timeout) {
+            this.listener = listener;
+            this.timeout = timeout;
+        }
+
+        public void cancel() {
+            FutureUtils.cancel(future);
+        }
+
+        @Override
+        public void run() {
+            if (future != null && future.isCancelled()) {
+                return;
+            }
+            if (lifecycle.stoppedOrClosed()) {
+                listener.onClose();
+            } else {
+                listener.onTimeout(this.timeout);
+            }
+            // note, we rely on the listener to remove itself in case of timeout if needed
+        }
+    }
+
+    private static class LocalNodeMasterListeners implements ClusterStateListener {
+
+        private final List<LocalNodeMasterListener> listeners = new CopyOnWriteArrayList<>();
+        private final ThreadPool threadPool;
+        private volatile boolean master = false;
+
+        private LocalNodeMasterListeners(ThreadPool threadPool) {
+            this.threadPool = threadPool;
+        }
+
+        @Override
+        public void clusterChanged(ClusterChangedEvent event) {
+            if (!master && event.localNodeMaster()) {
+                master = true;
+                for (LocalNodeMasterListener listener : listeners) {
+                    java.util.concurrent.Executor executor = threadPool.executor(listener.executorName());
+                    executor.execute(new OnMasterRunnable(listener));
+                }
+                return;
+            }
+
+            if (master && !event.localNodeMaster()) {
+                master = false;
+                for (LocalNodeMasterListener listener : listeners) {
+                    java.util.concurrent.Executor executor = threadPool.executor(listener.executorName());
+                    executor.execute(new OffMasterRunnable(listener));
+                }
+            }
+        }
+
+        private void add(LocalNodeMasterListener listener) {
+            listeners.add(listener);
+        }
+
+        private void remove(LocalNodeMasterListener listener) {
+            listeners.remove(listener);
+        }
+
+        private void clear() {
+            listeners.clear();
+        }
+    }
+
+    private static class OnMasterRunnable implements Runnable {
+
+        private final LocalNodeMasterListener listener;
+
+        private OnMasterRunnable(LocalNodeMasterListener listener) {
+            this.listener = listener;
+        }
+
+        @Override
+        public void run() {
+            listener.onMaster();
+        }
+    }
+
+    private static class OffMasterRunnable implements Runnable {
+
+        private final LocalNodeMasterListener listener;
+
+        private OffMasterRunnable(LocalNodeMasterListener listener) {
+            this.listener = listener;
+        }
+
+        @Override
+        public void run() {
+            listener.offMaster();
+        }
+    }
+
+    // this one is overridden in tests so we can control time
+    protected long currentTimeInNanos() {
+        return System.nanoTime();
+    }
+}

core/src/main/java/org/elasticsearch/cluster/service/MasterService.java

@@ -0,0 +1,752 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.cluster.service;
+
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.apache.logging.log4j.util.Supplier;
+import org.elasticsearch.cluster.AckedClusterStateTaskListener;
+import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterState.Builder;
+import org.elasticsearch.cluster.ClusterStateTaskConfig;
+import org.elasticsearch.cluster.ClusterStateTaskExecutor;
+import org.elasticsearch.cluster.ClusterStateTaskExecutor.ClusterTasksResult;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
+import org.elasticsearch.cluster.metadata.MetaData;
+import org.elasticsearch.cluster.metadata.ProcessClusterEventTimeoutException;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.routing.RoutingTable;
+import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.Priority;
+import org.elasticsearch.common.component.AbstractLifecycleComponent;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.text.Text;
+import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.common.util.concurrent.CountDown;
+import org.elasticsearch.common.util.concurrent.EsExecutors;
+import org.elasticsearch.common.util.concurrent.EsRejectedExecutionException;
+import org.elasticsearch.common.util.concurrent.FutureUtils;
+import org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor;
+import org.elasticsearch.discovery.Discovery;
+import org.elasticsearch.threadpool.ThreadPool;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.function.BiConsumer;
+import java.util.stream.Collectors;
+
+import static org.elasticsearch.cluster.service.ClusterService.CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING;
+import static org.elasticsearch.common.util.concurrent.EsExecutors.daemonThreadFactory;
+
+public class MasterService extends AbstractLifecycleComponent {
+
+    public static final String MASTER_UPDATE_THREAD_NAME = "masterService#updateTask";
+
+    private BiConsumer<ClusterChangedEvent, Discovery.AckListener> clusterStatePublisher;
+
+    private java.util.function.Supplier<ClusterState> clusterStateSupplier;
+
+    private volatile TimeValue slowTaskLoggingThreshold;
+
+    protected final ThreadPool threadPool;
+
+    private volatile PrioritizedEsThreadPoolExecutor threadPoolExecutor;
+    private volatile Batcher taskBatcher;
+
+    public MasterService(Settings settings, ThreadPool threadPool) {
+        super(settings);
+        // TODO: introduce a dedicated setting for master service
+        this.slowTaskLoggingThreshold = CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING.get(settings);
+        this.threadPool = threadPool;
+    }
+
+    public void setSlowTaskLoggingThreshold(TimeValue slowTaskLoggingThreshold) {
+        this.slowTaskLoggingThreshold = slowTaskLoggingThreshold;
+    }
+
+    public synchronized void setClusterStatePublisher(BiConsumer<ClusterChangedEvent, Discovery.AckListener> publisher) {
+        clusterStatePublisher = publisher;
+    }
+
+    public synchronized void setClusterStateSupplier(java.util.function.Supplier<ClusterState> clusterStateSupplier) {
+        this.clusterStateSupplier = clusterStateSupplier;
+    }
+
+    @Override
+    protected synchronized void doStart() {
+        Objects.requireNonNull(clusterStatePublisher, "please set a cluster state publisher before starting");
+        Objects.requireNonNull(clusterStateSupplier, "please set a cluster state supplier before starting");
+        threadPoolExecutor = EsExecutors.newSinglePrioritizing(MASTER_UPDATE_THREAD_NAME,
+            daemonThreadFactory(settings, MASTER_UPDATE_THREAD_NAME), threadPool.getThreadContext(), threadPool.scheduler());
+        taskBatcher = new Batcher(logger, threadPoolExecutor);
+    }
+
+    class Batcher extends TaskBatcher {
+
+        Batcher(Logger logger, PrioritizedEsThreadPoolExecutor threadExecutor) {
+            super(logger, threadExecutor);
+        }
+
+        @Override
+        protected void onTimeout(List<? extends BatchedTask> tasks, TimeValue timeout) {
+            threadPool.generic().execute(
+                () -> tasks.forEach(
+                    task -> ((UpdateTask) task).listener.onFailure(task.source,
+                        new ProcessClusterEventTimeoutException(timeout, task.source))));
+        }
+
+        @Override
+        protected void run(Object batchingKey, List<? extends BatchedTask> tasks, String tasksSummary) {
+            ClusterStateTaskExecutor<Object> taskExecutor = (ClusterStateTaskExecutor<Object>) batchingKey;
+            List<UpdateTask> updateTasks = (List<UpdateTask>) tasks;
+            runTasks(new TaskInputs(taskExecutor, updateTasks, tasksSummary));
+        }
+
+        class UpdateTask extends BatchedTask {
+            final ClusterStateTaskListener listener;
+
+            UpdateTask(Priority priority, String source, Object task, ClusterStateTaskListener listener,
+                       ClusterStateTaskExecutor<?> executor) {
+                super(priority, source, executor, task);
+                this.listener = listener;
+            }
+
+            @Override
+            public String describeTasks(List<? extends BatchedTask> tasks) {
+                return ((ClusterStateTaskExecutor<Object>) batchingKey).describeTasks(
+                    tasks.stream().map(BatchedTask::getTask).collect(Collectors.toList()));
+            }
+        }
+    }
+
+    @Override
+    protected synchronized void doStop() {
+        ThreadPool.terminate(threadPoolExecutor, 10, TimeUnit.SECONDS);
+    }
+
+    @Override
+    protected synchronized void doClose() {
+    }
+
+    /**
+     * The current cluster state exposed by the discovery layer. Package-visible for tests.
+     */
+    ClusterState state() {
+        return clusterStateSupplier.get();
+    }
+
+    public static boolean assertMasterUpdateThread() {
+        assert Thread.currentThread().getName().contains(MASTER_UPDATE_THREAD_NAME) :
+            "not called from the master service thread";
+        return true;
+    }
+
+    public static boolean assertNotMasterUpdateThread(String reason) {
+        assert Thread.currentThread().getName().contains(MASTER_UPDATE_THREAD_NAME) == false :
+            "Expected current thread [" + Thread.currentThread() + "] to not be the master service thread. Reason: [" + reason + "]";
+        return true;
+    }
+
+    protected void runTasks(TaskInputs taskInputs) {
+        final String summary = taskInputs.summary;
+        if (!lifecycle.started()) {
+            logger.debug("processing [{}]: ignoring, master service not started", summary);
+            return;
+        }
+
+        logger.debug("processing [{}]: execute", summary);
+        final ClusterState previousClusterState = state();
+
+        if (!previousClusterState.nodes().isLocalNodeElectedMaster() && taskInputs.runOnlyWhenMaster()) {
+            logger.debug("failing [{}]: local node is no longer master", summary);
+            taskInputs.onNoLongerMaster();
+            return;
+        }
+
+        long startTimeNS = currentTimeInNanos();
+        TaskOutputs taskOutputs = calculateTaskOutputs(taskInputs, previousClusterState, startTimeNS);
+        taskOutputs.notifyFailedTasks();
+
+        if (taskOutputs.clusterStateUnchanged()) {
+            taskOutputs.notifySuccessfulTasksOnUnchangedClusterState();
+            TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+            logger.debug("processing [{}]: took [{}] no change in cluster state", summary, executionTime);
+            warnAboutSlowTaskIfNeeded(executionTime, summary);
+        } else {
+            ClusterState newClusterState = taskOutputs.newClusterState;
+            if (logger.isTraceEnabled()) {
+                logger.trace("cluster state updated, source [{}]\n{}", summary, newClusterState);
+            } else if (logger.isDebugEnabled()) {
+                logger.debug("cluster state updated, version [{}], source [{}]", newClusterState.version(), summary);
+            }
+            try {
+                ClusterChangedEvent clusterChangedEvent = new ClusterChangedEvent(summary, newClusterState, previousClusterState);
+                // new cluster state, notify all listeners
+                final DiscoveryNodes.Delta nodesDelta = clusterChangedEvent.nodesDelta();
+                if (nodesDelta.hasChanges() && logger.isInfoEnabled()) {
+                    String nodeSummary = nodesDelta.shortSummary();
+                    if (nodeSummary.length() > 0) {
+                        logger.info("{}, reason: {}", summary, nodeSummary);
+                    }
+                }
+
+                logger.debug("publishing cluster state version [{}]", newClusterState.version());
+                try {
+                    clusterStatePublisher.accept(clusterChangedEvent, taskOutputs.createAckListener(threadPool, newClusterState));
+                } catch (Discovery.FailedToCommitClusterStateException t) {
+                    final long version = newClusterState.version();
+                    logger.warn(
+                        (Supplier<?>) () -> new ParameterizedMessage(
+                            "failing [{}]: failed to commit cluster state version [{}]", summary, version),
+                        t);
+                    taskOutputs.publishingFailed(t);
+                    return;
+                }
+
+                taskOutputs.processedDifferentClusterState(previousClusterState, newClusterState);
+
+                try {
+                    taskOutputs.clusterStatePublished(clusterChangedEvent);
+                } catch (Exception e) {
+                    logger.error(
+                        (Supplier<?>) () -> new ParameterizedMessage(
+                            "exception thrown while notifying executor of new cluster state publication [{}]",
+                            summary),
+                        e);
+                }
+                TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+                logger.debug("processing [{}]: took [{}] done publishing updated cluster state (version: {}, uuid: {})", summary,
+                    executionTime, newClusterState.version(),
+                    newClusterState.stateUUID());
+                warnAboutSlowTaskIfNeeded(executionTime, summary);
+            } catch (Exception e) {
+                TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+                final long version = newClusterState.version();
+                final String stateUUID = newClusterState.stateUUID();
+                final String fullState = newClusterState.toString();
+                logger.warn(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "failed to publish updated cluster state in [{}]:\nversion [{}], uuid [{}], source [{}]\n{}",
+                        executionTime,
+                        version,
+                        stateUUID,
+                        summary,
+                        fullState),
+                    e);
+                // TODO: do we want to call updateTask.onFailure here?
+            }
+        }
+    }
+
+    public TaskOutputs calculateTaskOutputs(TaskInputs taskInputs, ClusterState previousClusterState, long startTimeNS) {
+        ClusterTasksResult<Object> clusterTasksResult = executeTasks(taskInputs, startTimeNS, previousClusterState);
+        ClusterState newClusterState = patchVersions(previousClusterState, clusterTasksResult);
+        return new TaskOutputs(taskInputs, previousClusterState, newClusterState, getNonFailedTasks(taskInputs, clusterTasksResult),
+            clusterTasksResult.executionResults);
+    }
+
+    private ClusterState patchVersions(ClusterState previousClusterState, ClusterTasksResult<?> executionResult) {
+        ClusterState newClusterState = executionResult.resultingState;
+
+        if (previousClusterState != newClusterState) {
+            // only the master controls the version numbers
+            Builder builder = ClusterState.builder(newClusterState).incrementVersion();
+            if (previousClusterState.routingTable() != newClusterState.routingTable()) {
+                builder.routingTable(RoutingTable.builder(newClusterState.routingTable())
+                    .version(newClusterState.routingTable().version() + 1).build());
+            }
+            if (previousClusterState.metaData() != newClusterState.metaData()) {
+                builder.metaData(MetaData.builder(newClusterState.metaData()).version(newClusterState.metaData().version() + 1));
+            }
+
+            newClusterState = builder.build();
+        }
+
+        return newClusterState;
+    }
+
+    /**
+     * Submits a cluster state update task; unlike {@link #submitStateUpdateTask(String, Object, ClusterStateTaskConfig,
+     * ClusterStateTaskExecutor, ClusterStateTaskListener)}, submitted updates will not be batched.
+     *
+     * @param source     the source of the cluster state update task
+     * @param updateTask the full context for the cluster state update
+     *                   task
+     *
+     */
+    public <T extends ClusterStateTaskConfig & ClusterStateTaskExecutor<T> & ClusterStateTaskListener>
+        void submitStateUpdateTask(
+        String source, T updateTask) {
+        submitStateUpdateTask(source, updateTask, updateTask, updateTask, updateTask);
+    }
+
+    /**
+     * Submits a cluster state update task; submitted updates will be
+     * batched across the same instance of executor. The exact batching
+     * semantics depend on the underlying implementation but a rough
+     * guideline is that if the update task is submitted while there
+     * are pending update tasks for the same executor, these update
+     * tasks will all be executed on the executor in a single batch
+     *
+     * @param source   the source of the cluster state update task
+     * @param task     the state needed for the cluster state update task
+     * @param config   the cluster state update task configuration
+     * @param executor the cluster state update task executor; tasks
+     *                 that share the same executor will be executed
+     *                 batches on this executor
+     * @param listener callback after the cluster state update task
+     *                 completes
+     * @param <T>      the type of the cluster state update task state
+     *
+     */
+    public <T> void submitStateUpdateTask(String source, T task,
+                                          ClusterStateTaskConfig config,
+                                          ClusterStateTaskExecutor<T> executor,
+                                          ClusterStateTaskListener listener) {
+        submitStateUpdateTasks(source, Collections.singletonMap(task, listener), config, executor);
+    }
+
+    /**
+     * Output created by executing a set of tasks provided as TaskInputs
+     */
+    class TaskOutputs {
+        public final TaskInputs taskInputs;
+        public final ClusterState previousClusterState;
+        public final ClusterState newClusterState;
+        public final List<Batcher.UpdateTask> nonFailedTasks;
+        public final Map<Object, ClusterStateTaskExecutor.TaskResult> executionResults;
+
+        TaskOutputs(TaskInputs taskInputs, ClusterState previousClusterState,
+                           ClusterState newClusterState,
+                           List<Batcher.UpdateTask> nonFailedTasks,
+                           Map<Object, ClusterStateTaskExecutor.TaskResult> executionResults) {
+            this.taskInputs = taskInputs;
+            this.previousClusterState = previousClusterState;
+            this.newClusterState = newClusterState;
+            this.nonFailedTasks = nonFailedTasks;
+            this.executionResults = executionResults;
+        }
+
+        public void publishingFailed(Discovery.FailedToCommitClusterStateException t) {
+            nonFailedTasks.forEach(task -> task.listener.onFailure(task.source(), t));
+        }
+
+        public void processedDifferentClusterState(ClusterState previousClusterState, ClusterState newClusterState) {
+            nonFailedTasks.forEach(task -> task.listener.clusterStateProcessed(task.source(), previousClusterState, newClusterState));
+        }
+
+        public void clusterStatePublished(ClusterChangedEvent clusterChangedEvent) {
+            taskInputs.executor.clusterStatePublished(clusterChangedEvent);
+        }
+
+        public Discovery.AckListener createAckListener(ThreadPool threadPool, ClusterState newClusterState) {
+            ArrayList<Discovery.AckListener> ackListeners = new ArrayList<>();
+
+            //timeout straightaway, otherwise we could wait forever as the timeout thread has not started
+            nonFailedTasks.stream().filter(task -> task.listener instanceof AckedClusterStateTaskListener).forEach(task -> {
+                final AckedClusterStateTaskListener ackedListener = (AckedClusterStateTaskListener) task.listener;
+                if (ackedListener.ackTimeout() == null || ackedListener.ackTimeout().millis() == 0) {
+                    ackedListener.onAckTimeout();
+                } else {
+                    try {
+                        ackListeners.add(new AckCountDownListener(ackedListener, newClusterState.version(), newClusterState.nodes(),
+                            threadPool));
+                    } catch (EsRejectedExecutionException ex) {
+                        if (logger.isDebugEnabled()) {
+                            logger.debug("Couldn't schedule timeout thread - node might be shutting down", ex);
+                        }
+                        //timeout straightaway, otherwise we could wait forever as the timeout thread has not started
+                        ackedListener.onAckTimeout();
+                    }
+                }
+            });
+
+            return new DelegetingAckListener(ackListeners);
+        }
+
+        public boolean clusterStateUnchanged() {
+            return previousClusterState == newClusterState;
+        }
+
+        public void notifyFailedTasks() {
+            // fail all tasks that have failed
+            for (Batcher.UpdateTask updateTask : taskInputs.updateTasks) {
+                assert executionResults.containsKey(updateTask.task) : "missing " + updateTask;
+                final ClusterStateTaskExecutor.TaskResult taskResult = executionResults.get(updateTask.task);
+                if (taskResult.isSuccess() == false) {
+                    updateTask.listener.onFailure(updateTask.source(), taskResult.getFailure());
+                }
+            }
+        }
+
+        public void notifySuccessfulTasksOnUnchangedClusterState() {
+            nonFailedTasks.forEach(task -> {
+                if (task.listener instanceof AckedClusterStateTaskListener) {
+                    //no need to wait for ack if nothing changed, the update can be counted as acknowledged
+                    ((AckedClusterStateTaskListener) task.listener).onAllNodesAcked(null);
+                }
+                task.listener.clusterStateProcessed(task.source(), newClusterState, newClusterState);
+            });
+        }
+    }
+
+    /**
+     * Returns the tasks that are pending.
+     */
+    public List<PendingClusterTask> pendingTasks() {
+        return Arrays.stream(threadPoolExecutor.getPending()).map(pending -> {
+            assert pending.task instanceof SourcePrioritizedRunnable :
+                "thread pool executor should only use SourcePrioritizedRunnable instances but found: " + pending.task.getClass().getName();
+            SourcePrioritizedRunnable task = (SourcePrioritizedRunnable) pending.task;
+            return new PendingClusterTask(pending.insertionOrder, pending.priority, new Text(task.source()),
+                task.getAgeInMillis(), pending.executing);
+        }).collect(Collectors.toList());
+    }
+
+    /**
+     * Returns the number of currently pending tasks.
+     */
+    public int numberOfPendingTasks() {
+        return threadPoolExecutor.getNumberOfPendingTasks();
+    }
+
+    /**
+     * Returns the maximum wait time for tasks in the queue
+     *
+     * @return A zero time value if the queue is empty, otherwise the time value oldest task waiting in the queue
+     */
+    public TimeValue getMaxTaskWaitTime() {
+        return threadPoolExecutor.getMaxTaskWaitTime();
+    }
+
+    private SafeClusterStateTaskListener safe(ClusterStateTaskListener listener) {
+        if (listener instanceof AckedClusterStateTaskListener) {
+            return new SafeAckedClusterStateTaskListener((AckedClusterStateTaskListener) listener, logger);
+        } else {
+            return new SafeClusterStateTaskListener(listener, logger);
+        }
+    }
+
+    private static class SafeClusterStateTaskListener implements ClusterStateTaskListener {
+        private final ClusterStateTaskListener listener;
+        private final Logger logger;
+
+        SafeClusterStateTaskListener(ClusterStateTaskListener listener, Logger logger) {
+            this.listener = listener;
+            this.logger = logger;
+        }
+
+        @Override
+        public void onFailure(String source, Exception e) {
+            try {
+                listener.onFailure(source, e);
+            } catch (Exception inner) {
+                inner.addSuppressed(e);
+                logger.error(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "exception thrown by listener notifying of failure from [{}]", source), inner);
+            }
+        }
+
+        @Override
+        public void onNoLongerMaster(String source) {
+            try {
+                listener.onNoLongerMaster(source);
+            } catch (Exception e) {
+                logger.error(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "exception thrown by listener while notifying no longer master from [{}]", source), e);
+            }
+        }
+
+        @Override
+        public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+            try {
+                listener.clusterStateProcessed(source, oldState, newState);
+            } catch (Exception e) {
+                logger.error(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "exception thrown by listener while notifying of cluster state processed from [{}], old cluster state:\n" +
+                            "{}\nnew cluster state:\n{}",
+                        source, oldState, newState),
+                    e);
+            }
+        }
+    }
+
+    private static class SafeAckedClusterStateTaskListener extends SafeClusterStateTaskListener implements AckedClusterStateTaskListener {
+        private final AckedClusterStateTaskListener listener;
+        private final Logger logger;
+
+        SafeAckedClusterStateTaskListener(AckedClusterStateTaskListener listener, Logger logger) {
+            super(listener, logger);
+            this.listener = listener;
+            this.logger = logger;
+        }
+
+        @Override
+        public boolean mustAck(DiscoveryNode discoveryNode) {
+            return listener.mustAck(discoveryNode);
+        }
+
+        @Override
+        public void onAllNodesAcked(@Nullable Exception e) {
+            try {
+                listener.onAllNodesAcked(e);
+            } catch (Exception inner) {
+                inner.addSuppressed(e);
+                logger.error("exception thrown by listener while notifying on all nodes acked", inner);
+            }
+        }
+
+        @Override
+        public void onAckTimeout() {
+            try {
+                listener.onAckTimeout();
+            } catch (Exception e) {
+                logger.error("exception thrown by listener while notifying on ack timeout", e);
+            }
+        }
+
+        @Override
+        public TimeValue ackTimeout() {
+            return listener.ackTimeout();
+        }
+    }
+
+    protected void warnAboutSlowTaskIfNeeded(TimeValue executionTime, String source) {
+        if (executionTime.getMillis() > slowTaskLoggingThreshold.getMillis()) {
+            logger.warn("cluster state update task [{}] took [{}] above the warn threshold of {}", source, executionTime,
+                slowTaskLoggingThreshold);
+        }
+    }
+
+    private static class DelegetingAckListener implements Discovery.AckListener {
+
+        private final List<Discovery.AckListener> listeners;
+
+        private DelegetingAckListener(List<Discovery.AckListener> listeners) {
+            this.listeners = listeners;
+        }
+
+        @Override
+        public void onNodeAck(DiscoveryNode node, @Nullable Exception e) {
+            for (Discovery.AckListener listener : listeners) {
+                listener.onNodeAck(node, e);
+            }
+        }
+
+        @Override
+        public void onTimeout() {
+            throw new UnsupportedOperationException("no timeout delegation");
+        }
+    }
+
+    private static class AckCountDownListener implements Discovery.AckListener {
+
+        private static final Logger logger = Loggers.getLogger(AckCountDownListener.class);
+
+        private final AckedClusterStateTaskListener ackedTaskListener;
+        private final CountDown countDown;
+        private final DiscoveryNodes nodes;
+        private final long clusterStateVersion;
+        private final Future<?> ackTimeoutCallback;
+        private Exception lastFailure;
+
+        AckCountDownListener(AckedClusterStateTaskListener ackedTaskListener, long clusterStateVersion, DiscoveryNodes nodes,
+                             ThreadPool threadPool) {
+            this.ackedTaskListener = ackedTaskListener;
+            this.clusterStateVersion = clusterStateVersion;
+            this.nodes = nodes;
+            int countDown = 0;
+            for (DiscoveryNode node : nodes) {
+                if (ackedTaskListener.mustAck(node)) {
+                    countDown++;
+                }
+            }
+            //we always wait for at least 1 node (the master)
+            countDown = Math.max(1, countDown);
+            logger.trace("expecting {} acknowledgements for cluster_state update (version: {})", countDown, clusterStateVersion);
+            this.countDown = new CountDown(countDown);
+            this.ackTimeoutCallback = threadPool.schedule(ackedTaskListener.ackTimeout(), ThreadPool.Names.GENERIC, () -> onTimeout());
+        }
+
+        @Override
+        public void onNodeAck(DiscoveryNode node, @Nullable Exception e) {
+            if (!ackedTaskListener.mustAck(node)) {
+                //we always wait for the master ack anyway
+                if (!node.equals(nodes.getMasterNode())) {
+                    return;
+                }
+            }
+            if (e == null) {
+                logger.trace("ack received from node [{}], cluster_state update (version: {})", node, clusterStateVersion);
+            } else {
+                this.lastFailure = e;
+                logger.debug(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "ack received from node [{}], cluster_state update (version: {})", node, clusterStateVersion),
+                    e);
+            }
+
+            if (countDown.countDown()) {
+                logger.trace("all expected nodes acknowledged cluster_state update (version: {})", clusterStateVersion);
+                FutureUtils.cancel(ackTimeoutCallback);
+                ackedTaskListener.onAllNodesAcked(lastFailure);
+            }
+        }
+
+        @Override
+        public void onTimeout() {
+            if (countDown.fastForward()) {
+                logger.trace("timeout waiting for acknowledgement for cluster_state update (version: {})", clusterStateVersion);
+                ackedTaskListener.onAckTimeout();
+            }
+        }
+    }
+
+    protected ClusterTasksResult<Object> executeTasks(TaskInputs taskInputs, long startTimeNS, ClusterState previousClusterState) {
+        ClusterTasksResult<Object> clusterTasksResult;
+        try {
+            List<Object> inputs = taskInputs.updateTasks.stream().map(tUpdateTask -> tUpdateTask.task).collect(Collectors.toList());
+            clusterTasksResult = taskInputs.executor.execute(previousClusterState, inputs);
+            if (previousClusterState != clusterTasksResult.resultingState &&
+                previousClusterState.nodes().isLocalNodeElectedMaster() &&
+                (clusterTasksResult.resultingState.nodes().isLocalNodeElectedMaster() == false)) {
+                throw new AssertionError("update task submitted to MasterService cannot remove master");
+            }
+        } catch (Exception e) {
+            TimeValue executionTime = TimeValue.timeValueMillis(Math.max(0, TimeValue.nsecToMSec(currentTimeInNanos() - startTimeNS)));
+            if (logger.isTraceEnabled()) {
+                logger.trace(
+                    (Supplier<?>) () -> new ParameterizedMessage(
+                        "failed to execute cluster state update in [{}], state:\nversion [{}], source [{}]\n{}{}{}",
+                        executionTime,
+                        previousClusterState.version(),
+                        taskInputs.summary,
+                        previousClusterState.nodes(),
+                        previousClusterState.routingTable(),
+                        previousClusterState.getRoutingNodes()),
+                    e);
+            }
+            warnAboutSlowTaskIfNeeded(executionTime, taskInputs.summary);
+            clusterTasksResult = ClusterTasksResult.builder()
+                .failures(taskInputs.updateTasks.stream().map(updateTask -> updateTask.task)::iterator, e)
+                .build(previousClusterState);
+        }
+
+        assert clusterTasksResult.executionResults != null;
+        assert clusterTasksResult.executionResults.size() == taskInputs.updateTasks.size()
+            : String.format(Locale.ROOT, "expected [%d] task result%s but was [%d]", taskInputs.updateTasks.size(),
+            taskInputs.updateTasks.size() == 1 ? "" : "s", clusterTasksResult.executionResults.size());
+        boolean assertsEnabled = false;
+        assert (assertsEnabled = true);
+        if (assertsEnabled) {
+            ClusterTasksResult<Object> finalClusterTasksResult = clusterTasksResult;
+            taskInputs.updateTasks.forEach(updateTask -> {
+                assert finalClusterTasksResult.executionResults.containsKey(updateTask.task) :
+                    "missing task result for " + updateTask;
+            });
+        }
+
+        return clusterTasksResult;
+    }
+
+    public List<Batcher.UpdateTask> getNonFailedTasks(TaskInputs taskInputs,
+                                                      ClusterTasksResult<Object> clusterTasksResult) {
+        return taskInputs.updateTasks.stream().filter(updateTask -> {
+            assert clusterTasksResult.executionResults.containsKey(updateTask.task) : "missing " + updateTask;
+            final ClusterStateTaskExecutor.TaskResult taskResult =
+                clusterTasksResult.executionResults.get(updateTask.task);
+            return taskResult.isSuccess();
+        }).collect(Collectors.toList());
+    }
+
+    /**
+     * Represents a set of tasks to be processed together with their executor
+     */
+    protected class TaskInputs {
+        public final String summary;
+        public final List<Batcher.UpdateTask> updateTasks;
+        public final ClusterStateTaskExecutor<Object> executor;
+
+        TaskInputs(ClusterStateTaskExecutor<Object> executor, List<Batcher.UpdateTask> updateTasks, String summary) {
+            this.summary = summary;
+            this.executor = executor;
+            this.updateTasks = updateTasks;
+        }
+
+        public boolean runOnlyWhenMaster() {
+            return executor.runOnlyOnMaster();
+        }
+
+        public void onNoLongerMaster() {
+            updateTasks.forEach(task -> task.listener.onNoLongerMaster(task.source()));
+        }
+    }
+
+    /**
+     * Submits a batch of cluster state update tasks; submitted updates are guaranteed to be processed together,
+     * potentially with more tasks of the same executor.
+     *
+     * @param source   the source of the cluster state update task
+     * @param tasks    a map of update tasks and their corresponding listeners
+     * @param config   the cluster state update task configuration
+     * @param executor the cluster state update task executor; tasks
+     *                 that share the same executor will be executed
+     *                 batches on this executor
+     * @param <T>      the type of the cluster state update task state
+     *
+     */
+    public <T> void submitStateUpdateTasks(final String source,
+                                           final Map<T, ClusterStateTaskListener> tasks, final ClusterStateTaskConfig config,
+                                           final ClusterStateTaskExecutor<T> executor) {
+        if (!lifecycle.started()) {
+            return;
+        }
+        try {
+            List<Batcher.UpdateTask> safeTasks = tasks.entrySet().stream()
+                .map(e -> taskBatcher.new UpdateTask(config.priority(), source, e.getKey(), safe(e.getValue()), executor))
+                .collect(Collectors.toList());
+            taskBatcher.submitTasks(safeTasks, config.timeout());
+        } catch (EsRejectedExecutionException e) {
+            // ignore cases where we are shutting down..., there is really nothing interesting
+            // to be done here...
+            if (!lifecycle.stoppedOrClosed()) {
+                throw e;
+            }
+        }
+    }
+
+    // this one is overridden in tests so we can control time
+    protected long currentTimeInNanos() {
+        return System.nanoTime();
+    }
+}

core/src/main/java/org/elasticsearch/common/Randomness.java

@@ -41,7 +41,7 @@ import java.util.concurrent.ThreadLocalRandom;
  * setting a reproducible seed. When running the Elasticsearch server
  * process, non-reproducible sources of randomness are provided (unless
  * a setting is provided for a module that exposes a seed setting (e.g.,
- * DiscoveryService#NODE_ID_SEED_SETTING)).
+ * NodeEnvironment#NODE_ID_SEED_SETTING)).
  */
 public final class Randomness {
     private static final Method currentMethod;

core/src/main/java/org/elasticsearch/common/util/concurrent/BaseFuture.java

@@ -19,7 +19,8 @@
 
 package org.elasticsearch.common.util.concurrent;
 
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplierService;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.Transports;
@@ -63,7 +64,8 @@ public abstract class BaseFuture<V> implements Future<V> {
         assert timeout <= 0 ||
             (Transports.assertNotTransportThread(BLOCKING_OP_REASON) &&
                 ThreadPool.assertNotScheduleThread(BLOCKING_OP_REASON) &&
-                ClusterService.assertNotClusterStateUpdateThread(BLOCKING_OP_REASON));
+                ClusterApplierService.assertNotClusterStateUpdateThread(BLOCKING_OP_REASON) &&
+                MasterService.assertNotMasterUpdateThread(BLOCKING_OP_REASON));
         return sync.get(unit.toNanos(timeout));
     }
 
@@ -87,7 +89,8 @@ public abstract class BaseFuture<V> implements Future<V> {
     public V get() throws InterruptedException, ExecutionException {
         assert Transports.assertNotTransportThread(BLOCKING_OP_REASON) &&
             ThreadPool.assertNotScheduleThread(BLOCKING_OP_REASON) &&
-            ClusterService.assertNotClusterStateUpdateThread(BLOCKING_OP_REASON);
+            ClusterApplierService.assertNotClusterStateUpdateThread(BLOCKING_OP_REASON) &&
+            MasterService.assertNotMasterUpdateThread(BLOCKING_OP_REASON);
         return sync.get();
     }
 

core/src/main/java/org/elasticsearch/discovery/Discovery.java

@@ -21,6 +21,7 @@ package org.elasticsearch.discovery;
 
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
 import org.elasticsearch.common.Nullable;
@@ -36,10 +37,6 @@ import java.io.IOException;
  */
 public interface Discovery extends LifecycleComponent {
 
-    DiscoveryNode localNode();
-
-    String nodeDescription();
-
     /**
      * Another hack to solve dep injection problem..., note, this will be called before
      * any start is called.
@@ -48,7 +45,7 @@ public interface Discovery extends LifecycleComponent {
 
     /**
      * Publish all the changes to the cluster from the master (can be called just by the master). The publish
-     * process should not publish this state to the master as well! (the master is sending it...).
+     * process should apply this state to the master as well!
      *
      * The {@link AckListener} allows to keep track of the ack received from nodes, and verify whether
      * they updated their own cluster state or not.
@@ -58,6 +55,18 @@ public interface Discovery extends LifecycleComponent {
      */
     void publish(ClusterChangedEvent clusterChangedEvent, AckListener ackListener);
 
+    /**
+     * Returns the initial cluster state provided by the discovery module. Used by
+     * {@link org.elasticsearch.cluster.service.ClusterApplierService} as initial applied state.
+     */
+    ClusterState getInitialClusterState();
+
+    /**
+     * Returns latest cluster state used by the discovery module. Used by {@link org.elasticsearch.cluster.service.MasterService} to
+     * calculate the next prospective state to publish.
+     */
+    ClusterState clusterState();
+
     interface AckListener {
         void onNodeAck(DiscoveryNode node, @Nullable Exception e);
         void onTimeout();
@@ -83,8 +92,6 @@ public interface Discovery extends LifecycleComponent {
      */
     DiscoveryStats stats();
 
-    DiscoverySettings getDiscoverySettings();
-
     /**
      * Triggers the first join cycle
      */

core/src/main/java/org/elasticsearch/discovery/DiscoveryModule.java

@@ -19,10 +19,12 @@
 
 package org.elasticsearch.discovery;
 
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Setting.Property;
 import org.elasticsearch.common.settings.Settings;
@@ -55,8 +57,8 @@ public class DiscoveryModule {
     private final Discovery discovery;
 
     public DiscoveryModule(Settings settings, ThreadPool threadPool, TransportService transportService,
-                           NamedWriteableRegistry namedWriteableRegistry, NetworkService networkService, ClusterService clusterService,
+                           NamedWriteableRegistry namedWriteableRegistry, NetworkService networkService, MasterService masterService,
-                           List<DiscoveryPlugin> plugins) {
+                           ClusterApplier clusterApplier, ClusterSettings clusterSettings, List<DiscoveryPlugin> plugins) {
         final UnicastHostsProvider hostsProvider;
 
         Map<String, Supplier<UnicastHostsProvider>> hostProviders = new HashMap<>();
@@ -80,12 +82,13 @@ public class DiscoveryModule {
 
         Map<String, Supplier<Discovery>> discoveryTypes = new HashMap<>();
         discoveryTypes.put("zen",
-            () -> new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider));
+            () -> new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, masterService, clusterApplier,
-        discoveryTypes.put("none", () -> new NoneDiscovery(settings, clusterService, clusterService.getClusterSettings()));
+                clusterSettings, hostsProvider));
-        discoveryTypes.put("single-node", () -> new SingleNodeDiscovery(settings, clusterService));
+        discoveryTypes.put("tribe", () -> new TribeDiscovery(settings, transportService, clusterApplier));
+        discoveryTypes.put("single-node", () -> new SingleNodeDiscovery(settings, transportService, clusterApplier));
         for (DiscoveryPlugin plugin : plugins) {
             plugin.getDiscoveryTypes(threadPool, transportService, namedWriteableRegistry,
-                clusterService, hostsProvider).entrySet().forEach(entry -> {
+                masterService, clusterApplier, clusterSettings, hostsProvider).entrySet().forEach(entry -> {
                 if (discoveryTypes.put(entry.getKey(), entry.getValue()) != null) {
                     throw new IllegalArgumentException("Cannot register discovery type [" + entry.getKey() + "] twice");
                 }

core/src/main/java/org/elasticsearch/discovery/NoneDiscovery.java

@@ -1,102 +0,0 @@
-/*
- * Licensed to Elasticsearch under one or more contributor
- * license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright
- * ownership. Elasticsearch licenses this file to you under
- * the Apache License, Version 2.0 (the "License"); you may
- * not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-package org.elasticsearch.discovery;
-
-import org.elasticsearch.cluster.ClusterChangedEvent;
-import org.elasticsearch.cluster.node.DiscoveryNode;
-import org.elasticsearch.cluster.routing.allocation.AllocationService;
-import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.common.component.AbstractLifecycleComponent;
-import org.elasticsearch.common.inject.Inject;
-import org.elasticsearch.common.settings.ClusterSettings;
-import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.discovery.zen.ElectMasterService;
-
-/**
- * A {@link Discovery} implementation that is used by {@link org.elasticsearch.tribe.TribeService}. This implementation
- * doesn't support any clustering features. Most notably {@link #startInitialJoin()} does nothing and
- * {@link #publish(ClusterChangedEvent, AckListener)} is not supported.
- */
-public class NoneDiscovery extends AbstractLifecycleComponent implements Discovery {
-
-    private final ClusterService clusterService;
-    private final DiscoverySettings discoverySettings;
-
-    @Inject
-    public NoneDiscovery(Settings settings, ClusterService clusterService, ClusterSettings clusterSettings) {
-        super(settings);
-        this.clusterService = clusterService;
-        this.discoverySettings = new DiscoverySettings(settings, clusterSettings);
-    }
-
-    @Override
-    public DiscoveryNode localNode() {
-        return clusterService.localNode();
-    }
-
-    @Override
-    public String nodeDescription() {
-        return clusterService.getClusterName().value() + "/" + clusterService.localNode().getId();
-    }
-
-    @Override
-    public void setAllocationService(AllocationService allocationService) {
-
-    }
-
-    @Override
-    public void publish(ClusterChangedEvent clusterChangedEvent, AckListener ackListener) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public DiscoveryStats stats() {
-        return null;
-    }
-
-    @Override
-    public DiscoverySettings getDiscoverySettings() {
-        return discoverySettings;
-    }
-
-    @Override
-    public void startInitialJoin() {
-
-    }
-
-    @Override
-    public int getMinimumMasterNodes() {
-        return ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING.get(settings);
-    }
-
-    @Override
-    protected void doStart() {
-
-    }
-
-    @Override
-    protected void doStop() {
-
-    }
-
-    @Override
-    protected void doClose() {
-
-    }
-}

core/src/main/java/org/elasticsearch/discovery/TribeDiscovery.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.discovery;
+
+import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterName;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.block.ClusterBlocks;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.discovery.single.SingleNodeDiscovery;
+import org.elasticsearch.transport.TransportService;
+
+import static org.elasticsearch.tribe.TribeService.BLOCKS_METADATA_SETTING;
+import static org.elasticsearch.tribe.TribeService.BLOCKS_WRITE_SETTING;
+import static org.elasticsearch.tribe.TribeService.TRIBE_METADATA_BLOCK;
+import static org.elasticsearch.tribe.TribeService.TRIBE_WRITE_BLOCK;
+
+/**
+ * A {@link Discovery} implementation that is used by {@link org.elasticsearch.tribe.TribeService}. This implementation
+ * doesn't support any clustering features. Most notably {@link #startInitialJoin()} does nothing and
+ * {@link #publish(ClusterChangedEvent, AckListener)} delegates state updates directly to the
+ * {@link org.elasticsearch.cluster.service.ClusterApplierService}.
+ */
+public class TribeDiscovery extends SingleNodeDiscovery implements Discovery {
+
+    @Inject
+    public TribeDiscovery(Settings settings, TransportService transportService, ClusterApplier clusterApplier) {
+        super(settings, transportService, clusterApplier);
+    }
+
+    @Override
+    public synchronized ClusterState getInitialClusterState() {
+        if (initialState == null) {
+            ClusterBlocks.Builder clusterBlocks = ClusterBlocks.builder(); // don't add no_master / state recovery block
+            if (BLOCKS_WRITE_SETTING.get(settings)) {
+                clusterBlocks.addGlobalBlock(TRIBE_WRITE_BLOCK);
+            }
+            if (BLOCKS_METADATA_SETTING.get(settings)) {
+                clusterBlocks.addGlobalBlock(TRIBE_METADATA_BLOCK);
+            }
+            DiscoveryNode localNode = transportService.getLocalNode();
+            initialState = ClusterState.builder(ClusterName.CLUSTER_NAME_SETTING.get(settings))
+                .nodes(DiscoveryNodes.builder().add(localNode).localNodeId(localNode.getId()).build())
+                .blocks(clusterBlocks).build();
+        }
+        return initialState;
+    }
+
+    @Override
+    public synchronized void startInitialJoin() {
+        // no state recovery required as tribe nodes don't persist cluster state
+    }
+}

core/src/main/java/org/elasticsearch/discovery/single/SingleNodeDiscovery.java

@@ -19,53 +19,44 @@
 
 package org.elasticsearch.discovery.single;
 
+import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.ClusterStateTaskConfig;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
-import org.elasticsearch.cluster.ClusterStateTaskExecutor;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
-import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.component.AbstractLifecycleComponent;
-import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
-import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.discovery.DiscoveryStats;
 import org.elasticsearch.discovery.zen.PendingClusterStateStats;
-import org.elasticsearch.discovery.zen.PendingClusterStatesQueue;
+import org.elasticsearch.transport.TransportService;
 
 import java.io.IOException;
-import java.util.Collections;
-import java.util.List;
 import java.util.Objects;
+import java.util.concurrent.CountDownLatch;
+
+import static org.elasticsearch.gateway.GatewayService.STATE_NOT_RECOVERED_BLOCK;
 
 /**
  * A discovery implementation where the only member of the cluster is the local node.
  */
 public class SingleNodeDiscovery extends AbstractLifecycleComponent implements Discovery {
 
-    private final ClusterService clusterService;
+    protected final TransportService transportService;
-    private final DiscoverySettings discoverySettings;
+    private final ClusterApplier clusterApplier;
+    protected volatile ClusterState initialState;
+    private volatile ClusterState clusterState;
 
-    public SingleNodeDiscovery(final Settings settings, final ClusterService clusterService) {
+    public SingleNodeDiscovery(final Settings settings, final TransportService transportService,
+                               ClusterApplier clusterApplier) {
         super(Objects.requireNonNull(settings));
-        this.clusterService = Objects.requireNonNull(clusterService);
+        this.transportService = Objects.requireNonNull(transportService);
-        final ClusterSettings clusterSettings =
+        this.clusterApplier = clusterApplier;
-                Objects.requireNonNull(clusterService.getClusterSettings());
-        this.discoverySettings = new DiscoverySettings(settings, clusterSettings);
-    }
-
-    @Override
-    public DiscoveryNode localNode() {
-        return clusterService.localNode();
-    }
-
-    @Override
-    public String nodeDescription() {
-        return clusterService.getClusterName().value() + "/" + clusterService.localNode().getId();
     }
 
     @Override
@@ -74,8 +65,57 @@ public class SingleNodeDiscovery extends AbstractLifecycleComponent implements D
     }
 
     @Override
-    public void publish(final ClusterChangedEvent event, final AckListener listener) {
+    public synchronized void publish(final ClusterChangedEvent event,
+                                     final AckListener ackListener) {
+        clusterState = event.state();
+        CountDownLatch latch = new CountDownLatch(1);
 
+        ClusterStateTaskListener listener = new ClusterStateTaskListener() {
+            @Override
+            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                latch.countDown();
+                ackListener.onNodeAck(transportService.getLocalNode(), null);
+            }
+
+            @Override
+            public void onFailure(String source, Exception e) {
+                latch.countDown();
+                ackListener.onNodeAck(transportService.getLocalNode(), e);
+                logger.warn(
+                    (org.apache.logging.log4j.util.Supplier<?>) () -> new ParameterizedMessage(
+                        "failed while applying cluster state locally [{}]",
+                        event.source()),
+                    e);
+            }
+        };
+        clusterApplier.onNewClusterState("apply-locally-on-node[" + event.source() + "]", this::clusterState, listener);
+
+        try {
+            latch.await();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+
+    @Override
+    public synchronized ClusterState getInitialClusterState() {
+        if (initialState == null) {
+            DiscoveryNode localNode = transportService.getLocalNode();
+            initialState = ClusterState.builder(ClusterName.CLUSTER_NAME_SETTING.get(settings))
+                .nodes(DiscoveryNodes.builder().add(localNode)
+                    .localNodeId(localNode.getId())
+                    .masterNodeId(localNode.getId())
+                    .build())
+                .blocks(ClusterBlocks.builder()
+                    .addGlobalBlock(STATE_NOT_RECOVERED_BLOCK))
+                .build();
+        }
+        return initialState;
+    }
+
+    @Override
+    public ClusterState clusterState() {
+        return clusterState;
     }
 
     @Override
@@ -84,41 +124,11 @@ public class SingleNodeDiscovery extends AbstractLifecycleComponent implements D
     }
 
     @Override
-    public DiscoverySettings getDiscoverySettings() {
+    public synchronized void startInitialJoin() {
-        return discoverySettings;
+        // apply a fresh cluster state just so that state recovery gets triggered by GatewayService
-    }
+        // TODO: give discovery module control over GatewayService
-
+        clusterState = ClusterState.builder(getInitialClusterState()).build();
-    @Override
+        clusterApplier.onNewClusterState("single-node-start-initial-join", this::clusterState, (source, e) -> {});
-    public void startInitialJoin() {
-        final ClusterStateTaskExecutor<DiscoveryNode> executor =
-                new ClusterStateTaskExecutor<DiscoveryNode>() {
-
-                    @Override
-                    public ClusterTasksResult<DiscoveryNode> execute(
-                            final ClusterState current,
-                            final List<DiscoveryNode> tasks) throws Exception {
-                        assert tasks.size() == 1;
-                        final DiscoveryNodes.Builder nodes =
-                                DiscoveryNodes.builder(current.nodes());
-                        // always set the local node as master, there will not be other nodes
-                        nodes.masterNodeId(localNode().getId());
-                        final ClusterState next =
-                                ClusterState.builder(current).nodes(nodes).build();
-                        final ClusterTasksResult.Builder<DiscoveryNode> result =
-                                ClusterTasksResult.builder();
-                        return result.successes(tasks).build(next);
-                    }
-
-                    @Override
-                    public boolean runOnlyOnMaster() {
-                        return false;
-                    }
-
-                };
-        final ClusterStateTaskConfig config = ClusterStateTaskConfig.build(Priority.URGENT);
-        clusterService.submitStateUpdateTasks(
-                "single-node-start-initial-join",
-                Collections.singletonMap(localNode(), (s, e) -> {}), config, executor);
     }
 
     @Override
@@ -127,8 +137,9 @@ public class SingleNodeDiscovery extends AbstractLifecycleComponent implements D
     }
 
     @Override
-    protected void doStart() {
+    protected synchronized void doStart() {
-
+        initialState = getInitialClusterState();
+        clusterState = initialState;
     }
 
     @Override

core/src/main/java/org/elasticsearch/discovery/zen/MasterFaultDetection.java

@@ -28,7 +28,7 @@ import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.NotMasterException;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -64,7 +64,8 @@ public class MasterFaultDetection extends FaultDetection {
 
     }
 
-    private final ClusterService clusterService;
+    private final MasterService masterService;
+    private final java.util.function.Supplier<ClusterState> clusterStateSupplier;
     private final CopyOnWriteArrayList<Listener> listeners = new CopyOnWriteArrayList<>();
 
     private volatile MasterPinger masterPinger;
@@ -78,9 +79,11 @@ public class MasterFaultDetection extends FaultDetection {
     private final AtomicBoolean notifiedMasterFailure = new AtomicBoolean();
 
     public MasterFaultDetection(Settings settings, ThreadPool threadPool, TransportService transportService,
-                                ClusterService clusterService) {
+                                java.util.function.Supplier<ClusterState> clusterStateSupplier, MasterService masterService,
-        super(settings, threadPool, transportService, clusterService.getClusterName());
+                                ClusterName clusterName) {
-        this.clusterService = clusterService;
+        super(settings, threadPool, transportService, clusterName);
+        this.clusterStateSupplier = clusterStateSupplier;
+        this.masterService = masterService;
 
         logger.debug("[master] uses ping_interval [{}], ping_timeout [{}], ping_retries [{}]", pingInterval, pingRetryTimeout,
             pingRetryCount);
@@ -215,7 +218,8 @@ public class MasterFaultDetection extends FaultDetection {
                 return;
             }
 
-            final MasterPingRequest request = new MasterPingRequest(clusterService.localNode(), masterToPing, clusterName);
+            final MasterPingRequest request = new MasterPingRequest(
+                clusterStateSupplier.get().nodes().getLocalNode(), masterToPing, clusterName);
             final TransportRequestOptions options = TransportRequestOptions.builder().withType(TransportRequestOptions.Type.PING)
                 .withTimeout(pingRetryTimeout).build();
             transportService.sendRequest(masterToPing, MASTER_PING_ACTION_NAME, request, options,
@@ -323,7 +327,7 @@ public class MasterFaultDetection extends FaultDetection {
 
         @Override
         public void messageReceived(final MasterPingRequest request, final TransportChannel channel) throws Exception {
-            final DiscoveryNodes nodes = clusterService.state().nodes();
+            final DiscoveryNodes nodes = clusterStateSupplier.get().nodes();
             // check if we are really the same master as the one we seemed to be think we are
             // this can happen if the master got "kill -9" and then another node started using the same port
             if (!request.masterNode.equals(nodes.getLocalNode())) {
@@ -348,7 +352,7 @@ public class MasterFaultDetection extends FaultDetection {
 
             if (!nodes.isLocalNodeElectedMaster() || !nodes.nodeExists(request.sourceNode)) {
                 logger.trace("checking ping from {} under a cluster state thread", request.sourceNode);
-                clusterService.submitStateUpdateTask("master ping (from: " + request.sourceNode + ")", new ClusterStateUpdateTask() {
+                masterService.submitStateUpdateTask("master ping (from: " + request.sourceNode + ")", new ClusterStateUpdateTask() {
 
                     @Override
                     public ClusterState execute(ClusterState currentState) throws Exception {

core/src/main/java/org/elasticsearch/discovery/zen/NodeJoinController.java

@@ -24,20 +24,21 @@ import org.apache.logging.log4j.util.Supplier;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterChangedEvent;
-import org.elasticsearch.cluster.ClusterStateTaskExecutor;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateTaskConfig;
+import org.elasticsearch.cluster.ClusterStateTaskExecutor;
 import org.elasticsearch.cluster.ClusterStateTaskListener;
 import org.elasticsearch.cluster.NotMasterException;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
-import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.transport.TransportAddress;
 import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.discovery.DiscoverySettings;
 
 import java.util.ArrayList;
@@ -55,7 +56,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
  */
 public class NodeJoinController extends AbstractComponent {
 
-    private final ClusterService clusterService;
+    private final MasterService masterService;
     private final AllocationService allocationService;
     private final ElectMasterService electMaster;
     private final JoinTaskExecutor joinTaskExecutor = new JoinTaskExecutor();
@@ -65,10 +66,10 @@ public class NodeJoinController extends AbstractComponent {
     private ElectionContext electionContext = null;
 
 
-    public NodeJoinController(ClusterService clusterService, AllocationService allocationService, ElectMasterService electMaster,
+    public NodeJoinController(MasterService masterService, AllocationService allocationService, ElectMasterService electMaster,
                               Settings settings) {
         super(settings);
-        this.clusterService = clusterService;
+        this.masterService = masterService;
         this.allocationService = allocationService;
         this.electMaster = electMaster;
     }
@@ -176,7 +177,7 @@ public class NodeJoinController extends AbstractComponent {
             electionContext.addIncomingJoin(node, callback);
             checkPendingJoinsAndElectIfNeeded();
         } else {
-            clusterService.submitStateUpdateTask("zen-disco-node-join",
+            masterService.submitStateUpdateTask("zen-disco-node-join",
                 node, ClusterStateTaskConfig.build(Priority.URGENT),
                 joinTaskExecutor, new JoinTaskListener(callback, logger));
         }
@@ -279,7 +280,7 @@ public class NodeJoinController extends AbstractComponent {
 
             tasks.put(BECOME_MASTER_TASK, (source1, e) -> {}); // noop listener, the election finished listener determines result
             tasks.put(FINISH_ELECTION_TASK, electionFinishedListener);
-            clusterService.submitStateUpdateTasks(source, tasks, ClusterStateTaskConfig.build(Priority.URGENT), joinTaskExecutor);
+            masterService.submitStateUpdateTasks(source, tasks, ClusterStateTaskConfig.build(Priority.URGENT), joinTaskExecutor);
         }
 
         public synchronized void closeAndProcessPending(String reason) {
@@ -287,7 +288,7 @@ public class NodeJoinController extends AbstractComponent {
             Map<DiscoveryNode, ClusterStateTaskListener> tasks = getPendingAsTasks();
             final String source = "zen-disco-election-stop [" + reason + "]";
             tasks.put(FINISH_ELECTION_TASK, electionFinishedListener);
-            clusterService.submitStateUpdateTasks(source, tasks, ClusterStateTaskConfig.build(Priority.URGENT), joinTaskExecutor);
+            masterService.submitStateUpdateTasks(source, tasks, ClusterStateTaskConfig.build(Priority.URGENT), joinTaskExecutor);
         }
 
         private void innerClose() {
@@ -307,7 +308,7 @@ public class NodeJoinController extends AbstractComponent {
         }
 
         private void onElectedAsMaster(ClusterState state) {
-            ClusterService.assertClusterStateThread();
+            assert MasterService.assertMasterUpdateThread();
             assert state.nodes().isLocalNodeElectedMaster() : "onElectedAsMaster called but local node is not master";
             ElectionCallback callback = getCallback(); // get under lock
             if (callback != null) {
@@ -316,7 +317,7 @@ public class NodeJoinController extends AbstractComponent {
         }
 
         private void onFailure(Throwable t) {
-            ClusterService.assertClusterStateThread();
+            assert MasterService.assertMasterUpdateThread();
             ElectionCallback callback = getCallback(); // get under lock
             if (callback != null) {
                 callback.onFailure(t);
@@ -469,6 +470,7 @@ public class NodeJoinController extends AbstractComponent {
             DiscoveryNodes currentNodes = currentState.nodes();
             DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(currentNodes);
             nodesBuilder.masterNodeId(currentState.nodes().getLocalNodeId());
+
             for (final DiscoveryNode joiningNode : joiningNodes) {
                 final DiscoveryNode nodeWithSameId = nodesBuilder.get(joiningNode.getId());
                 if (nodeWithSameId != null && nodeWithSameId.equals(joiningNode) == false) {
@@ -486,7 +488,9 @@ public class NodeJoinController extends AbstractComponent {
 
             // now trim any left over dead nodes - either left there when the previous master stepped down
             // or removed by us above
-            ClusterState tmpState = ClusterState.builder(currentState).nodes(nodesBuilder).build();
+            ClusterState tmpState = ClusterState.builder(currentState).nodes(nodesBuilder).blocks(ClusterBlocks.builder()
+                .blocks(currentState.blocks())
+                .removeGlobalBlock(DiscoverySettings.NO_MASTER_BLOCK_ID)).build();
             return ClusterState.builder(allocationService.deassociateDeadNodes(tmpState, false,
                 "removed dead nodes on election"));
         }

core/src/main/java/org/elasticsearch/discovery/zen/ZenDiscovery.java

@@ -31,28 +31,28 @@ import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateTaskConfig;
 import org.elasticsearch.cluster.ClusterStateTaskExecutor;
 import org.elasticsearch.cluster.ClusterStateTaskListener;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.NotMasterException;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.component.AbstractLifecycleComponent;
 import org.elasticsearch.common.component.Lifecycle;
-import org.elasticsearch.common.inject.internal.Nullable;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.lease.Releasables;
 import org.elasticsearch.common.logging.LoggerMessageFormat;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Setting.Property;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
-import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.discovery.DiscoveryStats;
@@ -68,8 +68,10 @@ import org.elasticsearch.transport.TransportService;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -78,6 +80,7 @@ import java.util.function.Consumer;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.common.unit.TimeValue.timeValueSeconds;
+import static org.elasticsearch.gateway.GatewayService.STATE_NOT_RECOVERED_BLOCK;
 
 public class ZenDiscovery extends AbstractLifecycleComponent implements Discovery, PingContextProvider {
 
@@ -105,8 +108,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
     public static final String DISCOVERY_REJOIN_ACTION_NAME = "internal:discovery/zen/rejoin";
 
     private final TransportService transportService;
-    private final NamedWriteableRegistry namedWriteableRegistry;
+    private final MasterService masterService;
-    private final ClusterService clusterService;
     private AllocationService allocationService;
     private final ClusterName clusterName;
     private final DiscoverySettings discoverySettings;
@@ -142,15 +144,19 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
     private volatile NodeJoinController nodeJoinController;
     private volatile NodeRemovalClusterStateTaskExecutor nodeRemovalExecutor;
 
+    private final ClusterApplier clusterApplier;
+    private final AtomicReference<ClusterState> state; // last committed cluster state
+    private final Object stateMutex = new Object();
+    private volatile ClusterState initialState; // set lazily when discovery layer is started
+
     public ZenDiscovery(Settings settings, ThreadPool threadPool, TransportService transportService,
-                        NamedWriteableRegistry namedWriteableRegistry,
+                        NamedWriteableRegistry namedWriteableRegistry, MasterService masterService, ClusterApplier clusterApplier,
-                        ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                        ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
         super(settings);
-        this.clusterService = clusterService;
+        this.masterService = masterService;
-        this.clusterName = clusterService.getClusterName();
+        this.clusterApplier = clusterApplier;
         this.transportService = transportService;
-        this.namedWriteableRegistry = namedWriteableRegistry;
+        this.discoverySettings = new DiscoverySettings(settings, clusterSettings);
-        this.discoverySettings = new DiscoverySettings(settings, clusterService.getClusterSettings());
         this.zenPing = newZenPing(settings, threadPool, transportService, hostsProvider);
         this.electMaster = new ElectMasterService(settings);
         this.pingTimeout = PING_TIMEOUT_SETTING.get(settings);
@@ -160,6 +166,8 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         this.maxPingsFromAnotherMaster = MAX_PINGS_FROM_ANOTHER_MASTER_SETTING.get(settings);
         this.sendLeaveRequest = SEND_LEAVE_REQUEST_SETTING.get(settings);
         this.threadPool = threadPool;
+        this.clusterName = ClusterName.CLUSTER_NAME_SETTING.get(settings);
+        this.state = new AtomicReference<>();
 
         this.masterElectionIgnoreNonMasters = MASTER_ELECTION_IGNORE_NON_MASTER_PINGS_SETTING.get(settings);
         this.masterElectionWaitForJoinsTimeout = MASTER_ELECTION_WAIT_FOR_JOINS_TIMEOUT_SETTING.get(settings);
@@ -167,9 +175,9 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         logger.debug("using ping_timeout [{}], join.timeout [{}], master_election.ignore_non_master [{}]",
                 this.pingTimeout, joinTimeout, masterElectionIgnoreNonMasters);
 
-        clusterService.getClusterSettings().addSettingsUpdateConsumer(ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING,
+        clusterSettings.addSettingsUpdateConsumer(ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING,
             this::handleMinimumMasterNodesChanged, (value) -> {
-                final ClusterState clusterState = clusterService.state();
+                final ClusterState clusterState = this.clusterState();
                 int masterNodes = clusterState.nodes().getMasterNodes().size();
                 // the purpose of this validation is to make sure that the master doesn't step down
                 // due to a change in master nodes, which also means that there is no way to revert
@@ -188,9 +196,9 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
                 }
         });
 
-        this.masterFD = new MasterFaultDetection(settings, threadPool, transportService, clusterService);
+        this.masterFD = new MasterFaultDetection(settings, threadPool, transportService, this::clusterState, masterService, clusterName);
         this.masterFD.addListener(new MasterNodeFailureListener());
-        this.nodesFD = new NodesFaultDetection(settings, threadPool, transportService, clusterService.getClusterName());
+        this.nodesFD = new NodesFaultDetection(settings, threadPool, transportService, clusterName);
         this.nodesFD.addListener(new NodeFaultDetectionListener());
 
         this.publishClusterState =
@@ -198,10 +206,10 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
                         settings,
                         transportService,
                         namedWriteableRegistry,
-                        clusterService::state,
+                        this::clusterState,
                         new NewPendingClusterStateListener(),
                         discoverySettings,
-                        clusterService.getClusterName());
+                        clusterName);
         this.membership = new MembershipAction(settings, transportService, new MembershipListener());
         this.joinThreadControl = new JoinThreadControl();
 
@@ -222,30 +230,26 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
 
     @Override
     protected void doStart() {
-        nodesFD.setLocalNode(clusterService.localNode());
+        DiscoveryNode localNode = transportService.getLocalNode();
+        assert localNode != null;
+        synchronized (stateMutex) {
+            initialState = getInitialClusterState();
+            state.set(initialState);
+            nodesFD.setLocalNode(localNode);
             joinThreadControl.start();
+        }
         zenPing.start(this);
-        this.nodeJoinController = new NodeJoinController(clusterService, allocationService, electMaster, settings);
+        this.nodeJoinController = new NodeJoinController(masterService, allocationService, electMaster, settings);
         this.nodeRemovalExecutor = new NodeRemovalClusterStateTaskExecutor(allocationService, electMaster, this::submitRejoin, logger);
     }
 
     @Override
     public void startInitialJoin() {
         // start the join thread from a cluster state update. See {@link JoinThreadControl} for details.
-        clusterService.submitStateUpdateTask("initial_join", new LocalClusterUpdateTask() {
+        synchronized (stateMutex) {
-
+            // do the join on a different thread, the caller of this method waits for 30s anyhow till it is discovered
-            @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
-                // do the join on a different thread, the DiscoveryService waits for 30s anyhow till it is discovered
             joinThreadControl.startNewThreadIfNotRunning();
-                return unchanged();
         }
-
-            @Override
-            public void onFailure(String source, @org.elasticsearch.common.Nullable Exception e) {
-                logger.warn("failed to start initial join process", e);
-            }
-        });
     }
 
     @Override
@@ -286,58 +290,122 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         IOUtils.close(masterFD, nodesFD);
     }
 
-    @Override
-    public DiscoveryNode localNode() {
-        return clusterService.localNode();
-    }
-
-    @Override
-    public String nodeDescription() {
-        return clusterName.value() + "/" + clusterService.localNode().getId();
-    }
-
     /** start of {@link PingContextProvider } implementation */
     @Override
     public DiscoveryNodes nodes() {
-        return clusterService.state().nodes();
+        return clusterState().nodes();
     }
 
     @Override
     public ClusterState clusterState() {
-        return clusterService.state();
+        ClusterState clusterState = state.get();
+        assert clusterState != null : "accessing cluster state before it is set";
+        return clusterState;
     }
 
     /** end of {@link PingContextProvider } implementation */
 
-
     @Override
     public void publish(ClusterChangedEvent clusterChangedEvent, AckListener ackListener) {
-        if (!clusterChangedEvent.state().getNodes().isLocalNodeElectedMaster()) {
+        ClusterState newState = clusterChangedEvent.state();
-            throw new IllegalStateException("Shouldn't publish state when not master");
+        assert newState.getNodes().isLocalNodeElectedMaster() : "Shouldn't publish state when not master " + clusterChangedEvent.source();
+
+        // state got changed locally (maybe because another master published to us)
+        if (clusterChangedEvent.previousState() != this.state.get()) {
+            throw new FailedToCommitClusterStateException("state was mutated while calculating new CS update");
         }
+
+        publishClusterState.pendingStatesQueue().addPending(newState);
+
         try {
             publishClusterState.publish(clusterChangedEvent, electMaster.minimumMasterNodes(), ackListener);
         } catch (FailedToCommitClusterStateException t) {
             // cluster service logs a WARN message
-            logger.debug("failed to publish cluster state version [{}] (not enough nodes acknowledged, min master nodes [{}])", clusterChangedEvent.state().version(), electMaster.minimumMasterNodes());
+            logger.debug("failed to publish cluster state version [{}] (not enough nodes acknowledged, min master nodes [{}])",
-            submitRejoin("zen-disco-failed-to-publish");
+                newState.version(), electMaster.minimumMasterNodes());
+
+            synchronized (stateMutex) {
+                publishClusterState.pendingStatesQueue().failAllStatesAndClear(
+                    new ElasticsearchException("failed to publish cluster state"));
+
+                rejoin("zen-disco-failed-to-publish");
+            }
             throw t;
         }
 
-        // update the set of nodes to ping after the new cluster state has been published
+        final DiscoveryNode localNode = newState.getNodes().getLocalNode();
-        nodesFD.updateNodesAndPing(clusterChangedEvent.state());
+        final CountDownLatch latch = new CountDownLatch(1);
+        final AtomicBoolean processedOrFailed = new AtomicBoolean();
+        publishClusterState.pendingStatesQueue().markAsCommitted(newState.stateUUID(),
+            new PendingClusterStatesQueue.StateProcessedListener() {
+                @Override
+                public void onNewClusterStateProcessed() {
+                    processedOrFailed.set(true);
+                    latch.countDown();
+                    ackListener.onNodeAck(localNode, null);
+                }
 
-        // clean the pending cluster queue - we are currently master, so any pending cluster state should be failed
+                @Override
-        // note that we also clean the queue on master failure (see handleMasterGone) but a delayed cluster state publish
+                public void onNewClusterStateFailed(Exception e) {
-        // from a stale master can still make it in the queue during the election (but not be committed)
+                    processedOrFailed.set(true);
-        publishClusterState.pendingStatesQueue().failAllStatesAndClear(new ElasticsearchException("elected as master"));
+                    latch.countDown();
+                    ackListener.onNodeAck(localNode, e);
+                    logger.warn(
+                        (org.apache.logging.log4j.util.Supplier<?>) () -> new ParameterizedMessage(
+                            "failed while applying cluster state locally [{}]",
+                            clusterChangedEvent.source()),
+                        e);
+                }
+            });
+
+        synchronized (stateMutex) {
+            if (clusterChangedEvent.previousState() != this.state.get()) {
+                throw new FailedToCommitClusterStateException("local state was mutated while CS update was published to other nodes");
+            }
+
+            boolean sentToApplier = processNextCommittedClusterState("master " + newState.nodes().getMasterNode() +
+                " committed version [" + newState.version() + "] source [" + clusterChangedEvent.source() + "]");
+            if (sentToApplier == false && processedOrFailed.get() == false) {
+                assert false : "cluster state published locally neither processed nor failed: " + newState;
+                logger.warn("cluster state with version [{}] that is published locally has neither been processed nor failed",
+                    newState.version());
+                return;
+            }
+        }
+        // indefinitely wait for cluster state to be applied locally
+        try {
+            latch.await();
+        } catch (InterruptedException e) {
+            logger.debug(
+                (org.apache.logging.log4j.util.Supplier<?>) () -> new ParameterizedMessage(
+                    "interrupted while applying cluster state locally [{}]",
+                    clusterChangedEvent.source()),
+                e);
+            Thread.currentThread().interrupt();
+        }
+    }
+
+    @Override
+    public synchronized ClusterState getInitialClusterState() {
+        if (initialState == null) {
+            assert state.get() == null;
+            DiscoveryNode localNode = transportService.getLocalNode();
+            assert localNode != null;
+            initialState = ClusterState.builder(clusterName)
+                .blocks(ClusterBlocks.builder()
+                    .addGlobalBlock(STATE_NOT_RECOVERED_BLOCK)
+                    .addGlobalBlock(discoverySettings.getNoMasterBlock()))
+                .nodes(DiscoveryNodes.builder().add(localNode).localNodeId(localNode.getId()))
+                .build();
+        }
+        return initialState;
     }
 
     /**
      * Gets the current set of nodes involved in the node fault detection.
      * NB: for testing purposes
      */
-    public Set<DiscoveryNode> getFaultDetectionNodes() {
+    Set<DiscoveryNode> getFaultDetectionNodes() {
         return nodesFD.getNodes();
     }
 
@@ -347,7 +415,6 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         return new DiscoveryStats(queueStats);
     }
 
-    @Override
     public DiscoverySettings getDiscoverySettings() {
         return discoverySettings;
     }
@@ -391,24 +458,26 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
             return;
         }
 
-        if (clusterService.localNode().equals(masterNode)) {
+        if (transportService.getLocalNode().equals(masterNode)) {
             final int requiredJoins = Math.max(0, electMaster.minimumMasterNodes() - 1); // we count as one
             logger.debug("elected as master, waiting for incoming joins ([{}] needed)", requiredJoins);
             nodeJoinController.waitToBeElectedAsMaster(requiredJoins, masterElectionWaitForJoinsTimeout,
                     new NodeJoinController.ElectionCallback() {
                         @Override
                         public void onElectedAsMaster(ClusterState state) {
+                            synchronized (stateMutex) {
                                 joinThreadControl.markThreadAsDone(currentThread);
-                            // we only starts nodesFD if we are master (it may be that we received a cluster state while pinging)
+                            }
-                            nodesFD.updateNodesAndPing(state); // start the nodes FD
                         }
 
                         @Override
                         public void onFailure(Throwable t) {
                             logger.trace("failed while waiting for nodes to join, rejoining", t);
+                            synchronized (stateMutex) {
                                 joinThreadControl.markThreadAsDoneAndStartNew(currentThread);
                             }
                         }
+                    }
 
             );
         } else {
@@ -418,41 +487,25 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
             // send join request
             final boolean success = joinElectedMaster(masterNode);
 
-            // finalize join through the cluster state update thread
+            synchronized (stateMutex) {
-            final DiscoveryNode finalMasterNode = masterNode;
+                if (success) {
-            clusterService.submitStateUpdateTask("finalize_join (" + masterNode + ")", new LocalClusterUpdateTask() {
+                    DiscoveryNode currentMasterNode = this.clusterState().getNodes().getMasterNode();
-                @Override
+                    if (currentMasterNode == null) {
-                public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
-                    if (!success) {
-                        // failed to join. Try again...
-                        joinThreadControl.markThreadAsDoneAndStartNew(currentThread);
-                        return unchanged();
-                    }
-
-                    if (currentState.getNodes().getMasterNode() == null) {
                         // Post 1.3.0, the master should publish a new cluster state before acking our join request. we now should have
                         // a valid master.
                         logger.debug("no master node is set, despite of join request completing. retrying pings.");
                         joinThreadControl.markThreadAsDoneAndStartNew(currentThread);
-                        return unchanged();
+                    } else if (currentMasterNode.equals(masterNode) == false) {
+                        // update cluster state
+                        joinThreadControl.stopRunningThreadAndRejoin("master_switched_while_finalizing_join");
                     }
 
-                    if (!currentState.getNodes().getMasterNode().equals(finalMasterNode)) {
-                        return joinThreadControl.stopRunningThreadAndRejoin(currentState, "master_switched_while_finalizing_join");
-                    }
-
-                    // Note: we do not have to start master fault detection here because it's set at {@link #processNextPendingClusterState }
-                    // when the first cluster state arrives.
                     joinThreadControl.markThreadAsDone(currentThread);
-                    return unchanged();
+                } else {
-                }
+                    // failed to join. Try again...
-
-                @Override
-                public void onFailure(String source, @Nullable Exception e) {
-                    logger.error("unexpected error while trying to finalize cluster join", e);
                     joinThreadControl.markThreadAsDoneAndStartNew(currentThread);
                 }
-            });
+            }
         }
     }
 
@@ -473,7 +526,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         while (true) {
             try {
                 logger.trace("joining master {}", masterNode);
-                membership.sendJoinRequestBlocking(masterNode, clusterService.localNode(), joinTimeout);
+                membership.sendJoinRequestBlocking(masterNode, transportService.getLocalNode(), joinTimeout);
                 return true;
             } catch (Exception e) {
                 final Throwable unwrap = ExceptionsHelper.unwrapCause(e);
@@ -503,18 +556,16 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
     }
 
     private void submitRejoin(String source) {
-        clusterService.submitStateUpdateTask(source, new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+        synchronized (stateMutex) {
-            @Override
+            rejoin(source);
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) {
+        }
-                return rejoin(currentState, source);
     }
 
-            @Override
+    // visible for testing
-            public void onFailure(String source, Exception e) {
+    void setState(ClusterState clusterState) {
-                logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure during [{}]", source), e);
+        synchronized (stateMutex) {
+            state.set(clusterState);
         }
-
-        });
     }
 
     // visible for testing
@@ -611,7 +662,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
     }
 
     private void removeNode(final DiscoveryNode node, final String source, final String reason) {
-        clusterService.submitStateUpdateTask(
+        masterService.submitStateUpdateTask(
                 source + "(" + node + "), reason(" + reason + ")",
                 new NodeRemovalClusterStateTaskExecutor.Task(node, reason),
                 ClusterStateTaskConfig.build(Priority.IMMEDIATE),
@@ -654,32 +705,12 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
             // We only set the new value. If the master doesn't see enough nodes it will revoke it's mastership.
             return;
         }
-        clusterService.submitStateUpdateTask("zen-disco-min-master-nodes-changed", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+        synchronized (stateMutex) {
-            @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) {
             // check if we have enough master nodes, if not, we need to move into joining the cluster again
-                if (!electMaster.hasEnoughMasterNodes(currentState.nodes())) {
+            if (!electMaster.hasEnoughMasterNodes(state.get().nodes())) {
-                    return rejoin(currentState, "not enough master nodes on change of minimum_master_nodes from [" + prevMinimumMasterNode + "] to [" + minimumMasterNodes + "]");
+                rejoin("not enough master nodes on change of minimum_master_nodes from [" + prevMinimumMasterNode + "] to [" + minimumMasterNodes + "]");
             }
-                return unchanged();
         }
-
-
-            @Override
-            public void onNoLongerMaster(String source) {
-                // ignoring (already logged)
-            }
-
-            @Override
-            public void onFailure(String source, Exception e) {
-                logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure during [{}]", source), e);
-            }
-
-            @Override
-            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                electMaster.logMinimumMasterNodesWarningIfNecessary(oldState, newState);
-            }
-        });
     }
 
     private void handleMasterGone(final DiscoveryNode masterNode, final Throwable cause, final String reason) {
@@ -694,59 +725,71 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
 
         logger.info((Supplier<?>) () -> new ParameterizedMessage("master_left [{}], reason [{}]", masterNode, reason), cause);
 
-        clusterService.submitStateUpdateTask("master_failed (" + masterNode + ")", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+        synchronized (stateMutex) {
-
+            if (localNodeMaster() == false && masterNode.equals(state.get().nodes().getMasterNode())) {
-            @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) {
-                if (!masterNode.equals(currentState.nodes().getMasterNode())) {
-                    // master got switched on us, no need to send anything
-                    return unchanged();
-                }
-
                 // flush any pending cluster states from old master, so it will not be set as master again
                 publishClusterState.pendingStatesQueue().failAllStatesAndClear(new ElasticsearchException("master left [{}]", reason));
-
+                rejoin("master left (reason = " + reason + ")");
-                return rejoin(currentState, "master left (reason = " + reason + ")");
+            }
+        }
     }
 
-            @Override
+    // return true if state has been sent to applier
-            public void onFailure(String source, Exception e) {
+    boolean processNextCommittedClusterState(String reason) {
-                logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure during [{}]", source), e);
+        assert Thread.holdsLock(stateMutex);
-            }
-
-        });
-    }
-
-    void processNextPendingClusterState(String reason) {
-        clusterService.submitStateUpdateTask("zen-disco-receive(from master [" + reason + "])", new LocalClusterUpdateTask(Priority.URGENT) {
-            ClusterState newClusterState = null;
-
-            @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) {
-                newClusterState = publishClusterState.pendingStatesQueue().getNextClusterStateToProcess();
 
+        final ClusterState newClusterState = publishClusterState.pendingStatesQueue().getNextClusterStateToProcess();
+        final ClusterState currentState = state.get();
+        final ClusterState adaptedNewClusterState;
         // all pending states have been processed
         if (newClusterState == null) {
-                    return unchanged();
+            return false;
         }
 
         assert newClusterState.nodes().getMasterNode() != null : "received a cluster state without a master";
         assert !newClusterState.blocks().hasGlobalBlock(discoverySettings.getNoMasterBlock()) : "received a cluster state with a master block";
 
-                if (currentState.nodes().isLocalNodeElectedMaster()) {
+        if (currentState.nodes().isLocalNodeElectedMaster() && newClusterState.nodes().isLocalNodeElectedMaster() == false) {
-                    return handleAnotherMaster(currentState, newClusterState.nodes().getMasterNode(), newClusterState.version(), "via a new cluster state");
+            handleAnotherMaster(currentState, newClusterState.nodes().getMasterNode(), newClusterState.version(), "via a new cluster state");
+            return false;
         }
 
+        try {
             if (shouldIgnoreOrRejectNewClusterState(logger, currentState, newClusterState)) {
-                    return unchanged();
+                String message = String.format(
+                    Locale.ROOT,
+                    "rejecting cluster state version [%d] uuid [%s] received from [%s]",
+                    newClusterState.version(),
+                    newClusterState.stateUUID(),
+                    newClusterState.nodes().getMasterNodeId()
+                );
+                throw new IllegalStateException(message);
             }
+        } catch (Exception e) {
+            try {
+                publishClusterState.pendingStatesQueue().markAsFailed(newClusterState, e);
+            } catch (Exception inner) {
+                inner.addSuppressed(e);
+                logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected exception while failing [{}]", reason), inner);
+            }
+            return false;
+        }
+
+        if (newClusterState.nodes().isLocalNodeElectedMaster()) {
+            // update the set of nodes to ping
+            nodesFD.updateNodesAndPing(newClusterState);
+        } else {
+            // check to see that we monitor the correct master of the cluster
+            if (masterFD.masterNode() == null || !masterFD.masterNode().equals(newClusterState.nodes().getMasterNode())) {
+                masterFD.restart(newClusterState.nodes().getMasterNode(), "new cluster state received and we are monitoring the wrong master [" + masterFD.masterNode() + "]");
+            }
+        }
+
         if (currentState.blocks().hasGlobalBlock(discoverySettings.getNoMasterBlock())) {
             // its a fresh update from the master as we transition from a start of not having a master to having one
             logger.debug("got first state from fresh master [{}]", newClusterState.nodes().getMasterNodeId());
-                    return newState(newClusterState);
+            adaptedNewClusterState = newClusterState;
-                }
+        } else if (newClusterState.nodes().isLocalNodeElectedMaster() == false) {
-
-
             // some optimizations to make sure we keep old objects where possible
             ClusterState.Builder builder = ClusterState.builder(newClusterState);
 
@@ -773,37 +816,44 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
                 builder.metaData(metaDataBuilder);
             }
 
-                return newState(builder.build());
+            adaptedNewClusterState = builder.build();
+        } else {
+            adaptedNewClusterState = newClusterState;
         }
 
-            @Override
+        if (currentState == adaptedNewClusterState) {
-            public void onFailure(String source, Exception e) {
+            return false;
-                logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure during [{}]", source), e);
-                if (newClusterState != null) {
-                    try {
-                        publishClusterState.pendingStatesQueue().markAsFailed(newClusterState, e);
-                    } catch (Exception inner) {
-                        inner.addSuppressed(e);
-                        logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected exception while failing [{}]", source), inner);
-                    }
-                }
         }
 
+        state.set(adaptedNewClusterState);
+
+        clusterApplier.onNewClusterState("apply cluster state (from master [" + reason + "])",
+            this::clusterState,
+            new ClusterStateTaskListener() {
                 @Override
                 public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
                     try {
-                    if (newClusterState != null) {
-                        // check to see that we monitor the correct master of the cluster
-                        if (masterFD.masterNode() == null || !masterFD.masterNode().equals(newClusterState.nodes().getMasterNode())) {
-                            masterFD.restart(newClusterState.nodes().getMasterNode(), "new cluster state received and we are monitoring the wrong master [" + masterFD.masterNode() + "]");
-                        }
                         publishClusterState.pendingStatesQueue().markAsProcessed(newClusterState);
-                    }
                     } catch (Exception e) {
                         onFailure(source, e);
                     }
                 }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure applying [{}]", reason), e);
+                    try {
+                        // TODO: use cluster state uuid instead of full cluster state so that we don't keep reference to CS around
+                        // for too long.
+                        publishClusterState.pendingStatesQueue().markAsFailed(newClusterState, e);
+                    } catch (Exception inner) {
+                        inner.addSuppressed(e);
+                        logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected exception while failing [{}]", reason), inner);
+                    }
+                }
             });
+
+        return true;
     }
 
     /**
@@ -888,13 +938,13 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
             logger.trace("full ping responses:{}", sb);
         }
 
-        final DiscoveryNode localNode = clusterService.localNode();
+        final DiscoveryNode localNode = transportService.getLocalNode();
 
         // add our selves
         assert fullPingResponses.stream().map(ZenPing.PingResponse::node)
             .filter(n -> n.equals(localNode)).findAny().isPresent() == false;
 
-        fullPingResponses.add(new ZenPing.PingResponse(localNode, null, clusterService.state()));
+        fullPingResponses.add(new ZenPing.PingResponse(localNode, null, this.clusterState()));
 
         // filter responses
         final List<ZenPing.PingResponse> pingResponses = filterPingResponses(fullPingResponses, masterElectionIgnoreNonMasters, logger);
@@ -956,10 +1006,9 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         return pingResponses;
     }
 
-    protected ClusterStateTaskExecutor.ClusterTasksResult<LocalClusterUpdateTask> rejoin(ClusterState clusterState, String reason) {
+    protected void rejoin(String reason) {
-
+        assert Thread.holdsLock(stateMutex);
-        // *** called from within an cluster state update task *** //
+        ClusterState clusterState = state.get();
-        assert Thread.currentThread().getName().contains(ClusterService.UPDATE_THREAD_NAME);
 
         logger.warn("{}, current nodes: {}", reason, clusterState.nodes());
         nodesFD.stop();
@@ -968,44 +1017,54 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         // TODO: do we want to force a new thread if we actively removed the master? this is to give a full pinging cycle
         // before a decision is made.
         joinThreadControl.startNewThreadIfNotRunning();
-        return LocalClusterUpdateTask.noMaster();
+
+        if (clusterState.nodes().getMasterNodeId() != null) {
+            // remove block if it already exists before adding new one
+            assert clusterState.blocks().hasGlobalBlock(discoverySettings.getNoMasterBlock().id()) == false :
+                "NO_MASTER_BLOCK should only be added by ZenDiscovery";
+            ClusterBlocks clusterBlocks = ClusterBlocks.builder().blocks(clusterState.blocks())
+                .addGlobalBlock(discoverySettings.getNoMasterBlock())
+                .build();
+
+            DiscoveryNodes discoveryNodes = new DiscoveryNodes.Builder(clusterState.nodes()).masterNodeId(null).build();
+            clusterState = ClusterState.builder(clusterState)
+                .blocks(clusterBlocks)
+                .nodes(discoveryNodes)
+                .build();
+
+            state.set(clusterState);
+            clusterApplier.onNewClusterState(reason, this::clusterState, (source, e) -> {}); // don't wait for state to be applied
+        }
     }
 
     private boolean localNodeMaster() {
         return nodes().isLocalNodeElectedMaster();
     }
 
-    private ClusterStateTaskExecutor.ClusterTasksResult handleAnotherMaster(ClusterState localClusterState, final DiscoveryNode otherMaster, long otherClusterStateVersion, String reason) {
+    private void handleAnotherMaster(ClusterState localClusterState, final DiscoveryNode otherMaster, long otherClusterStateVersion, String reason) {
         assert localClusterState.nodes().isLocalNodeElectedMaster() : "handleAnotherMaster called but current node is not a master";
-        assert Thread.currentThread().getName().contains(ClusterService.UPDATE_THREAD_NAME) : "not called from the cluster state update thread";
+        assert Thread.holdsLock(stateMutex);
 
         if (otherClusterStateVersion > localClusterState.version()) {
-            return rejoin(localClusterState, "zen-disco-discovered another master with a new cluster_state [" + otherMaster + "][" + reason + "]");
+            rejoin("zen-disco-discovered another master with a new cluster_state [" + otherMaster + "][" + reason + "]");
         } else {
+            // TODO: do this outside mutex
             logger.warn("discovered [{}] which is also master but with an older cluster_state, telling [{}] to rejoin the cluster ([{}])", otherMaster, otherMaster, reason);
-            // spawn to a background thread to not do blocking operations on the cluster state thread
+            try {
-            threadPool.generic().execute(new AbstractRunnable() {
-                @Override
-                public void onFailure(Exception e) {
-                    logger.warn((Supplier<?>) () -> new ParameterizedMessage("failed to send rejoin request to [{}]", otherMaster), e);
-                }
-
-                @Override
-                protected void doRun() throws Exception {
                 // make sure we're connected to this node (connect to node does nothing if we're already connected)
                 // since the network connections are asymmetric, it may be that we received a state but have disconnected from the node
                 // in the past (after a master failure, for example)
                 transportService.connectToNode(otherMaster);
-                    transportService.sendRequest(otherMaster, DISCOVERY_REJOIN_ACTION_NAME, new RejoinClusterRequest(localNode().getId()), new EmptyTransportResponseHandler(ThreadPool.Names.SAME) {
+                transportService.sendRequest(otherMaster, DISCOVERY_REJOIN_ACTION_NAME, new RejoinClusterRequest(localClusterState.nodes().getLocalNodeId()), new EmptyTransportResponseHandler(ThreadPool.Names.SAME) {
 
                     @Override
                     public void handleException(TransportException exp) {
                         logger.warn((Supplier<?>) () -> new ParameterizedMessage("failed to send rejoin request to [{}]", otherMaster), exp);
                     }
                 });
+            } catch (Exception e) {
+                logger.warn((Supplier<?>) () -> new ParameterizedMessage("failed to send rejoin request to [{}]", otherMaster), e);
             }
-            });
-            return LocalClusterUpdateTask.unchanged();
         }
     }
 
@@ -1033,14 +1092,16 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
 
         @Override
         public void onNewClusterState(String reason) {
-            processNextPendingClusterState(reason);
+            synchronized (stateMutex) {
+                processNextCommittedClusterState(reason);
+            }
         }
     }
 
     private class MembershipListener implements MembershipAction.MembershipListener {
         @Override
         public void onJoin(DiscoveryNode node, MembershipAction.JoinCallback callback) {
-            handleJoinRequest(node, clusterService.state(), callback);
+            handleJoinRequest(node, ZenDiscovery.this.clusterState(), callback);
         }
 
         @Override
@@ -1072,23 +1133,13 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
                 return;
             }
             logger.debug("got a ping from another master {}. resolving who should rejoin. current ping count: [{}]", pingRequest.masterNode(), pingsWhileMaster.get());
-            clusterService.submitStateUpdateTask("ping from another master", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+            synchronized (stateMutex) {
-
+                ClusterState currentState = state.get();
-                @Override
-                public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
                 if (currentState.nodes().isLocalNodeElectedMaster()) {
                     pingsWhileMaster.set(0);
-                        return handleAnotherMaster(currentState, pingRequest.masterNode(), pingRequest.clusterStateVersion(), "node fd ping");
+                    handleAnotherMaster(currentState, pingRequest.masterNode(), pingRequest.clusterStateVersion(), "node fd ping");
-                    } else {
-                        return unchanged();
                 }
             }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    logger.debug("unexpected error during cluster state update task after pings from another master", e);
-                }
-            });
         }
     }
 
@@ -1127,23 +1178,14 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
     class RejoinClusterRequestHandler implements TransportRequestHandler<RejoinClusterRequest> {
         @Override
         public void messageReceived(final RejoinClusterRequest request, final TransportChannel channel) throws Exception {
-            clusterService.submitStateUpdateTask("received a request to rejoin the cluster from [" + request.fromNodeId + "]", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
-
-                @Override
-                public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) {
             try {
                 channel.sendResponse(TransportResponse.Empty.INSTANCE);
             } catch (Exception e) {
                 logger.warn("failed to send response on rejoin cluster request handling", e);
             }
-                    return rejoin(currentState, "received a request to rejoin the cluster from [" + request.fromNodeId + "]");
+            synchronized (stateMutex) {
+                rejoin("received a request to rejoin the cluster from [" + request.fromNodeId + "]");
             }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    logger.error((Supplier<?>) () -> new ParameterizedMessage("unexpected failure during [{}]", source), e);
-                }
-            });
         }
     }
 
@@ -1169,15 +1211,15 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         }
 
         /** cleans any running joining thread and calls {@link #rejoin} */
-        public ClusterStateTaskExecutor.ClusterTasksResult<LocalClusterUpdateTask> stopRunningThreadAndRejoin(ClusterState clusterState, String reason) {
+        public void stopRunningThreadAndRejoin(String reason) {
-            ClusterService.assertClusterStateThread();
+            assert Thread.holdsLock(stateMutex);
             currentJoinThread.set(null);
-            return rejoin(clusterState, reason);
+            rejoin(reason);
         }
 
         /** starts a new joining thread if there is no currently active one and join thread controlling is started */
         public void startNewThreadIfNotRunning() {
-            ClusterService.assertClusterStateThread();
+            assert Thread.holdsLock(stateMutex);
             if (joinThreadActive()) {
                 return;
             }
@@ -1210,7 +1252,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
          * If the given thread is not the currently running join thread, the command is ignored.
          */
         public void markThreadAsDoneAndStartNew(Thread joinThread) {
-            ClusterService.assertClusterStateThread();
+            assert Thread.holdsLock(stateMutex);
             if (!markThreadAsDone(joinThread)) {
                 return;
             }
@@ -1219,7 +1261,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
 
         /** marks the given joinThread as completed. Returns false if the supplied thread is not the currently active join thread */
         public boolean markThreadAsDone(Thread joinThread) {
-            ClusterService.assertClusterStateThread();
+            assert Thread.holdsLock(stateMutex);
             return currentJoinThread.compareAndSet(joinThread, null);
         }
 

core/src/main/java/org/elasticsearch/gateway/GatewayService.java

@@ -122,9 +122,6 @@ public class GatewayService extends AbstractLifecycleComponent implements Cluste
             // TODO: change me once the minimum_master_nodes is changed too
             recoverAfterMasterNodes = settings.getAsInt("discovery.zen.minimum_master_nodes", -1);
         }
-
-        // Add the not recovered as initial state block, we don't allow anything until
-        this.clusterService.addInitialStateBlock(STATE_NOT_RECOVERED_BLOCK);
     }
 
     @Override

core/src/main/java/org/elasticsearch/indices/store/IndicesStore.java

@@ -26,7 +26,6 @@ import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateListener;
 import org.elasticsearch.cluster.ClusterStateObserver;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.IndexRoutingTable;
@@ -280,26 +279,20 @@ public class IndicesStore extends AbstractComponent implements ClusterStateListe
                 return;
             }
 
-            clusterService.submitStateUpdateTask("indices_store ([" + shardId + "] active fully on other nodes)", new LocalClusterUpdateTask() {
+            clusterService.getClusterApplierService().runOnApplierThread("indices_store ([" + shardId + "] active fully on other nodes)",
-                @Override
+                currentState -> {
-                public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
                     if (clusterStateVersion != currentState.getVersion()) {
                         logger.trace("not deleting shard {}, the update task state version[{}] is not equal to cluster state before shard active api call [{}]", shardId, currentState.getVersion(), clusterStateVersion);
-                        return unchanged();
+                        return;
                     }
                     try {
                         indicesService.deleteShardStore("no longer used", shardId, currentState);
                     } catch (Exception ex) {
                         logger.debug((Supplier<?>) () -> new ParameterizedMessage("{} failed to delete unallocated shard, ignoring", shardId), ex);
                     }
-                    return unchanged();
+                },
-                }
+                (source, e) -> logger.error((Supplier<?>) () -> new ParameterizedMessage("{} unexpected error during deletion of unallocated shard", shardId), e)
-
+            );
-                @Override
-                public void onFailure(String source, Exception e) {
-                    logger.error((Supplier<?>) () -> new ParameterizedMessage("{} unexpected error during deletion of unallocated shard", shardId), e);
-                }
-            });
         }
 
     }

core/src/main/java/org/elasticsearch/node/Node.java

@@ -260,7 +260,7 @@ public class Node implements Closeable {
                 nodeEnvironment = new NodeEnvironment(tmpSettings, environment);
                 resourcesToClose.add(nodeEnvironment);
             } catch (IOException ex) {
-                throw new IllegalStateException("Failed to created node environment", ex);
+                throw new IllegalStateException("Failed to create node environment", ex);
             }
             final boolean hadPredefinedNodeName = NODE_NAME_SETTING.exists(tmpSettings);
             Logger logger = Loggers.getLogger(Node.class, tmpSettings);
@@ -336,8 +336,7 @@ public class Node implements Closeable {
             resourcesToClose.add(resourceWatcherService);
             final NetworkService networkService = new NetworkService(settings,
                 getCustomNameResolvers(pluginsService.filterPlugins(DiscoveryPlugin.class)));
-            final ClusterService clusterService = new ClusterService(settings, settingsModule.getClusterSettings(), threadPool,
+            final ClusterService clusterService = new ClusterService(settings, settingsModule.getClusterSettings(), threadPool);
-                localNodeFactory::getNode);
             clusterService.addListener(scriptModule.getScriptService());
             resourcesToClose.add(clusterService);
             final IngestService ingestService = new IngestService(settings, threadPool, this.environment,
@@ -428,12 +427,13 @@ public class Node implements Closeable {
                 };
                 httpServerTransport = null;
             }
-            final DiscoveryModule discoveryModule = new DiscoveryModule(this.settings, threadPool, transportService,
+
-                namedWriteableRegistry, networkService, clusterService, pluginsService.filterPlugins(DiscoveryPlugin.class));
+            final DiscoveryModule discoveryModule = new DiscoveryModule(this.settings, threadPool, transportService, namedWriteableRegistry,
+                networkService, clusterService.getMasterService(), clusterService.getClusterApplierService(),
+                clusterService.getClusterSettings(), pluginsService.filterPlugins(DiscoveryPlugin.class));
             NodeService nodeService = new NodeService(settings, threadPool, monitorService, discoveryModule.getDiscovery(),
                 transportService, indicesService, pluginsService, circuitBreakerService, scriptModule.getScriptService(),
                 httpServerTransport, ingestService, clusterService, settingsModule.getSettingsFilter());
-
             modules.add(b -> {
                     b.bind(NodeService.class).toInstance(nodeService);
                     b.bind(NamedXContentRegistry.class).toInstance(xContentRegistry);
@@ -662,9 +662,7 @@ public class Node implements Closeable {
         injector.getInstance(ResourceWatcherService.class).start();
         injector.getInstance(GatewayService.class).start();
         Discovery discovery = injector.getInstance(Discovery.class);
-        clusterService.setDiscoverySettings(discovery.getDiscoverySettings());
+        clusterService.getMasterService().setClusterStatePublisher(discovery::publish);
-        clusterService.addInitialStateBlock(discovery.getDiscoverySettings().getNoMasterBlock());
-        clusterService.setClusterStatePublisher(discovery::publish);
 
         // start before the cluster service since it adds/removes initial Cluster state blocks
         final TribeService tribeService = injector.getInstance(TribeService.class);
@@ -674,18 +672,20 @@ public class Node implements Closeable {
         TransportService transportService = injector.getInstance(TransportService.class);
         transportService.getTaskManager().setTaskResultsService(injector.getInstance(TaskResultsService.class));
         transportService.start();
+        assert localNodeFactory.getNode() != null;
+        assert transportService.getLocalNode().equals(localNodeFactory.getNode())
+            : "transportService has a different local node than the factory provided";
         validateNodeBeforeAcceptingRequests(settings, transportService.boundAddress(), pluginsService.filterPlugins(Plugin.class).stream()
             .flatMap(p -> p.getBootstrapChecks().stream()).collect(Collectors.toList()));
 
         clusterService.addStateApplier(transportService.getTaskManager());
+        clusterService.getMasterService().setClusterStateSupplier(discovery::clusterState);
+        clusterService.getClusterApplierService().setInitialState(discovery.getInitialClusterState());
+        // start after transport service so the local disco is known
         clusterService.start();
-        assert localNodeFactory.getNode() != null;
+        discovery.start();
-        assert transportService.getLocalNode().equals(localNodeFactory.getNode())
-            : "transportService has a different local node than the factory provided";
         assert clusterService.localNode().equals(localNodeFactory.getNode())
             : "clusterService has a different local node than the factory provided";
-        // start after cluster service so the local disco is known
-        discovery.start();
         transportService.acceptIncomingRequests();
         discovery.startInitialJoin();
         // tribe nodes don't have a master so we shouldn't register an observer         s

core/src/main/java/org/elasticsearch/node/NodeService.java

@@ -82,7 +82,7 @@ public class NodeService extends AbstractComponent implements Closeable {
 
     public NodeInfo info(boolean settings, boolean os, boolean process, boolean jvm, boolean threadPool,
                 boolean transport, boolean http, boolean plugin, boolean ingest, boolean indices) {
-        return new NodeInfo(Version.CURRENT, Build.CURRENT, discovery.localNode(),
+        return new NodeInfo(Version.CURRENT, Build.CURRENT, transportService.getLocalNode(),
                 settings ? settingsFilter.filter(this.settings) : null,
                 os ? monitorService.osService().info() : null,
                 process ? monitorService.processService().info() : null,
@@ -101,7 +101,7 @@ public class NodeService extends AbstractComponent implements Closeable {
                            boolean script, boolean discoveryStats, boolean ingest) {
         // for indices stats we want to include previous allocated shards stats as well (it will
         // only be applied to the sensible ones to use, like refresh/merge/flush/indexing stats)
-        return new NodeStats(discovery.localNode(), System.currentTimeMillis(),
+        return new NodeStats(transportService.getLocalNode(), System.currentTimeMillis(),
                 indices.anySet() ? indicesService.stats(true, indices) : null,
                 os ? monitorService.osService().stats() : null,
                 process ? monitorService.processService().stats() : null,

core/src/main/java/org/elasticsearch/plugins/DiscoveryPlugin.java

@@ -23,13 +23,14 @@ import java.util.Collections;
 import java.util.Map;
 import java.util.function.Supplier;
 
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.zen.UnicastHostsProvider;
-import org.elasticsearch.discovery.zen.ZenPing;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 
@@ -57,12 +58,17 @@ public interface DiscoveryPlugin {
      *
      * @param threadPool Use to schedule ping actions
      * @param transportService Use to communicate with other nodes
-     * @param clusterService Use to find current nodes in the cluster
+     * @param masterService Use to submit cluster state update tasks
+     * @param clusterApplier Use to locally apply cluster state updates
+     * @param clusterSettings Use to get cluster settings
      * @param hostsProvider Use to find configured hosts which should be pinged for initial discovery
      */
     default Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                                NamedWriteableRegistry namedWriteableRegistry,
-                                                               ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                               MasterService masterService,
+                                                               ClusterApplier clusterApplier,
+                                                               ClusterSettings clusterSettings,
+                                                               UnicastHostsProvider hostsProvider) {
         return Collections.emptyMap();
     }
 

core/src/main/java/org/elasticsearch/repositories/RepositoriesService.java

@@ -148,7 +148,8 @@ public class RepositoriesService extends AbstractComponent implements ClusterSta
 
             @Override
             public boolean mustAck(DiscoveryNode discoveryNode) {
-                return discoveryNode.isMasterNode();
+                // repository is created on both master and data nodes
+                return discoveryNode.isMasterNode() || discoveryNode.isDataNode();
             }
         });
     }
@@ -198,8 +199,8 @@ public class RepositoriesService extends AbstractComponent implements ClusterSta
 
             @Override
             public boolean mustAck(DiscoveryNode discoveryNode) {
-                // Since operation occurs only on masters, it's enough that only master-eligible nodes acked
+                // repository was created on both master and data nodes
-                return discoveryNode.isMasterNode();
+                return discoveryNode.isMasterNode() || discoveryNode.isDataNode();
             }
         });
     }

core/src/main/java/org/elasticsearch/rest/action/cat/RestAliasAction.java

@@ -46,7 +46,7 @@ public class RestAliasAction extends AbstractCatAction {
     @Override
     protected RestChannelConsumer doCatRequest(final RestRequest request, final NodeClient client) {
         final GetAliasesRequest getAliasesRequest = request.hasParam("alias") ?
-                new GetAliasesRequest(request.param("alias")) :
+                new GetAliasesRequest(Strings.commaDelimitedListToStringArray(request.param("alias"))) :
                 new GetAliasesRequest();
         getAliasesRequest.local(request.paramAsBoolean("local", getAliasesRequest.local()));
 

core/src/main/java/org/elasticsearch/search/aggregations/metrics/geocentroid/InternalGeoCentroid.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.search.aggregations.metrics.geocentroid;
 
 import org.apache.lucene.geo.GeoEncodingUtils;
+import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.geo.GeoPoint;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -36,8 +37,8 @@ import java.util.Objects;
  * Serialization and merge logic for {@link GeoCentroidAggregator}.
  */
 public class InternalGeoCentroid extends InternalAggregation implements GeoCentroid {
-    protected final GeoPoint centroid;
+    private final GeoPoint centroid;
-    protected final long count;
+    private final long count;
 
     public static long encodeLatLon(double lat, double lon) {
         return (Integer.toUnsignedLong(GeoEncodingUtils.encodeLatitude(lat)) << 32) | Integer.toUnsignedLong(GeoEncodingUtils.encodeLongitude(lon));
@@ -136,6 +137,8 @@ public class InternalGeoCentroid extends InternalAggregation implements GeoCentr
                     return centroid.lat();
                 case "lon":
                     return centroid.lon();
+                case "count":
+                    return count;
                 default:
                     throw new IllegalArgumentException("Found unknown path element [" + coordinate + "] in [" + getName() + "]");
             }
@@ -145,14 +148,27 @@ public class InternalGeoCentroid extends InternalAggregation implements GeoCentr
     }
 
     static class Fields {
-        static final String CENTROID = "location";
+        static final ParseField CENTROID = new ParseField("location");
+        static final ParseField CENTROID_LAT = new ParseField("lat");
+        static final ParseField CENTROID_LON = new ParseField("lon");
+        static final ParseField COUNT = new ParseField("count");
     }
 
     @Override
     public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
-        if (centroid != null) {
+        return renderXContent(builder, params, centroid, count);
-            builder.startObject(Fields.CENTROID).field("lat", centroid.lat()).field("lon", centroid.lon()).endObject();
     }
+
+    static XContentBuilder renderXContent(XContentBuilder builder, Params params, GeoPoint centroid, long count) throws IOException {
+        if (centroid != null) {
+            builder.startObject(Fields.CENTROID.getPreferredName());
+            {
+                builder.field(Fields.CENTROID_LAT.getPreferredName(), centroid.lat());
+                builder.field(Fields.CENTROID_LON.getPreferredName(), centroid.lon());
+            }
+            builder.endObject();
+        }
+        builder.field(Fields.COUNT.getPreferredName(), count);
         return builder;
     }
 

core/src/main/java/org/elasticsearch/tribe/TribeService.java

@@ -43,6 +43,7 @@ import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.component.AbstractLifecycleComponent;
+import org.elasticsearch.common.component.Lifecycle;
 import org.elasticsearch.common.hash.MurmurHash3;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.NamedWriteableAwareStreamInput;
@@ -73,6 +74,7 @@ import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.function.Function;
@@ -129,7 +131,7 @@ public class TribeService extends AbstractLifecycleComponent {
         if (!NodeEnvironment.MAX_LOCAL_STORAGE_NODES_SETTING.exists(settings)) {
             sb.put(NodeEnvironment.MAX_LOCAL_STORAGE_NODES_SETTING.getKey(), nodesSettings.size());
         }
-        sb.put(DiscoveryModule.DISCOVERY_TYPE_SETTING.getKey(), "none"); // a tribe node should not use zen discovery
+        sb.put(DiscoveryModule.DISCOVERY_TYPE_SETTING.getKey(), "tribe"); // there is a special discovery implementation for tribe
         // nothing is going to be discovered, since no master will be elected
         sb.put(DiscoverySettings.INITIAL_STATE_TIMEOUT_SETTING.getKey(), 0);
         if (sb.get("cluster.name") == null) {
@@ -230,16 +232,6 @@ public class TribeService extends AbstractLifecycleComponent {
         this.blockIndicesMetadata = BLOCKS_METADATA_INDICES_SETTING.get(settings).toArray(Strings.EMPTY_ARRAY);
         this.blockIndicesRead = BLOCKS_READ_INDICES_SETTING.get(settings).toArray(Strings.EMPTY_ARRAY);
         this.blockIndicesWrite = BLOCKS_WRITE_INDICES_SETTING.get(settings).toArray(Strings.EMPTY_ARRAY);
-
-        if (!nodes.isEmpty()) {
-            if (BLOCKS_WRITE_SETTING.get(settings)) {
-                clusterService.addInitialStateBlock(TRIBE_WRITE_BLOCK);
-            }
-            if (BLOCKS_METADATA_SETTING.get(settings)) {
-                clusterService.addInitialStateBlock(TRIBE_METADATA_BLOCK);
-            }
-        }
-
         this.onConflict = ON_CONFLICT_SETTING.get(settings);
     }
 
@@ -290,12 +282,7 @@ public class TribeService extends AbstractLifecycleComponent {
 
     @Override
     protected void doStart() {
-        if (nodes.isEmpty() == false) {
+
-            // remove the initial election / recovery blocks since we are not going to have a
-            // master elected in this single tribe  node local "cluster"
-            clusterService.removeInitialStateBlock(DiscoverySettings.NO_MASTER_BLOCK_ID);
-            clusterService.removeInitialStateBlock(GatewayService.STATE_NOT_RECOVERED_BLOCK);
-        }
     }
 
     public void startNodes() {
@@ -516,7 +503,10 @@ public class TribeService extends AbstractLifecycleComponent {
             final List<Node> tribeClientNodes = TribeService.this.nodes;
             Map<String, MetaData.Custom> mergedCustomMetaDataMap = mergeChangedCustomMetaData(changedCustomMetaDataTypeSet,
                     customMetaDataType -> tribeClientNodes.stream()
-                            .map(TribeService::getClusterService).map(ClusterService::state)
+                            .map(TribeService::getClusterService)
+                            // cluster service might not have initial state yet (as tribeClientNodes are started after main node)
+                            .filter(cs -> cs.lifecycleState() == Lifecycle.State.STARTED)
+                            .map(ClusterService::state)
                             .map(ClusterState::metaData)
                             .map(clusterMetaData -> ((MetaData.Custom) clusterMetaData.custom(customMetaDataType)))
                             .filter(custom1 -> custom1 != null && custom1 instanceof MergableCustomMetaData)

core/src/test/java/org/elasticsearch/action/bulk/BulkRequestTests.java

@@ -40,6 +40,7 @@ import org.elasticsearch.test.ESTestCase;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -255,4 +256,39 @@ public class BulkRequestTests extends ESTestCase {
         assertEquals(1, request.sourceAsMap().size());
         assertEquals("value", request.sourceAsMap().get("field"));
     }
+
+    public void testToValidateUpsertRequestAndVersionInBulkRequest() throws IOException {
+        XContentType xContentType = XContentType.SMILE;
+        BytesReference data;
+        try (BytesStreamOutput out = new BytesStreamOutput()) {
+            try (XContentBuilder builder = XContentFactory.contentBuilder(xContentType, out)) {
+                builder.startObject();
+                builder.startObject("update");
+                builder.field("_index", "index");
+                builder.field("_type", "type");
+                builder.field("_id", "id");
+                builder.field("_version", 1L);
+                builder.endObject();
+                builder.endObject();
+            }
+            out.write(xContentType.xContent().streamSeparator());
+            try(XContentBuilder builder = XContentFactory.contentBuilder(xContentType, out)) {
+                builder.startObject();
+                builder.field("doc", "{}");
+                Map<String,Object> values = new HashMap<>();
+                values.put("_version", 2L);
+                values.put("_index", "index");
+                values.put("_type", "type");
+                builder.field("upsert", values);
+                builder.endObject();
+            }
+            out.write(xContentType.xContent().streamSeparator());
+            data = out.bytes();
+        }
+        BulkRequest bulkRequest = new BulkRequest();
+        bulkRequest.add(data, null, null, xContentType);
+        assertThat(bulkRequest.validate().validationErrors(), contains("can't provide both upsert request and a version",
+            "can't provide version in upsert request"));
+    }
+
 }

core/src/test/java/org/elasticsearch/action/update/UpdateRequestTests.java

@@ -59,9 +59,11 @@ import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
 import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
 import static org.elasticsearch.common.xcontent.XContentHelper.toXContent;
+import static org.elasticsearch.common.xcontent.XContentHelper.update;
 import static org.elasticsearch.script.MockScriptEngine.mockInlineScript;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertToXContentEquivalent;
 import static org.hamcrest.Matchers.arrayContaining;
+import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.notNullValue;
@@ -485,4 +487,19 @@ public class UpdateRequestTests extends ESTestCase {
         BytesReference finalBytes = toXContent(parsedUpdateRequest, xContentType, humanReadable);
         assertToXContentEquivalent(originalBytes, finalBytes, xContentType);
     }
+
+    public void testToValidateUpsertRequestAndVersion() {
+        UpdateRequest updateRequest = new UpdateRequest("index", "type", "id");
+        updateRequest.version(1L);
+        updateRequest.doc("{}", XContentType.JSON);
+        updateRequest.upsert(new IndexRequest("index","type", "id"));
+        assertThat(updateRequest.validate().validationErrors(), contains("can't provide both upsert request and a version"));
+    }
+
+    public void testToValidateUpsertRequestWithVersion() {
+        UpdateRequest updateRequest = new UpdateRequest("index", "type", "id");
+        updateRequest.doc("{}", XContentType.JSON);
+        updateRequest.upsert(new IndexRequest("index", "type", "1").version(1L));
+        assertThat(updateRequest.validate().validationErrors(), contains("can't provide version in upsert request"));
+    }
 }

core/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java

@@ -19,8 +19,6 @@
 
 package org.elasticsearch.cluster;
 
-import org.elasticsearch.Version;
-import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
 import org.elasticsearch.cluster.routing.allocation.ShardAllocationDecision;
@@ -41,7 +39,6 @@ import org.elasticsearch.cluster.routing.allocation.decider.ShardsLimitAllocatio
 import org.elasticsearch.cluster.routing.allocation.decider.SnapshotInProgressAllocationDecider;
 import org.elasticsearch.cluster.routing.allocation.decider.ThrottlingAllocationDecider;
 import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.inject.ModuleTestCase;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.IndexScopedSettings;
@@ -61,8 +58,7 @@ import java.util.function.Supplier;
 
 public class ClusterModuleTests extends ModuleTestCase {
     private ClusterService clusterService = new ClusterService(Settings.EMPTY,
-        new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS), null, () ->
+        new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS), null);
-        new DiscoveryNode(UUIDs.randomBase64UUID(), buildNewFakeTransportAddress(), Version.CURRENT));
     static class FakeAllocationDecider extends AllocationDecider {
         protected FakeAllocationDecider(Settings settings) {
             super(settings);

core/src/test/java/org/elasticsearch/cluster/health/ClusterStateHealthTests.java

@@ -29,7 +29,6 @@ import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.action.support.PlainActionFuture;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.metadata.MetaData;
@@ -130,18 +129,11 @@ public class ClusterStateHealthTests extends ESTestCase {
         });
 
         logger.info("--> submit task to restore master");
-        clusterService.submitStateUpdateTask("restore master", new LocalClusterUpdateTask() {
+        ClusterState currentState = clusterService.getClusterApplierService().state();
-            @Override
+        clusterService.getClusterApplierService().onNewClusterState("restore master",
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
+            () -> ClusterState.builder(currentState)
-                return newState(ClusterState.builder(currentState).nodes(
+                .nodes(DiscoveryNodes.builder(currentState.nodes()).masterNodeId(currentState.nodes().getLocalNodeId())).build(),
-                    DiscoveryNodes.builder(currentState.nodes()).masterNodeId(currentState.nodes().getLocalNodeId())).build());
+            (source, e) -> {});
-            }
-
-            @Override
-            public void onFailure(String source, Exception e) {
-                logger.warn("unexpected failure", e);
-            }
-        });
 
         logger.info("--> waiting for listener to be called and cluster state being blocked");
         listenerCalled.await();

core/src/test/java/org/elasticsearch/cluster/routing/DelayedAllocationServiceTests.java

@@ -470,7 +470,7 @@ public class DelayedAllocationServiceTests extends ESAllocationTestCase {
         }
 
         @Override
-        protected void assertClusterStateThread() {
+        protected void assertClusterOrMasterStateThread() {
             // do not check this in the unit tests
         }
 

core/src/test/java/org/elasticsearch/cluster/service/ClusterApplierServiceTests.java

@@ -0,0 +1,427 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.cluster.service;
+
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.Version;
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.cluster.ClusterName;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateObserver;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
+import org.elasticsearch.cluster.LocalNodeMasterListener;
+import org.elasticsearch.cluster.NodeConnectionsService;
+import org.elasticsearch.cluster.block.ClusterBlocks;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.ClusterSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.discovery.DiscoverySettings;
+import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.MockLogAppender;
+import org.elasticsearch.test.junit.annotations.TestLogging;
+import org.elasticsearch.threadpool.TestThreadPool;
+import org.elasticsearch.threadpool.ThreadPool;
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.emptySet;
+import static org.elasticsearch.test.ClusterServiceUtils.setState;
+import static org.hamcrest.Matchers.is;
+
+public class ClusterApplierServiceTests extends ESTestCase {
+
+    protected static ThreadPool threadPool;
+    protected TimedClusterApplierService clusterApplierService;
+
+    @BeforeClass
+    public static void createThreadPool() {
+        threadPool = new TestThreadPool(ClusterApplierServiceTests.class.getName());
+    }
+
+    @AfterClass
+    public static void stopThreadPool() {
+        if (threadPool != null) {
+            threadPool.shutdownNow();
+            threadPool = null;
+        }
+    }
+
+    @Before
+    public void setUp() throws Exception {
+        super.setUp();
+        clusterApplierService = createTimedClusterService(true);
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        clusterApplierService.close();
+        super.tearDown();
+    }
+
+    TimedClusterApplierService createTimedClusterService(boolean makeMaster) throws InterruptedException {
+        DiscoveryNode localNode = new DiscoveryNode("node1", buildNewFakeTransportAddress(), emptyMap(),
+            emptySet(), Version.CURRENT);
+        TimedClusterApplierService timedClusterApplierService = new TimedClusterApplierService(Settings.builder().put("cluster.name",
+            "ClusterApplierServiceTests").build(), new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
+            threadPool);
+        timedClusterApplierService.setNodeConnectionsService(new NodeConnectionsService(Settings.EMPTY, null, null) {
+            @Override
+            public void connectToNodes(DiscoveryNodes discoveryNodes) {
+                // skip
+            }
+
+            @Override
+            public void disconnectFromNodesExcept(DiscoveryNodes nodesToKeep) {
+                // skip
+            }
+        });
+        timedClusterApplierService.setInitialState(ClusterState.builder(new ClusterName("ClusterApplierServiceTests"))
+            .nodes(DiscoveryNodes.builder()
+                .add(localNode)
+                .localNodeId(localNode.getId())
+                .masterNodeId(makeMaster ? localNode.getId() : null))
+            .blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).build());
+        timedClusterApplierService.start();
+        return timedClusterApplierService;
+    }
+
+    @TestLogging("org.elasticsearch.cluster.service:TRACE") // To ensure that we log cluster state events on TRACE level
+    public void testClusterStateUpdateLogging() throws Exception {
+        MockLogAppender mockAppender = new MockLogAppender();
+        mockAppender.start();
+        mockAppender.addExpectation(
+                new MockLogAppender.SeenEventExpectation(
+                        "test1",
+                        clusterApplierService.getClass().getName(),
+                        Level.DEBUG,
+                        "*processing [test1]: took [1s] no change in cluster state"));
+        mockAppender.addExpectation(
+                new MockLogAppender.SeenEventExpectation(
+                        "test2",
+                        clusterApplierService.getClass().getName(),
+                        Level.TRACE,
+                        "*failed to execute cluster state applier in [2s]*"));
+
+        Logger clusterLogger = Loggers.getLogger("org.elasticsearch.cluster.service");
+        Loggers.addAppender(clusterLogger, mockAppender);
+        try {
+            final CountDownLatch latch = new CountDownLatch(3);
+            clusterApplierService.currentTimeOverride = System.nanoTime();
+            clusterApplierService.runOnApplierThread("test1",
+                currentState -> clusterApplierService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos(),
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        fail();
+                    }
+            });
+            clusterApplierService.runOnApplierThread("test2",
+                currentState -> {
+                    clusterApplierService.currentTimeOverride += TimeValue.timeValueSeconds(2).nanos();
+                    throw new IllegalArgumentException("Testing handling of exceptions in the cluster state task");
+                },
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        fail();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        latch.countDown();
+                    }
+                });
+            // Additional update task to make sure all previous logging made it to the loggerName
+            // We don't check logging for this on since there is no guarantee that it will occur before our check
+            clusterApplierService.runOnApplierThread("test3",
+                currentState -> {},
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        fail();
+                    }
+                });
+            latch.await();
+        } finally {
+            Loggers.removeAppender(clusterLogger, mockAppender);
+            mockAppender.stop();
+        }
+        mockAppender.assertAllExpectationsMatched();
+    }
+
+    @TestLogging("org.elasticsearch.cluster.service:WARN") // To ensure that we log cluster state events on WARN level
+    public void testLongClusterStateUpdateLogging() throws Exception {
+        MockLogAppender mockAppender = new MockLogAppender();
+        mockAppender.start();
+        mockAppender.addExpectation(
+                new MockLogAppender.UnseenEventExpectation(
+                        "test1 shouldn't see because setting is too low",
+                        clusterApplierService.getClass().getName(),
+                        Level.WARN,
+                        "*cluster state applier task [test1] took [*] above the warn threshold of *"));
+        mockAppender.addExpectation(
+                new MockLogAppender.SeenEventExpectation(
+                        "test2",
+                        clusterApplierService.getClass().getName(),
+                        Level.WARN,
+                        "*cluster state applier task [test2] took [32s] above the warn threshold of *"));
+        mockAppender.addExpectation(
+                new MockLogAppender.SeenEventExpectation(
+                        "test4",
+                        clusterApplierService.getClass().getName(),
+                        Level.WARN,
+                        "*cluster state applier task [test3] took [34s] above the warn threshold of *"));
+
+        Logger clusterLogger = Loggers.getLogger("org.elasticsearch.cluster.service");
+        Loggers.addAppender(clusterLogger, mockAppender);
+        try {
+            final CountDownLatch latch = new CountDownLatch(4);
+            final CountDownLatch processedFirstTask = new CountDownLatch(1);
+            clusterApplierService.currentTimeOverride = System.nanoTime();
+            clusterApplierService.runOnApplierThread("test1",
+                currentState -> clusterApplierService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos(),
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                        processedFirstTask.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        fail();
+                    }
+                });
+            processedFirstTask.await();
+            clusterApplierService.runOnApplierThread("test2",
+                currentState -> {
+                    clusterApplierService.currentTimeOverride += TimeValue.timeValueSeconds(32).nanos();
+                    throw new IllegalArgumentException("Testing handling of exceptions in the cluster state task");
+                },
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        fail();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        latch.countDown();
+                    }
+                });
+            clusterApplierService.runOnApplierThread("test3",
+                currentState -> clusterApplierService.currentTimeOverride += TimeValue.timeValueSeconds(34).nanos(),
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        fail();
+                    }
+                });
+            // Additional update task to make sure all previous logging made it to the loggerName
+            // We don't check logging for this on since there is no guarantee that it will occur before our check
+            clusterApplierService.runOnApplierThread("test4",
+                currentState -> {},
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        fail();
+                    }
+                });
+            latch.await();
+        } finally {
+            Loggers.removeAppender(clusterLogger, mockAppender);
+            mockAppender.stop();
+        }
+        mockAppender.assertAllExpectationsMatched();
+    }
+
+    public void testLocalNodeMasterListenerCallbacks() throws Exception {
+        TimedClusterApplierService timedClusterApplierService = createTimedClusterService(false);
+
+        AtomicBoolean isMaster = new AtomicBoolean();
+        timedClusterApplierService.addLocalNodeMasterListener(new LocalNodeMasterListener() {
+            @Override
+            public void onMaster() {
+                isMaster.set(true);
+            }
+
+            @Override
+            public void offMaster() {
+                isMaster.set(false);
+            }
+
+            @Override
+            public String executorName() {
+                return ThreadPool.Names.SAME;
+            }
+        });
+
+        ClusterState state = timedClusterApplierService.state();
+        DiscoveryNodes nodes = state.nodes();
+        DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(nodes.getLocalNodeId());
+        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).nodes(nodesBuilder).build();
+        setState(timedClusterApplierService, state);
+        assertThat(isMaster.get(), is(true));
+
+        nodes = state.nodes();
+        nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(null);
+        state = ClusterState.builder(state).blocks(ClusterBlocks.builder().addGlobalBlock(DiscoverySettings.NO_MASTER_BLOCK_WRITES))
+            .nodes(nodesBuilder).build();
+        setState(timedClusterApplierService, state);
+        assertThat(isMaster.get(), is(false));
+        nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(nodes.getLocalNodeId());
+        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).nodes(nodesBuilder).build();
+        setState(timedClusterApplierService, state);
+        assertThat(isMaster.get(), is(true));
+
+        timedClusterApplierService.close();
+    }
+
+    public void testClusterStateApplierCantSampleClusterState() throws InterruptedException {
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        AtomicBoolean applierCalled = new AtomicBoolean();
+        clusterApplierService.addStateApplier(event -> {
+            try {
+                applierCalled.set(true);
+                clusterApplierService.state();
+                error.set(new AssertionError("successfully sampled state"));
+            } catch (AssertionError e) {
+                if (e.getMessage().contains("should not be called by a cluster state applier") == false) {
+                    error.set(e);
+                }
+            }
+        });
+
+        CountDownLatch latch = new CountDownLatch(1);
+        clusterApplierService.onNewClusterState("test", () -> ClusterState.builder(clusterApplierService.state()).build(),
+            new ClusterStateTaskListener() {
+
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    latch.countDown();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    error.compareAndSet(null, e);
+                }
+            }
+        );
+
+        latch.await();
+        assertNull(error.get());
+        assertTrue(applierCalled.get());
+    }
+
+    public void testClusterStateApplierCanCreateAnObserver() throws InterruptedException {
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        AtomicBoolean applierCalled = new AtomicBoolean();
+        clusterApplierService.addStateApplier(event -> {
+            try {
+                applierCalled.set(true);
+                ClusterStateObserver observer = new ClusterStateObserver(event.state(),
+                    clusterApplierService, null, logger, threadPool.getThreadContext());
+                observer.waitForNextChange(new ClusterStateObserver.Listener() {
+                    @Override
+                    public void onNewClusterState(ClusterState state) {
+
+                    }
+
+                    @Override
+                    public void onClusterServiceClose() {
+
+                    }
+
+                    @Override
+                    public void onTimeout(TimeValue timeout) {
+
+                    }
+                });
+            } catch (AssertionError e) {
+                error.set(e);
+            }
+        });
+
+        CountDownLatch latch = new CountDownLatch(1);
+        clusterApplierService.onNewClusterState("test", () -> ClusterState.builder(clusterApplierService.state()).build(),
+            new ClusterStateTaskListener() {
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    latch.countDown();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    error.compareAndSet(null, e);
+                }
+        });
+
+        latch.await();
+        assertNull(error.get());
+        assertTrue(applierCalled.get());
+    }
+
+    static class TimedClusterApplierService extends ClusterApplierService {
+
+        public volatile Long currentTimeOverride = null;
+
+        TimedClusterApplierService(Settings settings, ClusterSettings clusterSettings, ThreadPool threadPool) {
+            super(settings, clusterSettings, threadPool);
+        }
+
+        @Override
+        protected long currentTimeInNanos() {
+            if (currentTimeOverride != null) {
+                return currentTimeOverride;
+            }
+            return super.currentTimeInNanos();
+        }
+    }
+}

core/src/test/java/org/elasticsearch/cluster/service/ClusterServiceIT.java

@@ -382,7 +382,7 @@ public class ClusterServiceIT extends ESIntegTestCase {
 
         // The tasks can be re-ordered, so we need to check out-of-order
         Set<String> controlSources = new HashSet<>(Arrays.asList("1", "2", "3", "4", "5", "6", "7", "8", "9", "10"));
-        List<PendingClusterTask> pendingClusterTasks = clusterService.pendingTasks();
+        List<PendingClusterTask> pendingClusterTasks = clusterService.getMasterService().pendingTasks();
         assertThat(pendingClusterTasks.size(), greaterThanOrEqualTo(10));
         assertThat(pendingClusterTasks.get(0).getSource().string(), equalTo("1"));
         assertThat(pendingClusterTasks.get(0).isExecuting(), equalTo(true));
@@ -404,7 +404,7 @@ public class ClusterServiceIT extends ESIntegTestCase {
         invoked2.await();
 
         // whenever we test for no tasks, we need to awaitBusy since this is a live node
-        assertTrue(awaitBusy(() -> clusterService.pendingTasks().isEmpty()));
+        assertTrue(awaitBusy(() -> clusterService.getMasterService().pendingTasks().isEmpty()));
         waitNoPendingTasksOnAll();
 
         final CountDownLatch block2 = new CountDownLatch(1);
@@ -444,7 +444,7 @@ public class ClusterServiceIT extends ESIntegTestCase {
         }
         Thread.sleep(100);
 
-        pendingClusterTasks = clusterService.pendingTasks();
+        pendingClusterTasks = clusterService.getMasterService().pendingTasks();
         assertThat(pendingClusterTasks.size(), greaterThanOrEqualTo(5));
         controlSources = new HashSet<>(Arrays.asList("1", "2", "3", "4", "5"));
         for (PendingClusterTask task : pendingClusterTasks) {

core/src/test/java/org/elasticsearch/cluster/service/MasterServiceTests.java

@@ -20,32 +20,25 @@ package org.elasticsearch.cluster.service;
 
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.Logger;
-import org.apache.logging.log4j.util.Supplier;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.ClusterStateObserver;
 import org.elasticsearch.cluster.ClusterStateTaskConfig;
 import org.elasticsearch.cluster.ClusterStateTaskExecutor;
 import org.elasticsearch.cluster.ClusterStateTaskListener;
 import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.LocalClusterUpdateTask;
-import org.elasticsearch.cluster.LocalNodeMasterListener;
-import org.elasticsearch.cluster.NodeConnectionsService;
 import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.logging.Loggers;
-import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.concurrent.BaseFuture;
-import org.elasticsearch.common.util.set.Sets;
-import org.elasticsearch.discovery.Discovery;
-import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.MockLogAppender;
 import org.elasticsearch.test.junit.annotations.TestLogging;
@@ -75,21 +68,19 @@ import java.util.concurrent.atomic.AtomicReference;
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.emptySet;
-import static org.elasticsearch.test.ClusterServiceUtils.setState;
 import static org.hamcrest.Matchers.anyOf;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasKey;
-import static org.hamcrest.Matchers.is;
 
-public class ClusterServiceTests extends ESTestCase {
+public class MasterServiceTests extends ESTestCase {
 
-    static ThreadPool threadPool;
+    private static ThreadPool threadPool;
-    TimedClusterService clusterService;
+    private TimedMasterService masterService;
 
     @BeforeClass
     public static void createThreadPool() {
-        threadPool = new TestThreadPool(ClusterServiceTests.class.getName());
+        threadPool = new TestThreadPool(MasterServiceTests.class.getName());
     }
 
     @AfterClass
@@ -103,48 +94,35 @@ public class ClusterServiceTests extends ESTestCase {
     @Before
     public void setUp() throws Exception {
         super.setUp();
-        clusterService = createTimedClusterService(true);
+        masterService = createTimedMasterService(true);
     }
 
     @After
     public void tearDown() throws Exception {
-        clusterService.close();
+        masterService.close();
         super.tearDown();
     }
 
-    TimedClusterService createTimedClusterService(boolean makeMaster) throws InterruptedException {
+    private TimedMasterService createTimedMasterService(boolean makeMaster) throws InterruptedException {
-        TimedClusterService timedClusterService = new TimedClusterService(Settings.builder().put("cluster.name",
+        DiscoveryNode localNode = new DiscoveryNode("node1", buildNewFakeTransportAddress(), emptyMap(),
-            "ClusterServiceTests").build(), new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
+            emptySet(), Version.CURRENT);
-            threadPool, () -> new DiscoveryNode("node1", buildNewFakeTransportAddress(), emptyMap(),
+        TimedMasterService timedMasterService = new TimedMasterService(Settings.builder().put("cluster.name",
-            emptySet(), Version.CURRENT));
+            MasterServiceTests.class.getSimpleName()).build(), threadPool);
-        timedClusterService.setNodeConnectionsService(new NodeConnectionsService(Settings.EMPTY, null, null) {
+        ClusterState initialClusterState = ClusterState.builder(new ClusterName(MasterServiceTests.class.getSimpleName()))
-            @Override
+            .nodes(DiscoveryNodes.builder()
-            public void connectToNodes(DiscoveryNodes discoveryNodes) {
+                .add(localNode)
-                // skip
+                .localNodeId(localNode.getId())
-            }
+                .masterNodeId(makeMaster ? localNode.getId() : null))
-
+            .blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).build();
-            @Override
+        AtomicReference<ClusterState> clusterStateRef = new AtomicReference<>(initialClusterState);
-            public void disconnectFromNodesExcept(DiscoveryNodes nodesToKeep) {
+        timedMasterService.setClusterStatePublisher((event, ackListener) -> clusterStateRef.set(event.state()));
-                // skip
+        timedMasterService.setClusterStateSupplier(clusterStateRef::get);
-            }
+        timedMasterService.start();
-        });
+        return timedMasterService;
-        timedClusterService.setClusterStatePublisher((event, ackListener) -> {
-        });
-        timedClusterService.setDiscoverySettings(new DiscoverySettings(Settings.EMPTY,
-            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS)));
-        timedClusterService.start();
-        ClusterState state = timedClusterService.state();
-        final DiscoveryNodes nodes = state.nodes();
-        final DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(nodes)
-            .masterNodeId(makeMaster ? nodes.getLocalNodeId() : null);
-        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK)
-            .nodes(nodesBuilder).build();
-        setState(timedClusterService, state);
-        return timedClusterService;
     }
 
     public void testMasterAwareExecution() throws Exception {
-        ClusterService nonMaster = createTimedClusterService(false);
+        TimedMasterService nonMaster = createTimedMasterService(false);
 
         final boolean[] taskFailed = {false};
         final CountDownLatch latch1 = new CountDownLatch(1);
@@ -196,7 +174,7 @@ public class ClusterServiceTests extends ESTestCase {
         final CountDownLatch latch = new CountDownLatch(1);
         AtomicBoolean published = new AtomicBoolean();
 
-        clusterService.submitStateUpdateTask(
+        masterService.submitStateUpdateTask(
             "testClusterStateTaskListenerThrowingExceptionIsOkay",
             new Object(),
             ClusterStateTaskConfig.build(Priority.NORMAL),
@@ -229,49 +207,109 @@ public class ClusterServiceTests extends ESTestCase {
         assertTrue(published.get());
     }
 
-    public void testBlockingCallInClusterStateTaskListenerFails() throws InterruptedException {
+    @TestLogging("org.elasticsearch.cluster.service:TRACE") // To ensure that we log cluster state events on TRACE level
-        assumeTrue("assertions must be enabled for this test to work", BaseFuture.class.desiredAssertionStatus());
+    public void testClusterStateUpdateLogging() throws Exception {
-        final CountDownLatch latch = new CountDownLatch(1);
+        MockLogAppender mockAppender = new MockLogAppender();
-        final AtomicReference<AssertionError> assertionRef = new AtomicReference<>();
+        mockAppender.start();
+        mockAppender.addExpectation(
+            new MockLogAppender.SeenEventExpectation(
+                "test1",
+                masterService.getClass().getName(),
+                Level.DEBUG,
+                "*processing [test1]: took [1s] no change in cluster state"));
+        mockAppender.addExpectation(
+            new MockLogAppender.SeenEventExpectation(
+                "test2",
+                masterService.getClass().getName(),
+                Level.TRACE,
+                "*failed to execute cluster state update in [2s]*"));
+        mockAppender.addExpectation(
+            new MockLogAppender.SeenEventExpectation(
+                "test3",
+                masterService.getClass().getName(),
+                Level.DEBUG,
+                "*processing [test3]: took [3s] done publishing updated cluster state (version: *, uuid: *)"));
 
-        clusterService.submitStateUpdateTask(
+        Logger clusterLogger = Loggers.getLogger(masterService.getClass().getPackage().getName());
-            "testBlockingCallInClusterStateTaskListenerFails",
+        Loggers.addAppender(clusterLogger, mockAppender);
-            new Object(),
+        try {
-            ClusterStateTaskConfig.build(Priority.NORMAL),
+            final CountDownLatch latch = new CountDownLatch(4);
-            new ClusterStateTaskExecutor<Object>() {
+            masterService.currentTimeOverride = System.nanoTime();
+            masterService.submitStateUpdateTask("test1", new ClusterStateUpdateTask() {
                 @Override
-                public ClusterTasksResult<Object> execute(ClusterState currentState, List<Object> tasks) throws Exception {
+                public ClusterState execute(ClusterState currentState) throws Exception {
-                    ClusterState newClusterState = ClusterState.builder(currentState).build();
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos();
-                    return ClusterTasksResult.builder().successes(tasks).build(newClusterState);
+                    return currentState;
                 }
-            },
+
-            new ClusterStateTaskListener() {
                 @Override
                 public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                    BaseFuture<Void> future = new BaseFuture<Void>() {};
-                    try {
-                        if (randomBoolean()) {
-                            future.get(1L, TimeUnit.SECONDS);
-                        } else {
-                            future.get();
-                        }
-                    } catch (Exception e) {
-                        throw new RuntimeException(e);
-                    } catch (AssertionError e) {
-                        assertionRef.set(e);
                     latch.countDown();
                 }
-                }
 
                 @Override
                 public void onFailure(String source, Exception e) {
+                    fail();
                 }
+            });
+            masterService.submitStateUpdateTask("test2", new ClusterStateUpdateTask() {
+                @Override
+                public ClusterState execute(ClusterState currentState) {
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(2).nanos();
+                    throw new IllegalArgumentException("Testing handling of exceptions in the cluster state task");
                 }
-        );
 
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    fail();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    latch.countDown();
+                }
+            });
+            masterService.submitStateUpdateTask("test3", new ClusterStateUpdateTask() {
+                @Override
+                public ClusterState execute(ClusterState currentState) {
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(3).nanos();
+                    return ClusterState.builder(currentState).incrementVersion().build();
+                }
+
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    latch.countDown();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    fail();
+                }
+            });
+            // Additional update task to make sure all previous logging made it to the loggerName
+            // We don't check logging for this on since there is no guarantee that it will occur before our check
+            masterService.submitStateUpdateTask("test4", new ClusterStateUpdateTask() {
+                @Override
+                public ClusterState execute(ClusterState currentState) {
+                    return currentState;
+                }
+
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    latch.countDown();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    fail();
+                }
+            });
             latch.await();
-        assertNotNull(assertionRef.get());
+        } finally {
-        assertThat(assertionRef.get().getMessage(), containsString("not be the cluster state update thread. Reason: [Blocking operation]"));
+            Loggers.removeAppender(clusterLogger, mockAppender);
+            mockAppender.stop();
+        }
+        mockAppender.assertAllExpectationsMatched();
     }
 
     public void testClusterStateBatchedUpdates() throws BrokenBarrierException, InterruptedException {
@@ -414,7 +452,7 @@ public class ClusterServiceTests extends ESTestCase {
                         submittedTasksPerThread.computeIfAbsent(threadName, key -> new AtomicInteger()).addAndGet(tasks.size());
                         final TaskExecutor executor = assignment.v1();
                         if (tasks.size() == 1) {
-                            clusterService.submitStateUpdateTask(
+                            masterService.submitStateUpdateTask(
                                 threadName,
                                 tasks.stream().findFirst().get(),
                                 ClusterStateTaskConfig.build(randomFrom(Priority.values())),
@@ -423,7 +461,7 @@ public class ClusterServiceTests extends ESTestCase {
                         } else {
                             Map<Task, ClusterStateTaskListener> taskListeners = new HashMap<>();
                             tasks.stream().forEach(t -> taskListeners.put(t, listener));
-                            clusterService.submitStateUpdateTasks(
+                            masterService.submitStateUpdateTasks(
                                 threadName,
                                 taskListeners, ClusterStateTaskConfig.build(randomFrom(Priority.values())),
                                 executor
@@ -467,109 +505,47 @@ public class ClusterServiceTests extends ESTestCase {
         }
     }
 
-    @TestLogging("org.elasticsearch.cluster.service:TRACE") // To ensure that we log cluster state events on TRACE level
+    public void testBlockingCallInClusterStateTaskListenerFails() throws InterruptedException {
-    public void testClusterStateUpdateLogging() throws Exception {
+        assumeTrue("assertions must be enabled for this test to work", BaseFuture.class.desiredAssertionStatus());
-        MockLogAppender mockAppender = new MockLogAppender();
+        final CountDownLatch latch = new CountDownLatch(1);
-        mockAppender.start();
+        final AtomicReference<AssertionError> assertionRef = new AtomicReference<>();
-        mockAppender.addExpectation(
-                new MockLogAppender.SeenEventExpectation(
-                        "test1",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
-                        Level.DEBUG,
-                        "*processing [test1]: took [1s] no change in cluster_state"));
-        mockAppender.addExpectation(
-                new MockLogAppender.SeenEventExpectation(
-                        "test2",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
-                        Level.TRACE,
-                        "*failed to execute cluster state update in [2s]*"));
-        mockAppender.addExpectation(
-                new MockLogAppender.SeenEventExpectation(
-                        "test3",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
-                        Level.DEBUG,
-                        "*processing [test3]: took [3s] done applying updated cluster_state (version: *, uuid: *)"));
 
-        Logger clusterLogger = Loggers.getLogger("org.elasticsearch.cluster.service");
+        masterService.submitStateUpdateTask(
-        Loggers.addAppender(clusterLogger, mockAppender);
+            "testBlockingCallInClusterStateTaskListenerFails",
+            new Object(),
+            ClusterStateTaskConfig.build(Priority.NORMAL),
+            (currentState, tasks) -> {
+                ClusterState newClusterState = ClusterState.builder(currentState).build();
+                return ClusterStateTaskExecutor.ClusterTasksResult.builder().successes(tasks).build(newClusterState);
+            },
+            new ClusterStateTaskListener() {
+                @Override
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    BaseFuture<Void> future = new BaseFuture<Void>() {};
                     try {
-            final CountDownLatch latch = new CountDownLatch(4);
+                        if (randomBoolean()) {
-            clusterService.currentTimeOverride = System.nanoTime();
+                            future.get(1L, TimeUnit.SECONDS);
-            clusterService.submitStateUpdateTask("test1", new ClusterStateUpdateTask() {
+                        } else {
-                @Override
+                            future.get();
-                public ClusterState execute(ClusterState currentState) throws Exception {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos();
-                    return currentState;
                         }
-
+                    } catch (Exception e) {
-                @Override
+                        throw new RuntimeException(e);
-                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    } catch (AssertionError e) {
+                        assertionRef.set(e);
                         latch.countDown();
                     }
+                }
 
                 @Override
                 public void onFailure(String source, Exception e) {
-                    fail();
                 }
-            });
-            clusterService.submitStateUpdateTask("test2", new ClusterStateUpdateTask() {
-                @Override
-                public ClusterState execute(ClusterState currentState) {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(2).nanos();
-                    throw new IllegalArgumentException("Testing handling of exceptions in the cluster state task");
             }
+        );
 
-                @Override
-                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                    fail();
-                }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    latch.countDown();
-                }
-            });
-            clusterService.submitStateUpdateTask("test3", new ClusterStateUpdateTask() {
-                @Override
-                public ClusterState execute(ClusterState currentState) {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(3).nanos();
-                    return ClusterState.builder(currentState).incrementVersion().build();
-                }
-
-                @Override
-                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                    latch.countDown();
-                }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    fail();
-                }
-            });
-            // Additional update task to make sure all previous logging made it to the loggerName
-            // We don't check logging for this on since there is no guarantee that it will occur before our check
-            clusterService.submitStateUpdateTask("test4", new ClusterStateUpdateTask() {
-                @Override
-                public ClusterState execute(ClusterState currentState) {
-                    return currentState;
-                }
-
-                @Override
-                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                    latch.countDown();
-                }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    fail();
-                }
-            });
         latch.await();
-        } finally {
+        assertNotNull(assertionRef.get());
-            Loggers.removeAppender(clusterLogger, mockAppender);
+        assertThat(assertionRef.get().getMessage(),
-            mockAppender.stop();
+            containsString("Reason: [Blocking operation]"));
-        }
-        mockAppender.assertAllExpectationsMatched();
     }
 
     @TestLogging("org.elasticsearch.cluster.service:WARN") // To ensure that we log cluster state events on WARN level
@@ -579,38 +555,38 @@ public class ClusterServiceTests extends ESTestCase {
         mockAppender.addExpectation(
             new MockLogAppender.UnseenEventExpectation(
                 "test1 shouldn't see because setting is too low",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
+                masterService.getClass().getName(),
                 Level.WARN,
                 "*cluster state update task [test1] took [*] above the warn threshold of *"));
         mockAppender.addExpectation(
             new MockLogAppender.SeenEventExpectation(
                 "test2",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
+                masterService.getClass().getName(),
                 Level.WARN,
                 "*cluster state update task [test2] took [32s] above the warn threshold of *"));
         mockAppender.addExpectation(
             new MockLogAppender.SeenEventExpectation(
                 "test3",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
+                masterService.getClass().getName(),
                 Level.WARN,
                 "*cluster state update task [test3] took [33s] above the warn threshold of *"));
         mockAppender.addExpectation(
             new MockLogAppender.SeenEventExpectation(
                 "test4",
-                        "org.elasticsearch.cluster.service.ClusterServiceTests$TimedClusterService",
+                masterService.getClass().getName(),
                 Level.WARN,
                 "*cluster state update task [test4] took [34s] above the warn threshold of *"));
 
-        Logger clusterLogger = Loggers.getLogger("org.elasticsearch.cluster.service");
+        Logger clusterLogger = Loggers.getLogger(masterService.getClass().getPackage().getName());
         Loggers.addAppender(clusterLogger, mockAppender);
         try {
             final CountDownLatch latch = new CountDownLatch(5);
             final CountDownLatch processedFirstTask = new CountDownLatch(1);
-            clusterService.currentTimeOverride = System.nanoTime();
+            masterService.currentTimeOverride = System.nanoTime();
-            clusterService.submitStateUpdateTask("test1", new ClusterStateUpdateTask() {
+            masterService.submitStateUpdateTask("test1", new ClusterStateUpdateTask() {
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos();
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(1).nanos();
                     return currentState;
                 }
 
@@ -627,10 +603,10 @@ public class ClusterServiceTests extends ESTestCase {
             });
 
             processedFirstTask.await();
-            clusterService.submitStateUpdateTask("test2", new ClusterStateUpdateTask() {
+            masterService.submitStateUpdateTask("test2", new ClusterStateUpdateTask() {
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(32).nanos();
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(32).nanos();
                     throw new IllegalArgumentException("Testing handling of exceptions in the cluster state task");
                 }
 
@@ -644,10 +620,10 @@ public class ClusterServiceTests extends ESTestCase {
                     latch.countDown();
                 }
             });
-            clusterService.submitStateUpdateTask("test3", new ClusterStateUpdateTask() {
+            masterService.submitStateUpdateTask("test3", new ClusterStateUpdateTask() {
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(33).nanos();
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(33).nanos();
                     return ClusterState.builder(currentState).incrementVersion().build();
                 }
 
@@ -661,10 +637,10 @@ public class ClusterServiceTests extends ESTestCase {
                     fail();
                 }
             });
-            clusterService.submitStateUpdateTask("test4", new ClusterStateUpdateTask() {
+            masterService.submitStateUpdateTask("test4", new ClusterStateUpdateTask() {
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    clusterService.currentTimeOverride += TimeValue.timeValueSeconds(34).nanos();
+                    masterService.currentTimeOverride += TimeValue.timeValueSeconds(34).nanos();
                     return currentState;
                 }
 
@@ -680,7 +656,7 @@ public class ClusterServiceTests extends ESTestCase {
             });
             // Additional update task to make sure all previous logging made it to the loggerName
             // We don't check logging for this on since there is no guarantee that it will occur before our check
-            clusterService.submitStateUpdateTask("test5", new ClusterStateUpdateTask() {
+            masterService.submitStateUpdateTask("test5", new ClusterStateUpdateTask() {
                 @Override
                 public ClusterState execute(ClusterState currentState) {
                     return currentState;
@@ -704,211 +680,12 @@ public class ClusterServiceTests extends ESTestCase {
         mockAppender.assertAllExpectationsMatched();
     }
 
-    public void testDisconnectFromNewlyAddedNodesIfClusterStatePublishingFails() throws InterruptedException {
+    static class TimedMasterService extends MasterService {
-        TimedClusterService timedClusterService = new TimedClusterService(Settings.builder().put("cluster.name",
-            "ClusterServiceTests").build(), new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
-            threadPool, () -> new DiscoveryNode("node1", buildNewFakeTransportAddress(), emptyMap(),
-            emptySet(), Version.CURRENT));
-        Set<DiscoveryNode> currentNodes = new HashSet<>();
-        timedClusterService.setNodeConnectionsService(new NodeConnectionsService(Settings.EMPTY, null, null) {
-            @Override
-            public void connectToNodes(DiscoveryNodes discoveryNodes) {
-                discoveryNodes.forEach(currentNodes::add);
-            }
-
-            @Override
-            public void disconnectFromNodesExcept(DiscoveryNodes nodesToKeep) {
-                Set<DiscoveryNode> nodeSet = new HashSet<>();
-                nodesToKeep.iterator().forEachRemaining(nodeSet::add);
-                currentNodes.removeIf(node -> nodeSet.contains(node) == false);
-            }
-        });
-        AtomicBoolean failToCommit = new AtomicBoolean();
-        timedClusterService.setClusterStatePublisher((event, ackListener) -> {
-            if (failToCommit.get()) {
-                throw new Discovery.FailedToCommitClusterStateException("just to test this");
-            }
-        });
-        timedClusterService.setDiscoverySettings(new DiscoverySettings(Settings.EMPTY,
-            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS)));
-        timedClusterService.start();
-        ClusterState state = timedClusterService.state();
-        final DiscoveryNodes nodes = state.nodes();
-        final DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(nodes)
-            .masterNodeId(nodes.getLocalNodeId());
-        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK)
-            .nodes(nodesBuilder).build();
-        setState(timedClusterService, state);
-
-        assertThat(currentNodes, equalTo(Sets.newHashSet(timedClusterService.state().getNodes())));
-
-        final CountDownLatch latch = new CountDownLatch(1);
-
-        // try to add node when cluster state publishing fails
-        failToCommit.set(true);
-        timedClusterService.submitStateUpdateTask("test", new ClusterStateUpdateTask() {
-            @Override
-            public ClusterState execute(ClusterState currentState) throws Exception {
-                DiscoveryNode newNode = new DiscoveryNode("node2", buildNewFakeTransportAddress(), emptyMap(),
-                    emptySet(), Version.CURRENT);
-                return ClusterState.builder(currentState).nodes(DiscoveryNodes.builder(currentState.nodes()).add(newNode)).build();
-            }
-
-            @Override
-            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                latch.countDown();
-            }
-
-            @Override
-            public void onFailure(String source, Exception e) {
-                latch.countDown();
-            }
-        });
-
-        latch.await();
-        assertThat(currentNodes, equalTo(Sets.newHashSet(timedClusterService.state().getNodes())));
-        timedClusterService.close();
-    }
-
-    public void testLocalNodeMasterListenerCallbacks() throws Exception {
-        TimedClusterService timedClusterService = createTimedClusterService(false);
-
-        AtomicBoolean isMaster = new AtomicBoolean();
-        timedClusterService.addLocalNodeMasterListener(new LocalNodeMasterListener() {
-            @Override
-            public void onMaster() {
-                isMaster.set(true);
-            }
-
-            @Override
-            public void offMaster() {
-                isMaster.set(false);
-            }
-
-            @Override
-            public String executorName() {
-                return ThreadPool.Names.SAME;
-            }
-        });
-
-        ClusterState state = timedClusterService.state();
-        DiscoveryNodes nodes = state.nodes();
-        DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(nodes.getLocalNodeId());
-        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).nodes(nodesBuilder).build();
-        setState(timedClusterService, state);
-        assertThat(isMaster.get(), is(true));
-
-        nodes = state.nodes();
-        nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(null);
-        state = ClusterState.builder(state).blocks(ClusterBlocks.builder().addGlobalBlock(DiscoverySettings.NO_MASTER_BLOCK_WRITES))
-            .nodes(nodesBuilder).build();
-        setState(timedClusterService, state);
-        assertThat(isMaster.get(), is(false));
-        nodesBuilder = DiscoveryNodes.builder(nodes).masterNodeId(nodes.getLocalNodeId());
-        state = ClusterState.builder(state).blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).nodes(nodesBuilder).build();
-        setState(timedClusterService, state);
-        assertThat(isMaster.get(), is(true));
-
-        timedClusterService.close();
-    }
-
-    public void testClusterStateApplierCantSampleClusterState() throws InterruptedException {
-        AtomicReference<Throwable> error = new AtomicReference<>();
-        AtomicBoolean applierCalled = new AtomicBoolean();
-        clusterService.addStateApplier(event -> {
-            try {
-                applierCalled.set(true);
-                clusterService.state();
-                error.set(new AssertionError("successfully sampled state"));
-            } catch (AssertionError e) {
-                if (e.getMessage().contains("should not be called by a cluster state applier") == false) {
-                    error.set(e);
-                }
-            }
-        });
-
-        CountDownLatch latch = new CountDownLatch(1);
-        clusterService.submitStateUpdateTask("test", new ClusterStateUpdateTask() {
-            @Override
-            public ClusterState execute(ClusterState currentState) throws Exception {
-                return ClusterState.builder(currentState).build();
-            }
-
-            @Override
-            public void onFailure(String source, Exception e) {
-                error.compareAndSet(null, e);
-            }
-
-            @Override
-            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                latch.countDown();
-            }
-        });
-
-        latch.await();
-        assertNull(error.get());
-        assertTrue(applierCalled.get());
-    }
-
-    public void testClusterStateApplierCanCreateAnObserver() throws InterruptedException {
-        AtomicReference<Throwable> error = new AtomicReference<>();
-        AtomicBoolean applierCalled = new AtomicBoolean();
-        clusterService.addStateApplier(event -> {
-            try {
-                applierCalled.set(true);
-                ClusterStateObserver observer = new ClusterStateObserver(event.state(),
-                    clusterService, null, logger, threadPool.getThreadContext());
-                observer.waitForNextChange(new ClusterStateObserver.Listener() {
-                    @Override
-                    public void onNewClusterState(ClusterState state) {
-
-                    }
-
-                    @Override
-                    public void onClusterServiceClose() {
-
-                    }
-
-                    @Override
-                    public void onTimeout(TimeValue timeout) {
-
-                    }
-                });
-            } catch (AssertionError e) {
-                    error.set(e);
-            }
-        });
-
-        CountDownLatch latch = new CountDownLatch(1);
-        clusterService.submitStateUpdateTask("test", new ClusterStateUpdateTask() {
-            @Override
-            public ClusterState execute(ClusterState currentState) throws Exception {
-                return ClusterState.builder(currentState).build();
-            }
-
-            @Override
-            public void onFailure(String source, Exception e) {
-                error.compareAndSet(null, e);
-            }
-
-            @Override
-            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
-                latch.countDown();
-            }
-        });
-
-        latch.await();
-        assertNull(error.get());
-        assertTrue(applierCalled.get());
-    }
-
-    static class TimedClusterService extends ClusterService {
 
         public volatile Long currentTimeOverride = null;
 
-        TimedClusterService(Settings settings, ClusterSettings clusterSettings, ThreadPool threadPool,
+        TimedMasterService(Settings settings, ThreadPool threadPool) {
-                                   Supplier<DiscoveryNode> localNodeSupplier) {
+            super(settings, threadPool);
-            super(settings, clusterSettings, threadPool, localNodeSupplier);
         }
 
         @Override
@@ -919,4 +696,11 @@ public class ClusterServiceTests extends ESTestCase {
             return super.currentTimeInNanos();
         }
     }
+
+    /**
+     * Returns the cluster state that the master service uses (and that is provided by the discovery layer)
+     */
+    public static ClusterState discoveryState(MasterService masterService) {
+        return masterService.state();
+    }
 }

core/src/test/java/org/elasticsearch/cluster/settings/ClusterSettingsIT.java

@@ -29,6 +29,7 @@ import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeUnit;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.DiscoverySettings;
+import org.elasticsearch.discovery.zen.ZenDiscovery;
 import org.elasticsearch.indices.recovery.RecoverySettings;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.ESIntegTestCase.ClusterScope;
@@ -282,7 +283,7 @@ public class ClusterSettingsIT extends ESIntegTestCase {
         assertThat(discoverySettings.getPublishTimeout().seconds(), equalTo(1L));
     }
 
-    private DiscoverySettings getDiscoverySettings() {return internalCluster().getInstance(Discovery.class).getDiscoverySettings();}
+    private DiscoverySettings getDiscoverySettings() {return ((ZenDiscovery) internalCluster().getInstance(Discovery.class)).getDiscoverySettings();}
 
     public void testClusterUpdateSettingsWithBlocks() {
         String key1 = "cluster.routing.allocation.enable";

core/src/test/java/org/elasticsearch/discovery/DiscoveryModuleTests.java

@@ -18,47 +18,43 @@
  */
 package org.elasticsearch.discovery;
 
-import java.io.IOException;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.function.Function;
-import java.util.function.Supplier;
-
 import org.apache.lucene.util.IOUtils;
 import org.elasticsearch.Version;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.network.NetworkService;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.zen.UnicastHostsProvider;
 import org.elasticsearch.discovery.zen.ZenDiscovery;
-import org.elasticsearch.discovery.zen.ZenPing;
 import org.elasticsearch.plugins.DiscoveryPlugin;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.NoopDiscovery;
 import org.elasticsearch.test.transport.MockTransportService;
-import org.elasticsearch.threadpool.TestThreadPool;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 import org.junit.After;
 import org.junit.Before;
-import org.mockito.Mock;
+
-import org.mockito.Mockito;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Supplier;
 
 import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
 
 public class DiscoveryModuleTests extends ESTestCase {
 
     private TransportService transportService;
     private NamedWriteableRegistry namedWriteableRegistry;
-    private ClusterService clusterService;
+    private MasterService masterService;
+    private ClusterApplier clusterApplier;
     private ThreadPool threadPool;
+    private ClusterSettings clusterSettings;
 
     public interface DummyHostsProviderPlugin extends DiscoveryPlugin {
         Map<String, Supplier<UnicastHostsProvider>> impl();
@@ -74,7 +70,8 @@ public class DiscoveryModuleTests extends ESTestCase {
         @Override
         default Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                                    NamedWriteableRegistry namedWriteableRegistry,
-                                                                   ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                                   MasterService masterService, ClusterApplier clusterApplier,
+                                                                   ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
             return impl();
         }
     }
@@ -82,11 +79,11 @@ public class DiscoveryModuleTests extends ESTestCase {
     @Before
     public void setupDummyServices() {
         transportService = MockTransportService.createNewService(Settings.EMPTY, Version.CURRENT, null, null);
-        clusterService = mock(ClusterService.class);
+        masterService = mock(MasterService.class);
         namedWriteableRegistry = new NamedWriteableRegistry(Collections.emptyList());
-        ClusterSettings clusterSettings = new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
+        clusterApplier = mock(ClusterApplier.class);
-        when(clusterService.getClusterSettings()).thenReturn(clusterSettings);
         threadPool = mock(ThreadPool.class);
+        clusterSettings = new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
     }
 
     @After
@@ -95,7 +92,8 @@ public class DiscoveryModuleTests extends ESTestCase {
     }
 
     private DiscoveryModule newModule(Settings settings, List<DiscoveryPlugin> plugins) {
-        return new DiscoveryModule(settings, threadPool, transportService, namedWriteableRegistry, null, clusterService, plugins);
+        return new DiscoveryModule(settings, threadPool, transportService, namedWriteableRegistry, null, masterService,
+            clusterApplier, clusterSettings, plugins);
     }
 
     public void testDefaults() {

core/src/test/java/org/elasticsearch/discovery/DiscoveryWithServiceDisruptionsIT.java

@@ -447,6 +447,8 @@ public class DiscoveryWithServiceDisruptionsIT extends ESIntegTestCase {
         ensureGreen("test");
 
         // verify all cluster states are the same
+        // use assert busy to wait for cluster states to be applied (as publish_timeout has low value)
+        assertBusy(() -> {
             ClusterState state = null;
             for (String node : nodes) {
                 ClusterState nodeState = getNodeClusterState(node);
@@ -460,9 +462,7 @@ public class DiscoveryWithServiceDisruptionsIT extends ESIntegTestCase {
                     assertEquals("unequal node count", state.nodes().getSize(), nodeState.nodes().getSize());
                     assertEquals("different masters ", state.nodes().getMasterNodeId(), nodeState.nodes().getMasterNodeId());
                     assertEquals("different meta data version", state.metaData().version(), nodeState.metaData().version());
-                if (!state.routingTable().toString().equals(nodeState.routingTable().toString())) {
+                    assertEquals("different routing", state.routingTable().toString(), nodeState.routingTable().toString());
-                    fail("different routing");
-                }
                 } catch (AssertionError t) {
                     fail("failed comparing cluster state: " + t.getMessage() + "\n" +
                         "--- cluster state of node [" + nodes.get(0) + "]: ---\n" + state +
@@ -470,6 +470,7 @@ public class DiscoveryWithServiceDisruptionsIT extends ESIntegTestCase {
                 }
 
             }
+        });
     }
 
     /**

core/src/test/java/org/elasticsearch/discovery/ZenFaultDetectionTests.java

@@ -25,7 +25,6 @@ import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.breaker.CircuitBreaker;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
@@ -58,17 +57,14 @@ import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 
 import static java.util.Collections.singleton;
-import static org.elasticsearch.test.ClusterServiceUtils.createClusterService;
-import static org.elasticsearch.test.ClusterServiceUtils.setState;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 
 public class ZenFaultDetectionTests extends ESTestCase {
     protected ThreadPool threadPool;
-    protected ClusterService clusterServiceA;
-    protected ClusterService clusterServiceB;
     private CircuitBreakerService circuitBreakerService;
 
     protected static final Version version0 = Version.fromId(/*0*/99);
@@ -97,8 +93,6 @@ public class ZenFaultDetectionTests extends ESTestCase {
         settingsB = Settings.builder().put("node.name", "TS_B").put(settings).build();
         serviceB = build(settingsB, version1);
         nodeB = serviceB.getLocalDiscoNode();
-        clusterServiceA = createClusterService(settingsA, threadPool, nodeA);
-        clusterServiceB = createClusterService(settingsB, threadPool, nodeB);
 
         // wait till all nodes are properly connected and the event has been sent, so tests in this class
         // will not get this callback called on the connections done in this setup
@@ -133,8 +127,6 @@ public class ZenFaultDetectionTests extends ESTestCase {
         super.tearDown();
         serviceA.close();
         serviceB.close();
-        clusterServiceA.close();
-        clusterServiceB.close();
         terminate(threadPool);
     }
 
@@ -241,9 +233,9 @@ public class ZenFaultDetectionTests extends ESTestCase {
                 .put(FaultDetection.PING_INTERVAL_SETTING.getKey(), "5m").put("cluster.name", clusterName.value());
 
         final ClusterState state = ClusterState.builder(clusterName).nodes(buildNodesForA(false)).build();
-        setState(clusterServiceA, state);
+        AtomicReference<ClusterState> clusterStateSupplier = new AtomicReference<>(state);
         MasterFaultDetection masterFD = new MasterFaultDetection(settings.build(), threadPool, serviceA,
-            clusterServiceA);
+            clusterStateSupplier::get, null, clusterName);
         masterFD.restart(nodeB, "test");
 
         final String[] failureReason = new String[1];
@@ -278,7 +270,7 @@ public class ZenFaultDetectionTests extends ESTestCase {
             .put(FaultDetection.PING_INTERVAL_SETTING.getKey(), "1s")
             .put("cluster.name", clusterName.value()).build();
         final ClusterState stateNodeA = ClusterState.builder(clusterName).nodes(buildNodesForA(false)).build();
-        setState(clusterServiceA, stateNodeA);
+        AtomicReference<ClusterState> clusterStateSupplierA = new AtomicReference<>(stateNodeA);
 
         int minExpectedPings = 2;
 
@@ -289,14 +281,14 @@ public class ZenFaultDetectionTests extends ESTestCase {
         serviceB.addTracer(pingProbeB);
 
         MasterFaultDetection masterFDNodeA = new MasterFaultDetection(Settings.builder().put(settingsA).put(settings).build(),
-            threadPool, serviceA, clusterServiceA);
+            threadPool, serviceA, clusterStateSupplierA::get, null, clusterName);
         masterFDNodeA.restart(nodeB, "test");
 
         final ClusterState stateNodeB = ClusterState.builder(clusterName).nodes(buildNodesForB(true)).build();
-        setState(clusterServiceB, stateNodeB);
+        AtomicReference<ClusterState> clusterStateSupplierB = new AtomicReference<>(stateNodeB);
 
         MasterFaultDetection masterFDNodeB = new MasterFaultDetection(Settings.builder().put(settingsB).put(settings).build(),
-            threadPool, serviceB, clusterServiceB);
+            threadPool, serviceB, clusterStateSupplierB::get, null, clusterName);
         masterFDNodeB.restart(nodeB, "test");
 
         // let's do a few pings

core/src/test/java/org/elasticsearch/discovery/single/SingleNodeDiscoveryTests.java

@@ -21,14 +21,10 @@ package org.elasticsearch.discovery.single;
 
 import org.apache.lucene.util.IOUtils;
 import org.elasticsearch.Version;
-import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.ClusterStateObserver;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.common.unit.TimeValue;
-import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.transport.MockTransportService;
 import org.elasticsearch.threadpool.TestThreadPool;
@@ -36,7 +32,6 @@ import org.elasticsearch.threadpool.ThreadPool;
 
 import java.io.Closeable;
 import java.util.Stack;
-import java.util.concurrent.CountDownLatch;
 
 import static org.elasticsearch.test.ClusterServiceUtils.createClusterService;
 import static org.hamcrest.Matchers.equalTo;
@@ -57,37 +52,10 @@ public class SingleNodeDiscoveryTests extends ESTestCase {
             final ClusterService clusterService = createClusterService(threadPool, node);
             stack.push(clusterService);
             final SingleNodeDiscovery discovery =
-                    new SingleNodeDiscovery(Settings.EMPTY, clusterService);
+                    new SingleNodeDiscovery(Settings.EMPTY, transportService,
+                        clusterService.getClusterApplierService());
             discovery.startInitialJoin();
-
+            final DiscoveryNodes nodes = discovery.getInitialClusterState().nodes();
-            // we are racing against the initial join which is asynchronous so we use an observer
-            final ClusterState state = clusterService.state();
-            final ThreadContext threadContext = threadPool.getThreadContext();
-            final ClusterStateObserver observer =
-                    new ClusterStateObserver(state, clusterService, null, logger, threadContext);
-            if (state.nodes().getMasterNodeId() == null) {
-                final CountDownLatch latch = new CountDownLatch(1);
-                observer.waitForNextChange(new ClusterStateObserver.Listener() {
-                    @Override
-                    public void onNewClusterState(ClusterState state) {
-                        latch.countDown();
-                    }
-
-                    @Override
-                    public void onClusterServiceClose() {
-                        latch.countDown();
-                    }
-
-                    @Override
-                    public void onTimeout(TimeValue timeout) {
-                        assert false;
-                    }
-                }, s -> s.nodes().getMasterNodeId() != null);
-
-                latch.await();
-            }
-
-            final DiscoveryNodes nodes = clusterService.state().nodes();
             assertThat(nodes.getSize(), equalTo(1));
             assertThat(nodes.getMasterNode().getId(), equalTo(node.getId()));
         } finally {

core/src/test/java/org/elasticsearch/discovery/zen/NodeJoinControllerTests.java

@@ -22,8 +22,10 @@ import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.apache.logging.log4j.util.Supplier;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
+import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.NotMasterException;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
@@ -35,14 +37,14 @@ import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.ShardRoutingState;
 import org.elasticsearch.cluster.routing.TestShardRouting;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.MasterService;
-import org.elasticsearch.common.settings.ClusterSettings;
+import org.elasticsearch.cluster.service.MasterServiceTests;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.common.util.concurrent.BaseFuture;
-import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.index.shard.ShardId;
+import org.elasticsearch.test.ClusterServiceUtils;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.test.junit.annotations.TestLogging;
@@ -81,8 +83,7 @@ import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_VERSION_CREATED;
 import static org.elasticsearch.cluster.routing.RoutingTableTests.updateActiveAllocations;
-import static org.elasticsearch.test.ClusterServiceUtils.createClusterService;
+import static org.elasticsearch.cluster.service.MasterServiceTests.discoveryState;
-import static org.elasticsearch.test.ClusterServiceUtils.setState;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
@@ -93,12 +94,12 @@ public class NodeJoinControllerTests extends ESTestCase {
 
     private static ThreadPool threadPool;
 
-    private ClusterService clusterService;
+    private MasterService masterService;
     private NodeJoinController nodeJoinController;
 
     @BeforeClass
     public static void beforeClass() {
-        threadPool = new TestThreadPool("ShardReplicationTests");
+        threadPool = new TestThreadPool("NodeJoinControllerTests");
     }
 
     @AfterClass
@@ -110,25 +111,39 @@ public class NodeJoinControllerTests extends ESTestCase {
     @Before
     public void setUp() throws Exception {
         super.setUp();
-        clusterService = createClusterService(threadPool);
-        final DiscoveryNodes initialNodes = clusterService.state().nodes();
-        final DiscoveryNode localNode = initialNodes.getLocalNode();
-        // make sure we have a master
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(
-            DiscoveryNodes.builder(initialNodes).masterNodeId(localNode.getId())));
-        nodeJoinController = new NodeJoinController(clusterService, createAllocationService(Settings.EMPTY),
-            new ElectMasterService(Settings.EMPTY), Settings.EMPTY);
     }
 
     @After
     public void tearDown() throws Exception {
         super.tearDown();
-        clusterService.close();
+        masterService.close();
+    }
+
+    private static ClusterState initialState(boolean withMaster) {
+        DiscoveryNode localNode = new DiscoveryNode("node", ESTestCase.buildNewFakeTransportAddress(), Collections.emptyMap(),
+            new HashSet<>(Arrays.asList(DiscoveryNode.Role.values())),Version.CURRENT);
+        ClusterState initialClusterState = ClusterState.builder(new ClusterName(ClusterServiceUtils.class.getSimpleName()))
+            .nodes(DiscoveryNodes.builder()
+                .add(localNode)
+                .localNodeId(localNode.getId())
+                .masterNodeId(withMaster ? localNode.getId() : null))
+            .blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).build();
+        return initialClusterState;
+    }
+
+    private void setupMasterServiceAndNodeJoinController(ClusterState initialState) {
+        if (masterService != null || nodeJoinController != null) {
+            throw new IllegalStateException("method setupMasterServiceAndNodeJoinController can only be called once");
+        }
+        masterService = ClusterServiceUtils.createMasterService(threadPool, initialState);
+        nodeJoinController = new NodeJoinController(masterService, createAllocationService(Settings.EMPTY),
+            new ElectMasterService(Settings.EMPTY), Settings.EMPTY);
     }
 
     public void testSimpleJoinAccumulation() throws InterruptedException, ExecutionException {
+        setupMasterServiceAndNodeJoinController(initialState(true));
         List<DiscoveryNode> nodes = new ArrayList<>();
-        nodes.add(clusterService.localNode());
+        nodes.add(discoveryState(masterService).nodes().getLocalNode());
 
         int nodeId = 0;
         for (int i = randomInt(5); i > 0; i--) {
@@ -162,9 +177,7 @@ public class NodeJoinControllerTests extends ESTestCase {
     }
 
     public void testFailingJoinsWhenNotMaster() throws ExecutionException, InterruptedException {
-        // remove current master flag
+        setupMasterServiceAndNodeJoinController(initialState(false));
-        DiscoveryNodes.Builder nodes = DiscoveryNodes.builder(clusterService.state().nodes()).masterNodeId(null);
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodes));
         int nodeId = 0;
         try {
             joinNode(newNode(nodeId++));
@@ -194,8 +207,7 @@ public class NodeJoinControllerTests extends ESTestCase {
     }
 
     public void testSimpleMasterElectionWithoutRequiredJoins() throws InterruptedException, ExecutionException {
-        DiscoveryNodes.Builder nodes = DiscoveryNodes.builder(clusterService.state().nodes()).masterNodeId(null);
+        setupMasterServiceAndNodeJoinController(initialState(false));
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodes));
         int nodeId = 0;
         final int requiredJoins = 0;
         logger.debug("--> using requiredJoins [{}]", requiredJoins);
@@ -244,8 +256,7 @@ public class NodeJoinControllerTests extends ESTestCase {
     }
 
     public void testSimpleMasterElection() throws InterruptedException, ExecutionException {
-        DiscoveryNodes.Builder nodes = DiscoveryNodes.builder(clusterService.state().nodes()).masterNodeId(null);
+        setupMasterServiceAndNodeJoinController(initialState(false));
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodes));
         int nodeId = 0;
         final int requiredJoins = 1 + randomInt(5);
         logger.debug("--> using requiredJoins [{}]", requiredJoins);
@@ -356,10 +367,8 @@ public class NodeJoinControllerTests extends ESTestCase {
 
     }
 
-
     public void testMasterElectionTimeout() throws InterruptedException {
-        DiscoveryNodes.Builder nodes = DiscoveryNodes.builder(clusterService.state().nodes()).masterNodeId(null);
+        setupMasterServiceAndNodeJoinController(initialState(false));
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodes));
         int nodeId = 0;
         final int requiredJoins = 1 + randomInt(5);
         logger.debug("--> using requiredJoins [{}]", requiredJoins);
@@ -422,22 +431,23 @@ public class NodeJoinControllerTests extends ESTestCase {
     }
 
     public void testNewClusterStateOnExistingNodeJoin() throws InterruptedException, ExecutionException {
-        ClusterState state = clusterService.state();
+        ClusterState state = initialState(true);
         final DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(state.nodes());
         final DiscoveryNode other_node = new DiscoveryNode("other_node", buildNewFakeTransportAddress(),
             emptyMap(), emptySet(), Version.CURRENT);
         nodesBuilder.add(other_node);
-        setState(clusterService, ClusterState.builder(state).nodes(nodesBuilder));
+        setupMasterServiceAndNodeJoinController(ClusterState.builder(state).nodes(nodesBuilder).build());
 
-        state = clusterService.state();
+        state = discoveryState(masterService);
         joinNode(other_node);
-        assertTrue("failed to publish a new state upon existing join", clusterService.state() != state);
+        assertTrue("failed to publish a new state upon existing join", discoveryState(masterService) != state);
     }
 
     public void testNormalConcurrentJoins() throws InterruptedException {
+        setupMasterServiceAndNodeJoinController(initialState(true));
         Thread[] threads = new Thread[3 + randomInt(5)];
         ArrayList<DiscoveryNode> nodes = new ArrayList<>();
-        nodes.add(clusterService.localNode());
+        nodes.add(discoveryState(masterService).nodes().getLocalNode());
         final CyclicBarrier barrier = new CyclicBarrier(threads.length);
         final List<Throwable> backgroundExceptions = new CopyOnWriteArrayList<>();
         for (int i = 0; i < threads.length; i++) {
@@ -472,15 +482,14 @@ public class NodeJoinControllerTests extends ESTestCase {
     }
 
     public void testElectionWithConcurrentJoins() throws InterruptedException, BrokenBarrierException {
-        DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(clusterService.state().nodes()).masterNodeId(null);
+        setupMasterServiceAndNodeJoinController(initialState(false));
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodesBuilder));
 
         nodeJoinController.startElectionContext();
 
         Thread[] threads = new Thread[3 + randomInt(5)];
         final int requiredJoins = randomInt(threads.length);
         ArrayList<DiscoveryNode> nodes = new ArrayList<>();
-        nodes.add(clusterService.localNode());
+        nodes.add(discoveryState(masterService).nodes().getLocalNode());
         final CyclicBarrier barrier = new CyclicBarrier(threads.length + 1);
         final List<Throwable> backgroundExceptions = new CopyOnWriteArrayList<>();
         for (int i = 0; i < threads.length; i++) {
@@ -539,7 +548,7 @@ public class NodeJoinControllerTests extends ESTestCase {
 
     public void testRejectingJoinWithSameAddressButDifferentId() throws InterruptedException, ExecutionException {
         addNodes(randomInt(5));
-        ClusterState state = clusterService.state();
+        ClusterState state = discoveryState(masterService);
         final DiscoveryNode existing = randomFrom(StreamSupport.stream(state.nodes().spliterator(), false).collect(Collectors.toList()));
         final DiscoveryNode other_node = new DiscoveryNode("other_node", existing.getAddress(), emptyMap(), emptySet(), Version.CURRENT);
 
@@ -549,7 +558,7 @@ public class NodeJoinControllerTests extends ESTestCase {
 
     public void testRejectingJoinWithSameIdButDifferentNode() throws InterruptedException, ExecutionException {
         addNodes(randomInt(5));
-        ClusterState state = clusterService.state();
+        ClusterState state = discoveryState(masterService);
         final DiscoveryNode existing = randomFrom(StreamSupport.stream(state.nodes().spliterator(), false).collect(Collectors.toList()));
         final DiscoveryNode other_node = new DiscoveryNode(
             randomBoolean() ? existing.getName() : "other_name",
@@ -565,7 +574,7 @@ public class NodeJoinControllerTests extends ESTestCase {
 
     public void testRejectingRestartedNodeJoinsBeforeProcessingNodeLeft() throws InterruptedException, ExecutionException {
         addNodes(randomInt(5));
-        ClusterState state = clusterService.state();
+        ClusterState state = discoveryState(masterService);
         final DiscoveryNode existing = randomFrom(StreamSupport.stream(state.nodes().spliterator(), false).collect(Collectors.toList()));
         joinNode(existing); // OK
 
@@ -581,15 +590,16 @@ public class NodeJoinControllerTests extends ESTestCase {
      * nodes that conflict with the joins it got and needs to become a master
      */
     public void testElectionBasedOnConflictingNodes() throws InterruptedException, ExecutionException {
-        final DiscoveryNode masterNode = clusterService.localNode();
+        ClusterState initialState = initialState(true);
+        final DiscoveryNode masterNode = initialState.nodes().getLocalNode();
         final DiscoveryNode otherNode = new DiscoveryNode("other_node", buildNewFakeTransportAddress(), emptyMap(),
             EnumSet.allOf(DiscoveryNode.Role.class), Version.CURRENT);
         // simulate master going down with stale nodes in it's cluster state (for example when min master nodes is set to 2)
         // also add some shards to that node
-        DiscoveryNodes.Builder discoBuilder = DiscoveryNodes.builder(clusterService.state().nodes());
+        DiscoveryNodes.Builder discoBuilder = DiscoveryNodes.builder(initialState.nodes());
         discoBuilder.masterNodeId(null);
         discoBuilder.add(otherNode);
-        ClusterState.Builder stateBuilder = ClusterState.builder(clusterService.state()).nodes(discoBuilder);
+        ClusterState.Builder stateBuilder = ClusterState.builder(initialState).nodes(discoBuilder);
         if (randomBoolean()) {
             IndexMetaData indexMetaData = IndexMetaData.builder("test").settings(Settings.builder()
                 .put(SETTING_VERSION_CREATED, Version.CURRENT)
@@ -623,7 +633,7 @@ public class NodeJoinControllerTests extends ESTestCase {
                         .routingTable(RoutingTable.builder().add(indexRoutingTable).build());
         }
 
-        setState(clusterService, stateBuilder.build());
+        setupMasterServiceAndNodeJoinController(stateBuilder.build());
 
         // conflict on node id or address
         final DiscoveryNode conflictingNode = randomBoolean() ?
@@ -652,7 +662,7 @@ public class NodeJoinControllerTests extends ESTestCase {
 
         joinFuture.get(); // throw any exception
 
-        final ClusterState finalState = clusterService.state();
+        final ClusterState finalState = discoveryState(masterService);
         final DiscoveryNodes finalNodes = finalState.nodes();
         assertTrue(finalNodes.isLocalNodeElectedMaster());
         assertThat(finalNodes.getLocalNode(), equalTo(masterNode));
@@ -666,18 +676,18 @@ public class NodeJoinControllerTests extends ESTestCase {
 
 
     private void addNodes(int count) {
-        ClusterState state = clusterService.state();
+        ClusterState state = initialState(true);
         final DiscoveryNodes.Builder nodesBuilder = DiscoveryNodes.builder(state.nodes());
         for (int i = 0;i< count;i++) {
             final DiscoveryNode node = new DiscoveryNode("node_" + state.nodes().getSize() + i, buildNewFakeTransportAddress(),
                 emptyMap(), new HashSet<>(randomSubsetOf(Arrays.asList(DiscoveryNode.Role.values()))), Version.CURRENT);
             nodesBuilder.add(node);
         }
-        setState(clusterService, ClusterState.builder(state).nodes(nodesBuilder));
+        setupMasterServiceAndNodeJoinController(ClusterState.builder(state).nodes(nodesBuilder).build());
     }
 
     protected void assertNodesInCurrentState(List<DiscoveryNode> expectedNodes) {
-        final ClusterState state = clusterService.state();
+        final ClusterState state = discoveryState(masterService);
         logger.info("assert for [{}] in:\n{}", expectedNodes, state);
         DiscoveryNodes discoveryNodes = state.nodes();
         for (DiscoveryNode node : expectedNodes) {

core/src/test/java/org/elasticsearch/discovery/zen/ZenDiscoveryIT.java

@@ -260,6 +260,7 @@ public class ZenDiscoveryIT extends ESIntegTestCase {
                 "}";
 
         internalCluster().startNode();
+        ensureGreen(); // ensures that all events are processed (in particular state recovery fully completed)
 
         logger.info("--> request node discovery stats");
         NodesStatsResponse statsResponse = client().admin().cluster().prepareNodesStats().clear().setDiscovery(true).get();

core/src/test/java/org/elasticsearch/discovery/zen/ZenDiscoveryUnitTests.java

@@ -37,12 +37,14 @@ import org.elasticsearch.cluster.routing.RoutingTable;
 import org.elasticsearch.cluster.routing.ShardRoutingState;
 import org.elasticsearch.cluster.routing.TestShardRouting;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.zen.PublishClusterStateActionTests.AssertingAckListener;
 import org.elasticsearch.index.shard.ShardId;
+import org.elasticsearch.test.ClusterServiceUtils;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.test.transport.MockTransportService;
@@ -65,6 +67,7 @@ import java.util.List;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
 import static java.util.Collections.emptyMap;
@@ -74,9 +77,9 @@ import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_VERSION_CREATED;
 import static org.elasticsearch.cluster.routing.RoutingTableTests.updateActiveAllocations;
+import static org.elasticsearch.cluster.service.MasterServiceTests.discoveryState;
 import static org.elasticsearch.discovery.zen.ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING;
 import static org.elasticsearch.discovery.zen.ZenDiscovery.shouldIgnoreOrRejectNewClusterState;
-import static org.elasticsearch.test.ClusterServiceUtils.createClusterService;
 import static org.elasticsearch.test.ClusterServiceUtils.setState;
 import static org.hamcrest.Matchers.arrayWithSize;
 import static org.hamcrest.Matchers.containsString;
@@ -182,26 +185,31 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
             DiscoveryNode masterNode = masterTransport.getLocalNode();
             toClose.addFirst(masterTransport);
             ClusterState state = ClusterStateCreationUtils.state(masterNode, masterNode, masterNode);
-            // build the zen discovery and cluster service
+            // build the zen discovery and discovery service
-            ClusterService masterClusterService = createClusterService(threadPool, masterNode);
+            MasterService masterMasterService = ClusterServiceUtils.createMasterService(threadPool, masterNode);
-            toClose.addFirst(masterClusterService);
+            toClose.addFirst(masterMasterService);
             // TODO: clustername shouldn't be stored twice in cluster service, but for now, work around it
-            state = ClusterState.builder(masterClusterService.getClusterName()).nodes(state.nodes()).build();
+            state = ClusterState.builder(discoveryState(masterMasterService).getClusterName()).nodes(state.nodes()).build();
-            setState(masterClusterService, state);
+            Settings settingsWithClusterName = Settings.builder().put(settings).put(
-            ZenDiscovery masterZen = buildZenDiscovery(settings, masterTransport, masterClusterService, threadPool);
+                ClusterName.CLUSTER_NAME_SETTING.getKey(), discoveryState(masterMasterService).getClusterName().value()).build();
+            ZenDiscovery masterZen = buildZenDiscovery(
+                settingsWithClusterName,
+                masterTransport, masterMasterService, threadPool);
+            masterZen.setState(state);
             toClose.addFirst(masterZen);
             masterTransport.acceptIncomingRequests();
 
             final MockTransportService otherTransport = MockTransportService.createNewService(settings, Version.CURRENT, threadPool, null);
             otherTransport.start();
             toClose.addFirst(otherTransport);
+
             DiscoveryNode otherNode = otherTransport.getLocalNode();
-            final ClusterState otherState = ClusterState.builder(masterClusterService.getClusterName())
+            final ClusterState otherState = ClusterState.builder(discoveryState(masterMasterService).getClusterName())
                 .nodes(DiscoveryNodes.builder().add(otherNode).localNodeId(otherNode.getId())).build();
-            ClusterService otherClusterService = createClusterService(threadPool, masterNode);
+            MasterService otherMasterService = ClusterServiceUtils.createMasterService(threadPool, otherNode);
-            toClose.addFirst(otherClusterService);
+            toClose.addFirst(otherMasterService);
-            setState(otherClusterService, otherState);
+            ZenDiscovery otherZen = buildZenDiscovery(settingsWithClusterName, otherTransport, otherMasterService, threadPool);
-            ZenDiscovery otherZen = buildZenDiscovery(settings, otherTransport, otherClusterService, threadPool);
+            otherZen.setState(otherState);
             toClose.addFirst(otherZen);
             otherTransport.acceptIncomingRequests();
 
@@ -210,7 +218,7 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
 
             // a new cluster state with a new discovery node (we will test if the cluster state
             // was updated by the presence of this node in NodesFaultDetection)
-            ClusterState newState = ClusterState.builder(masterClusterService.state()).incrementVersion().nodes(
+            ClusterState newState = ClusterState.builder(discoveryState(masterMasterService)).incrementVersion().nodes(
                 DiscoveryNodes.builder(state.nodes()).add(otherNode).masterNodeId(masterNode.getId())
             ).build();
 
@@ -220,7 +228,7 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
                 AssertingAckListener listener = new AssertingAckListener(newState.nodes().getSize() - 1);
                 expectedFDNodes = masterZen.getFaultDetectionNodes();
                 masterZen.publish(clusterChangedEvent, listener);
-                listener.await(1, TimeUnit.HOURS);
+                listener.await(10, TimeUnit.SECONDS);
                 // publish was a success, update expected FD nodes based on new cluster state
                 expectedFDNodes = fdNodesForState(newState, masterNode);
             } catch (Discovery.FailedToCommitClusterStateException e) {
@@ -249,12 +257,12 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
             DiscoveryNode masterNode = masterTransport.getLocalNode();
             toClose.addFirst(masterTransport);
             ClusterState state = ClusterStateCreationUtils.state(masterNode, null, masterNode);
-            // build the zen discovery and cluster service
+            // build the zen discovery and master service for the master node
-            ClusterService masterClusterService = createClusterService(threadPool, masterNode);
+            MasterService masterMasterService = ClusterServiceUtils.createMasterService(threadPool, masterNode);
-            toClose.addFirst(masterClusterService);
+            toClose.addFirst(masterMasterService);
-            state = ClusterState.builder(masterClusterService.getClusterName()).nodes(state.nodes()).build();
+            state = ClusterState.builder(discoveryState(masterMasterService).getClusterName()).nodes(state.nodes()).build();
-            setState(masterClusterService, state);
+            ZenDiscovery masterZen = buildZenDiscovery(settings, masterTransport, masterMasterService, threadPool);
-            ZenDiscovery masterZen = buildZenDiscovery(settings, masterTransport, masterClusterService, threadPool);
+            masterZen.setState(state);
             toClose.addFirst(masterZen);
             masterTransport.acceptIncomingRequests();
 
@@ -263,8 +271,8 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
 
             // a new cluster state with a new discovery node (we will test if the cluster state
             // was updated by the presence of this node in NodesFaultDetection)
-            ClusterState newState = ClusterState.builder(masterClusterService.state()).incrementVersion().nodes(
+            ClusterState newState = ClusterState.builder(discoveryState(masterMasterService)).incrementVersion().nodes(
-                DiscoveryNodes.builder(masterClusterService.state().nodes()).masterNodeId(masterNode.getId())
+                DiscoveryNodes.builder(discoveryState(masterMasterService).nodes()).masterNodeId(masterNode.getId())
             ).build();
 
 
@@ -277,9 +285,8 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
                 // publish was a success, check that queue as cleared
                 assertThat(masterZen.pendingClusterStates(), emptyArray());
             } catch (Discovery.FailedToCommitClusterStateException e) {
-                // not successful, so the pending queue should stay
+                // not successful, so the pending queue should be cleaned
-                assertThat(masterZen.pendingClusterStates(), arrayWithSize(1));
+                assertThat(Arrays.toString(masterZen.pendingClusterStates()), masterZen.pendingClusterStates(), arrayWithSize(0));
-                assertThat(masterZen.pendingClusterStates()[0].getClusterName().value(), equalTo("foreign"));
             }
         } finally {
             IOUtils.close(toClose);
@@ -287,9 +294,12 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
         }
     }
 
-    private ZenDiscovery buildZenDiscovery(Settings settings, TransportService service, ClusterService clusterService, ThreadPool threadPool) {
+    private ZenDiscovery buildZenDiscovery(Settings settings, TransportService service, MasterService masterService,
+                                           ThreadPool threadPool) {
+        ClusterSettings clusterSettings = new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
         ZenDiscovery zenDiscovery = new ZenDiscovery(settings, threadPool, service, new NamedWriteableRegistry(ClusterModule.getNamedWriteables()),
-            clusterService, Collections::emptyList);
+            masterService, (source, clusterStateSupplier, listener) -> listener.clusterStateProcessed(source, clusterStateSupplier.get(), clusterStateSupplier.get()),
+            clusterSettings, Collections::emptyList);
         zenDiscovery.start();
         return zenDiscovery;
     }

core/src/test/java/org/elasticsearch/gateway/GatewayServiceTests.java

@@ -19,10 +19,7 @@
 
 package org.elasticsearch.gateway;
 
-import org.elasticsearch.Version;
-import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
@@ -37,7 +34,7 @@ public class GatewayServiceTests extends ESTestCase {
     private GatewayService createService(Settings.Builder settings) {
         ClusterService clusterService = new ClusterService(Settings.builder().put("cluster.name", "GatewayServiceTests").build(),
                 new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
-                null, () -> new DiscoveryNode(UUIDs.randomBase64UUID(), buildNewFakeTransportAddress(), Version.CURRENT));
+                null);
         return new GatewayService(settings.build(),
                 null, clusterService, null, null, null, new NoopDiscovery(), null);
     }

core/src/test/java/org/elasticsearch/indexlifecycle/IndexLifecycleActionIT.java

@@ -32,6 +32,7 @@ import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.ESIntegTestCase.ClusterScope;
 import org.elasticsearch.test.ESIntegTestCase.Scope;
 import org.elasticsearch.test.InternalTestCluster;
+import org.elasticsearch.transport.TransportService;
 
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -204,8 +205,8 @@ public class IndexLifecycleActionIT extends ESIntegTestCase {
     }
 
     private String getLocalNodeId(String name) {
-        Discovery discovery = internalCluster().getInstance(Discovery.class, name);
+        TransportService transportService = internalCluster().getInstance(TransportService.class, name);
-        String nodeId = discovery.localNode().getId();
+        String nodeId = transportService.getLocalNode().getId();
         assertThat(nodeId, not(nullValue()));
         return nodeId;
     }

core/src/test/java/org/elasticsearch/indices/store/IndicesStoreIntegrationIT.java

@@ -20,9 +20,12 @@
 package org.elasticsearch.indices.store;
 
 import org.apache.logging.log4j.Logger;
+import org.elasticsearch.ExceptionsHelper;
+import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.admin.cluster.health.ClusterHealthResponse;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
 import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.health.ClusterHealthStatus;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
@@ -35,6 +38,7 @@ import org.elasticsearch.cluster.routing.ShardRoutingState;
 import org.elasticsearch.cluster.routing.TestShardRouting;
 import org.elasticsearch.cluster.routing.allocation.command.MoveAllocationCommand;
 import org.elasticsearch.cluster.routing.allocation.decider.EnableAllocationDecider;
+import org.elasticsearch.cluster.service.ClusterApplierService;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.settings.Settings;
@@ -434,26 +438,35 @@ public class IndicesStoreIntegrationIT extends ESIntegTestCase {
         // disable relocations when we do this, to make sure the shards are not relocated from node2
         // due to rebalancing, and delete its content
         client().admin().cluster().prepareUpdateSettings().setTransientSettings(Settings.builder().put(EnableAllocationDecider.CLUSTER_ROUTING_REBALANCE_ENABLE_SETTING.getKey(), EnableAllocationDecider.Rebalance.NONE)).get();
-        internalCluster().getInstance(ClusterService.class, nonMasterNode).submitStateUpdateTask("test", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+
-            @Override
+        ClusterApplierService clusterApplierService = internalCluster().getInstance(ClusterService.class, nonMasterNode).getClusterApplierService();
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
+        ClusterState currentState = clusterApplierService.state();
         IndexRoutingTable.Builder indexRoutingTableBuilder = IndexRoutingTable.builder(index);
-                for (int i = 0; i < numShards; i++) {
+        for (int j = 0; j < numShards; j++) {
             indexRoutingTableBuilder.addIndexShard(
-                            new IndexShardRoutingTable.Builder(new ShardId(index, i))
+                new IndexShardRoutingTable.Builder(new ShardId(index, j))
-                                    .addShard(TestShardRouting.newShardRouting("test", i, masterId, true, ShardRoutingState.STARTED))
+                    .addShard(TestShardRouting.newShardRouting("test", j, masterId, true, ShardRoutingState.STARTED))
                     .build()
             );
         }
-                return newState(ClusterState.builder(currentState)
+        ClusterState newState = ClusterState.builder(currentState)
+            .incrementVersion()
             .routingTable(RoutingTable.builder().add(indexRoutingTableBuilder).build())
-                        .build());
+            .build();
+        CountDownLatch latch = new CountDownLatch(1);
+        clusterApplierService.onNewClusterState("test", () -> newState, new ClusterStateTaskListener() {
+            @Override
+            public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                latch.countDown();
             }
 
             @Override
             public void onFailure(String source, Exception e) {
+                latch.countDown();
+                fail("Excepted proper response " + ExceptionsHelper.detailedMessage(e));
             }
         });
+        latch.await();
         waitNoPendingTasksOnAll();
         logger.info("Checking if shards aren't removed");
         for (int shard : node2Shards) {

core/src/test/java/org/elasticsearch/search/aggregations/metrics/GeoCentroidIT.java

@@ -59,6 +59,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         assertThat(geoCentroid.getName(), equalTo(aggName));
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid, equalTo(null));
+        assertEquals(0, geoCentroid.count());
     }
 
     public void testUnmapped() throws Exception {
@@ -72,6 +73,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         assertThat(geoCentroid.getName(), equalTo(aggName));
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid, equalTo(null));
+        assertEquals(0, geoCentroid.count());
     }
 
     public void testPartiallyUnmapped() throws Exception {
@@ -86,6 +88,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, geoCentroid.count());
     }
 
     public void testSingleValuedField() throws Exception {
@@ -101,6 +104,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, geoCentroid.count());
     }
 
     public void testSingleValueFieldGetProperty() throws Exception {
@@ -130,6 +134,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
                 closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
         assertThat((double) ((InternalAggregation)global).getProperty(aggName + ".lat"), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat((double) ((InternalAggregation)global).getProperty(aggName + ".lon"), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, (long) ((InternalAggregation) global).getProperty(aggName + ".count"));
     }
 
     public void testMultiValuedField() throws Exception {
@@ -145,6 +150,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(multiCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(multiCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(2 * numDocs, geoCentroid.count());
     }
 
     public void testSingleValueFieldAsSubAggToGeohashGrid() throws Exception {

core/src/test/java/org/elasticsearch/search/aggregations/metrics/geocentroid/InternalGeoCentroidTests.java

@@ -42,8 +42,11 @@ public class InternalGeoCentroidTests extends InternalAggregationTestCase<Intern
         centroid.resetLon(GeoEncodingUtils.decodeLongitude(encodedLon));
         int encodedLat = GeoEncodingUtils.encodeLatitude(centroid.lat());
         centroid.resetLat(GeoEncodingUtils.decodeLatitude(encodedLat));
-
+        long count = randomIntBetween(0, 1000);
-        return new InternalGeoCentroid("_name", centroid, 1, Collections.emptyList(), Collections.emptyMap());
+        if (count == 0) {
+            centroid = null;
+        }
+        return new InternalGeoCentroid("_name", centroid, count, Collections.emptyList(), Collections.emptyMap());
     }
 
     @Override
@@ -53,14 +56,18 @@ public class InternalGeoCentroidTests extends InternalAggregationTestCase<Intern
 
     @Override
     protected void assertReduced(InternalGeoCentroid reduced, List<InternalGeoCentroid> inputs) {
-        GeoPoint expected = new GeoPoint(0, 0);
+        double lonSum = 0;
-        int i = 0;
+        double latSum = 0;
+        int totalCount = 0;
         for (InternalGeoCentroid input : inputs) {
-            expected.reset(expected.lat() + (input.centroid().lat() - expected.lat()) / (i+1),
+            if (input.count() > 0) {
-                    expected.lon() + (input.centroid().lon() - expected.lon()) / (i+1));
+                lonSum += (input.count() * input.centroid().getLon());
-            i++;
+                latSum += (input.count() * input.centroid().getLat());
             }
-        assertEquals(expected.getLat(), reduced.centroid().getLat(), 1E-5D);
+            totalCount += input.count();
-        assertEquals(expected.getLon(), reduced.centroid().getLon(), 1E-5D);
+        }
+        assertEquals(latSum/totalCount, reduced.centroid().getLat(), 1E-5D);
+        assertEquals(lonSum/totalCount, reduced.centroid().getLon(), 1E-5D);
+        assertEquals(totalCount, reduced.count());
     }
 }

core/src/test/java/org/elasticsearch/snapshots/AbstractSnapshotIntegTestCase.java

@@ -18,19 +18,9 @@
  */
 package org.elasticsearch.snapshots;
 
-import org.apache.logging.log4j.message.ParameterizedMessage;
-import org.apache.logging.log4j.util.Supplier;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
-import org.elasticsearch.action.admin.cluster.tasks.PendingClusterTasksResponse;
-import org.elasticsearch.cluster.ClusterChangedEvent;
-import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.ClusterStateListener;
-import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.SnapshotsInProgress;
 import org.elasticsearch.cluster.routing.allocation.decider.EnableAllocationDecider;
-import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.cluster.service.PendingClusterTask;
-import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.plugins.Plugin;
@@ -47,13 +37,10 @@ import java.nio.file.attribute.BasicFileAttributes;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
-import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.function.Predicate;
 
 import static org.hamcrest.Matchers.equalTo;
-import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 
 public abstract class AbstractSnapshotIntegTestCase extends ESIntegTestCase {
 
@@ -180,121 +167,4 @@ public abstract class AbstractSnapshotIntegTestCase extends ESIntegTestCase {
     public static void unblockNode(final String repository, final String node) {
         ((MockRepository)internalCluster().getInstance(RepositoriesService.class, node).repository(repository)).unblock();
     }
-
-    protected void assertBusyPendingTasks(final String taskPrefix, final int expectedCount) throws Exception {
-        assertBusy(new Runnable() {
-            @Override
-            public void run() {
-                PendingClusterTasksResponse tasks = client().admin().cluster().preparePendingClusterTasks().get();
-                int count = 0;
-                for(PendingClusterTask task : tasks) {
-                    if (task.getSource().toString().startsWith(taskPrefix)) {
-                        count++;
-                    }
-                }
-                assertThat(count, greaterThanOrEqualTo(expectedCount));
-            }
-        }, 1, TimeUnit.MINUTES);
-    }
-
-    /**
-     * Cluster state task that blocks waits for the blockOn task to show up and then blocks execution not letting
-     * any cluster state update task to be performed unless they have priority higher then passThroughPriority.
-     *
-     * This class is useful to testing of cluster state update task batching for lower priority tasks.
-     */
-    protected class BlockingClusterStateListener implements ClusterStateListener {
-
-        private final Predicate<ClusterChangedEvent> blockOn;
-        private final Predicate<ClusterChangedEvent> countOn;
-        private final ClusterService clusterService;
-        private final CountDownLatch latch;
-        private final Priority passThroughPriority;
-        private int count;
-        private boolean timedOut;
-        private final TimeValue timeout;
-        private long stopWaitingAt = -1;
-
-        public BlockingClusterStateListener(ClusterService clusterService, String blockOn, String countOn, Priority passThroughPriority) {
-            // Waiting for the 70 seconds here to make sure that the last check at 65 sec mark in assertBusyPendingTasks has a chance
-            // to finish before we timeout on the cluster state block. Otherwise the last check in assertBusyPendingTasks kicks in
-            // after the cluster state block clean up takes place and it's assert doesn't reflect the actual failure
-            this(clusterService, blockOn, countOn, passThroughPriority, TimeValue.timeValueSeconds(70));
-        }
-
-        public BlockingClusterStateListener(ClusterService clusterService, final String blockOn, final String countOn, Priority passThroughPriority, TimeValue timeout) {
-            this.clusterService = clusterService;
-            this.blockOn = clusterChangedEvent -> clusterChangedEvent.source().startsWith(blockOn);
-            this.countOn = clusterChangedEvent -> clusterChangedEvent.source().startsWith(countOn);
-            this.latch = new CountDownLatch(1);
-            this.passThroughPriority = passThroughPriority;
-            this.timeout = timeout;
-
-        }
-
-        public void unblock() {
-            latch.countDown();
-        }
-
-        @Override
-        public void clusterChanged(ClusterChangedEvent event) {
-            if (blockOn.test(event)) {
-                logger.info("blocking cluster state tasks on [{}]", event.source());
-                assert stopWaitingAt < 0; // Make sure we are the first time here
-                stopWaitingAt = System.currentTimeMillis() + timeout.getMillis();
-                addBlock();
-            }
-            if (countOn.test(event)) {
-                count++;
-            }
-        }
-
-        private void addBlock() {
-            // We should block after this task - add blocking cluster state update task
-            clusterService.submitStateUpdateTask("test_block", new ClusterStateUpdateTask(passThroughPriority) {
-                @Override
-                public ClusterState execute(ClusterState currentState) throws Exception {
-                    while(System.currentTimeMillis() < stopWaitingAt) {
-                        for (PendingClusterTask task : clusterService.pendingTasks()) {
-                            if (task.getSource().string().equals("test_block") == false && passThroughPriority.sameOrAfter(task.getPriority())) {
-                                // There are other higher priority tasks in the queue and let them pass through and then set the block again
-                                logger.info("passing through cluster state task {}", task.getSource());
-                                addBlock();
-                                return currentState;
-                            }
-                        }
-                        try {
-                            logger.info("waiting....");
-                            if (latch.await(Math.min(100, timeout.millis()), TimeUnit.MILLISECONDS)){
-                                // Done waiting - unblock
-                                logger.info("unblocked");
-                                return currentState;
-                            }
-                            logger.info("done waiting....");
-                        } catch (InterruptedException ex) {
-                            logger.info("interrupted....");
-                            Thread.currentThread().interrupt();
-                            return currentState;
-                        }
-                    }
-                    timedOut = true;
-                    return currentState;
-                }
-
-                @Override
-                public void onFailure(String source, Exception e) {
-                    logger.warn((Supplier<?>) () -> new ParameterizedMessage("failed to execute [{}]", source), e);
-                }
-            });
-
-        }
-
-        public int count() {
-            return count;
-        }
-
-        public boolean timedOut() {
-            return timedOut;
-        }
-    }
 }

core/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java

@@ -724,14 +724,9 @@ public class DedicatedClusterSnapshotRestoreIT extends AbstractSnapshotIntegTest
     }
 
     public void testMasterShutdownDuringSnapshot() throws Exception {
-        Settings masterSettings = Settings.builder().put(Node.NODE_DATA_SETTING.getKey(), false).build();
-        Settings dataSettings = Settings.builder().put(Node.NODE_MASTER_SETTING.getKey(), false).build();
-
         logger.info("-->  starting two master nodes and two data nodes");
-        internalCluster().startNode(masterSettings);
+        internalCluster().startMasterOnlyNodes(2);
-        internalCluster().startNode(masterSettings);
+        internalCluster().startDataOnlyNodes(2);
-        internalCluster().startNode(dataSettings);
-        internalCluster().startNode(dataSettings);
 
         final Client client = client();
 
@@ -758,35 +753,17 @@ public class DedicatedClusterSnapshotRestoreIT extends AbstractSnapshotIntegTest
         final int numberOfShards = getNumShards("test-idx").numPrimaries;
         logger.info("number of shards: {}", numberOfShards);
 
-        final ClusterService clusterService = internalCluster().clusterService(internalCluster().getMasterName());
-        BlockingClusterStateListener snapshotListener = new BlockingClusterStateListener(clusterService, "update_snapshot [", "update snapshot state", Priority.HIGH);
-        try {
-            clusterService.addListener(snapshotListener);
-            logger.info("--> snapshot");
         dataNodeClient().admin().cluster().prepareCreateSnapshot("test-repo", "test-snap").setWaitForCompletion(false).setIndices("test-idx").get();
 
-            // Await until some updates are in pending state.
-            assertBusyPendingTasks("update snapshot state", 1);
-
         logger.info("--> stopping master node");
         internalCluster().stopCurrentMasterNode();
 
-            logger.info("--> unblocking snapshot execution");
-            snapshotListener.unblock();
-
-        } finally {
-            clusterService.removeListener(snapshotListener);
-        }
-
         logger.info("--> wait until the snapshot is done");
 
-        assertBusy(new Runnable() {
+        assertBusy(() -> {
-            @Override
-            public void run() {
             GetSnapshotsResponse snapshotsStatusResponse = client().admin().cluster().prepareGetSnapshots("test-repo").setSnapshots("test-snap").get();
             SnapshotInfo snapshotInfo = snapshotsStatusResponse.getSnapshots().get(0);
             assertTrue(snapshotInfo.state().completed());
-            }
         }, 1, TimeUnit.MINUTES);
 
         logger.info("--> verify that snapshot was succesful");

core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java

@@ -2286,59 +2286,6 @@ public class SharedClusterSnapshotRestoreIT extends AbstractSnapshotIntegTestCas
         return awaitBusy(() -> client().admin().cluster().prepareHealth(index).execute().actionGet().getRelocatingShards() > 0, timeout.millis(), TimeUnit.MILLISECONDS);
     }
 
-    public void testBatchingShardUpdateTask() throws Exception {
-        final Client client = client();
-
-        logger.info("-->  creating repository");
-        assertAcked(client.admin().cluster().preparePutRepository("test-repo")
-                .setType("fs").setSettings(Settings.builder()
-                        .put("location", randomRepoPath())
-                        .put("compress", randomBoolean())
-                        .put("chunk_size", randomIntBetween(100, 1000), ByteSizeUnit.BYTES)));
-
-        assertAcked(prepareCreate("test-idx", 0, Settings.builder().put("number_of_shards", between(1, 10))
-                .put("number_of_replicas", 0)));
-        ensureGreen();
-
-        logger.info("--> indexing some data");
-        final int numdocs = randomIntBetween(10, 100);
-        IndexRequestBuilder[] builders = new IndexRequestBuilder[numdocs];
-        for (int i = 0; i < builders.length; i++) {
-            builders[i] = client().prepareIndex("test-idx", "type1", Integer.toString(i)).setSource("field1", "bar " + i);
-        }
-        indexRandom(true, builders);
-        flushAndRefresh();
-
-        final int numberOfShards = getNumShards("test-idx").numPrimaries;
-        logger.info("number of shards: {}", numberOfShards);
-
-        final ClusterService clusterService = internalCluster().clusterService(internalCluster().getMasterName());
-        BlockingClusterStateListener snapshotListener = new BlockingClusterStateListener(clusterService, "update_snapshot [", "update snapshot state", Priority.HIGH);
-        try {
-            clusterService.addListener(snapshotListener);
-            logger.info("--> snapshot");
-            ListenableActionFuture<CreateSnapshotResponse> snapshotFuture = client.admin().cluster().prepareCreateSnapshot("test-repo", "test-snap").setWaitForCompletion(true).setIndices("test-idx").execute();
-
-            // Await until shard updates are in pending state.
-            assertBusyPendingTasks("update snapshot state", numberOfShards);
-            snapshotListener.unblock();
-
-            // Check that the snapshot was successful
-            CreateSnapshotResponse createSnapshotResponse = snapshotFuture.actionGet();
-            assertEquals(SnapshotState.SUCCESS, createSnapshotResponse.getSnapshotInfo().state());
-            assertEquals(numberOfShards, createSnapshotResponse.getSnapshotInfo().totalShards());
-            assertEquals(numberOfShards, createSnapshotResponse.getSnapshotInfo().successfulShards());
-
-        } finally {
-            clusterService.removeListener(snapshotListener);
-        }
-
-        // Check that we didn't timeout
-        assertFalse(snapshotListener.timedOut());
-        // Check that cluster state update task was called only once
-        assertEquals(1, snapshotListener.count());
-    }
-
     public void testSnapshotName() throws Exception {
         final Client client = client();
 

core/src/test/java/org/elasticsearch/test/NoopDiscovery.java

@@ -19,27 +19,15 @@
 package org.elasticsearch.test;
 
 import org.elasticsearch.cluster.ClusterChangedEvent;
-import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
 import org.elasticsearch.common.component.Lifecycle;
 import org.elasticsearch.common.component.LifecycleListener;
 import org.elasticsearch.discovery.Discovery;
-import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.discovery.DiscoveryStats;
 
 public class NoopDiscovery implements Discovery {
 
-
-    @Override
-    public DiscoveryNode localNode() {
-        return null;
-    }
-
-    @Override
-    public String nodeDescription() {
-        return null;
-    }
-
     @Override
     public void setAllocationService(AllocationService allocationService) {
 
@@ -51,12 +39,17 @@ public class NoopDiscovery implements Discovery {
     }
 
     @Override
-    public DiscoveryStats stats() {
+    public ClusterState getInitialClusterState() {
         return null;
     }
 
     @Override
-    public DiscoverySettings getDiscoverySettings() {
+    public ClusterState clusterState() {
+        return null;
+    }
+
+    @Override
+    public DiscoveryStats stats() {
         return null;
     }
 

core/src/test/java/org/elasticsearch/update/UpdateIT.java

@@ -492,60 +492,6 @@ public class UpdateIT extends ESIntegTestCase {
         assertThat(updateResponse.getGetResult().sourceAsMap().get("extra").toString(), equalTo("foo"));
     }
     
-    public void testVersionedUpdate() throws Exception {
-        assertAcked(prepareCreate("test").addAlias(new Alias("alias")));
-        ensureGreen();
-
-        index("test", "type", "1", "text", "value"); // version is now 1
-
-        assertThrows(client().prepareUpdate(indexOrAlias(), "type", "1")
-                        .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v2"))).setVersion(2)
-                        .execute(),
-                VersionConflictEngineException.class);
-
-        client().prepareUpdate(indexOrAlias(), "type", "1")
-                .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v2"))).setVersion(1).get();
-        assertThat(client().prepareGet("test", "type", "1").get().getVersion(), equalTo(2L));
-
-        // and again with a higher version..
-        client().prepareUpdate(indexOrAlias(), "type", "1")
-                .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v3"))).setVersion(2).get();
-
-        assertThat(client().prepareGet("test", "type", "1").get().getVersion(), equalTo(3L));
-
-        // after delete
-        client().prepareDelete("test", "type", "1").get();
-        assertThrows(client().prepareUpdate("test", "type", "1")
-                        .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v2"))).setVersion(3)
-                        .execute(),
-                DocumentMissingException.class);
-
-        // external versioning
-        client().prepareIndex("test", "type", "2").setSource("text", "value").setVersion(10).setVersionType(VersionType.EXTERNAL).get();
-
-        assertThrows(client().prepareUpdate(indexOrAlias(), "type", "2")
-                        .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v2"))).setVersion(2)
-                        .setVersionType(VersionType.EXTERNAL).execute(),
-                ActionRequestValidationException.class);
-
-        GetResponse get = get("test", "type", "2");
-        assertThat(get.getVersion(), equalTo(10L));
-        assertThat((String) get.getSource().get("text"), equalTo("value"));
-
-        // upserts - the combination with versions is a bit weird. Test are here to ensure we do not change our behavior unintentionally
-
-        // With internal versions, tt means "if object is there with version X, update it or explode. If it is not there, index.
-        client().prepareUpdate(indexOrAlias(), "type", "3")
-                .setScript(new Script(ScriptType.INLINE, "put_values", "", Collections.singletonMap("text", "v2")))
-                .setVersion(10).setUpsert("{ \"text\": \"v0\" }", XContentType.JSON).get();
-        get = get("test", "type", "3");
-        assertThat(get.getVersion(), equalTo(1L));
-        assertThat((String) get.getSource().get("text"), equalTo("v0"));
-
-        // retry on conflict is rejected:
-        assertThrows(client().prepareUpdate(indexOrAlias(), "type", "1").setVersion(10).setRetryOnConflict(5), ActionRequestValidationException.class);
-    }
-
     public void testIndexAutoCreation() throws Exception {
         UpdateResponse updateResponse = client().prepareUpdate("test", "type1", "1")
                 .setUpsert(XContentFactory.jsonBuilder().startObject().field("bar", "baz").endObject())

docs/reference/aggregations/metrics/geocentroid-aggregation.asciidoc

@@ -62,7 +62,8 @@ The response for the above aggregation:
             "location": {
                 "lat": 51.00982963107526,
                 "lon": 3.9662130922079086
-            }
+            },
+            "count": 6
         }
     }
 }
@@ -114,7 +115,8 @@ The response for the above aggregation:
                       "location": {
                          "lat": 52.371655656024814,
                          "lon": 4.909563297405839
-                      }
+                      },
+                      "count": 3
                    }
                },
                {
@@ -124,7 +126,8 @@ The response for the above aggregation:
                       "location": {
                          "lat": 48.86055548675358,
                          "lon": 2.3316944623366
-                      }
+                      },
+                      "count": 2
                    }
                 },
                 {
@@ -134,7 +137,8 @@ The response for the above aggregation:
                        "location": {
                           "lat": 51.22289997059852,
                           "lon": 4.40519998781383
-                       }
+                       },
+                       "count": 1
                     }
                  }
             ]

docs/reference/cat/alias.asciidoc

@@ -54,5 +54,6 @@ alias4 test1 -      2            1,2
 The output shows that `alias2` has configured a filter, and specific routing
 configurations in `alias3` and `alias4`.
 
-If you only want to get information about a single alias, you can specify
+If you only want to get information about specific aliases, you can specify 
-the alias in the URL, for example `/_cat/aliases/alias1`.
+the aliases in comma-delimited format as a URL parameter, e.g., 
+/_cat/aliases/aliases/alias1,alias2.

docs/reference/cat/health.asciidoc

@@ -16,7 +16,8 @@ GET /_cat/health?v
 epoch      timestamp cluster       status node.total node.data shards pri relo init unassign pending_tasks max_task_wait_time active_shards_percent
 1475871424 16:17:04  elasticsearch green           1         1      5   5    0    0        0             0                  -                100.0%
 --------------------------------------------------
-// TESTRESPONSE[s/1475871424 16:17:04/\\d+ \\d+:\\d+:\\d+/ s/elasticsearch/[^ ]+/ s/0                  -/\\d+ -/ _cat]
+// TESTRESPONSE[s/1475871424 16:17:04/\\d+ \\d+:\\d+:\\d+/]
+// TESTRESPONSE[s/elasticsearch/[^ ]+/ s/0                  -/\\d+ (-|\\d+(\\.\\d+)?[ms]+)/ _cat]
 
 It has one option `ts` to disable the timestamping:
 
@@ -34,7 +35,7 @@ which looks like:
 cluster       status node.total node.data shards pri relo init unassign pending_tasks max_task_wait_time active_shards_percent
 elasticsearch green           1         1      5   5    0    0        0             0                  -                100.0%
 --------------------------------------------------
-// TESTRESPONSE[s/elasticsearch/[^ ]+/ s/0                  -/\\d+ -/ _cat]
+// TESTRESPONSE[s/elasticsearch/[^ ]+/ s/0                  -/\\d+ (-|\\d+(\\.\\d+)?[ms]+)/ _cat]
 
 A common use of this command is to verify the health is consistent
 across nodes:

docs/reference/migration/migrate_6_0/docs.asciidoc

@@ -5,3 +5,7 @@
 
 Document modification operations may no longer specify the `version_type` of
 `force` to override any previous version checks.
+
+==== <<upserts>> no longer support versions
+
+Adding a `version` to an upsert request is no longer supported.

docs/reference/search/request/inner-hits.asciidoc

@@ -148,6 +148,55 @@ An important default is that the `_source` returned in hits inside `inner_hits`
 So in the above example only the comment part is returned per nested hit and not the entire source of the top level
 document that contained the comment.
 
+[[nested-inner-hits-source]]
+==== Nested inner hits and _source
+
+Nested document don't have a `_source` field, because the entire source of document is stored with the root document under
+its `_source` field. To include the source of just the nested document, the source of the root document is parsed and just
+the relevant bit for the nested document is included as source in the inner hit. Doing this for each matching nested document
+has an impact on the time it takes to execute the entire search request, especially when `size` and the inner hits' `size`
+are set higher than the default. To avoid the relative expensive source extraction for nested inner hits, one can disable
+including the source and solely rely on stored fields.
+
+Enabled stored field for fields under the nested object field in your mapping:
+
+[source,js]
+--------------------------------------------------
+{
+    "properties": {
+        "comment": {
+          "type": "comments",
+          "properties" : {
+            "message" : {
+                "type" : "text",
+                "store" : true
+            }
+          }
+        }
+    }
+}
+--------------------------------------------------
+
+Disable including source and include specific stored fields in the inner hits definition:
+
+[source,js]
+--------------------------------------------------
+{
+    "query" : {
+        "nested" : {
+            "path" : "comments",
+            "query" : {
+                "match" : {"comments.message" : "[actual query]"}
+            },
+            "inner_hits" : {
+                "_source" : false,
+                "stored_fields" : ["comments.text"]
+            }
+        }
+    }
+}
+--------------------------------------------------
+
 [[hierarchical-nested-inner-hits]]
 ==== Hierarchical levels of nested object fields and inner hits.
 

plugins/discovery-azure-classic/src/main/java/org/elasticsearch/plugin/discovery/azure/classic/AzureDiscoveryPlugin.java

@@ -19,22 +19,16 @@
 
 package org.elasticsearch.plugin.discovery.azure.classic;
 
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.Map;
-import java.util.function.Supplier;
-
 import org.apache.logging.log4j.Logger;
-import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.cloud.azure.classic.management.AzureComputeService;
 import org.elasticsearch.cloud.azure.classic.management.AzureComputeServiceImpl;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
-import org.elasticsearch.common.Strings;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
@@ -42,12 +36,17 @@ import org.elasticsearch.discovery.DiscoveryModule;
 import org.elasticsearch.discovery.azure.classic.AzureUnicastHostsProvider;
 import org.elasticsearch.discovery.zen.UnicastHostsProvider;
 import org.elasticsearch.discovery.zen.ZenDiscovery;
-import org.elasticsearch.discovery.zen.ZenPing;
 import org.elasticsearch.plugins.DiscoveryPlugin;
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Supplier;
+
 public class AzureDiscoveryPlugin extends Plugin implements DiscoveryPlugin {
 
     public static final String AZURE = "azure";
@@ -76,10 +75,12 @@ public class AzureDiscoveryPlugin extends Plugin implements DiscoveryPlugin {
     @Override
     public Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                               NamedWriteableRegistry namedWriteableRegistry,
-                                                              ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                              MasterService masterService, ClusterApplier clusterApplier,
+                                                              ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
         // this is for backcompat with pre 5.1, where users would set discovery.type to use ec2 hosts provider
         return Collections.singletonMap(AZURE, () ->
-            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider));
+            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, masterService, clusterApplier,
+                clusterSettings, hostsProvider));
     }
 
     @Override

plugins/discovery-ec2/src/main/java/org/elasticsearch/discovery/ec2/Ec2DiscoveryPlugin.java

@@ -20,6 +20,30 @@
 package org.elasticsearch.discovery.ec2;
 
 import com.amazonaws.util.json.Jackson;
+import org.apache.logging.log4j.Logger;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.SetOnce;
+import org.elasticsearch.SpecialPermission;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.common.SuppressForbidden;
+import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
+import org.elasticsearch.common.logging.DeprecationLogger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.ClusterSettings;
+import org.elasticsearch.common.settings.Setting;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.discovery.Discovery;
+import org.elasticsearch.discovery.DiscoveryModule;
+import org.elasticsearch.cluster.service.MasterService;
+import org.elasticsearch.discovery.zen.UnicastHostsProvider;
+import org.elasticsearch.discovery.zen.ZenDiscovery;
+import org.elasticsearch.node.Node;
+import org.elasticsearch.plugins.DiscoveryPlugin;
+import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.threadpool.ThreadPool;
+import org.elasticsearch.transport.TransportService;
+
 import java.io.BufferedReader;
 import java.io.Closeable;
 import java.io.IOException;
@@ -37,28 +61,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.function.Supplier;
 
-import org.apache.logging.log4j.Logger;
-import org.apache.lucene.util.IOUtils;
-import org.apache.lucene.util.SetOnce;
-import org.elasticsearch.SpecialPermission;
-import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.common.SuppressForbidden;
-import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
-import org.elasticsearch.common.logging.DeprecationLogger;
-import org.elasticsearch.common.logging.Loggers;
-import org.elasticsearch.common.network.NetworkService;
-import org.elasticsearch.common.settings.Setting;
-import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.discovery.Discovery;
-import org.elasticsearch.discovery.DiscoveryModule;
-import org.elasticsearch.discovery.zen.UnicastHostsProvider;
-import org.elasticsearch.discovery.zen.ZenDiscovery;
-import org.elasticsearch.node.Node;
-import org.elasticsearch.plugins.DiscoveryPlugin;
-import org.elasticsearch.plugins.Plugin;
-import org.elasticsearch.threadpool.ThreadPool;
-import org.elasticsearch.transport.TransportService;
-
 public class Ec2DiscoveryPlugin extends Plugin implements DiscoveryPlugin, Closeable {
 
     private static Logger logger = Loggers.getLogger(Ec2DiscoveryPlugin.class);
@@ -95,10 +97,12 @@ public class Ec2DiscoveryPlugin extends Plugin implements DiscoveryPlugin, Close
     @Override
     public Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                               NamedWriteableRegistry namedWriteableRegistry,
-                                                              ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                              MasterService masterService, ClusterApplier clusterApplier,
+                                                              ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
         // this is for backcompat with pre 5.1, where users would set discovery.type to use ec2 hosts provider
         return Collections.singletonMap(EC2, () ->
-            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider));
+            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, masterService, clusterApplier,
+                clusterSettings, hostsProvider));
     }
 
     @Override

plugins/discovery-gce/src/main/java/org/elasticsearch/plugin/discovery/gce/GceDiscoveryPlugin.java

@@ -24,28 +24,25 @@ import com.google.api.client.util.ClassInfo;
 import org.apache.logging.log4j.Logger;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.SetOnce;
-import org.elasticsearch.SpecialPermission;
 import org.elasticsearch.cloud.gce.GceInstancesService;
 import org.elasticsearch.cloud.gce.GceInstancesServiceImpl;
 import org.elasticsearch.cloud.gce.GceMetadataService;
-import org.elasticsearch.cloud.gce.GceModule;
 import org.elasticsearch.cloud.gce.network.GceNameResolver;
 import org.elasticsearch.cloud.gce.util.Access;
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
-import org.elasticsearch.common.component.LifecycleComponent;
-import org.elasticsearch.common.inject.Module;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.DiscoveryModule;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.discovery.gce.GceUnicastHostsProvider;
 import org.elasticsearch.discovery.zen.UnicastHostsProvider;
 import org.elasticsearch.discovery.zen.ZenDiscovery;
-import org.elasticsearch.discovery.zen.ZenPing;
 import org.elasticsearch.plugins.DiscoveryPlugin;
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -53,11 +50,7 @@ import org.elasticsearch.transport.TransportService;
 
 import java.io.Closeable;
 import java.io.IOException;
-import java.security.AccessController;
-import java.security.PrivilegedAction;
-import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -92,10 +85,12 @@ public class GceDiscoveryPlugin extends Plugin implements DiscoveryPlugin, Close
     @Override
     public Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                               NamedWriteableRegistry namedWriteableRegistry,
-                                                              ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                              MasterService masterService, ClusterApplier clusterApplier,
+                                                              ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
         // this is for backcompat with pre 5.1, where users would set discovery.type to use ec2 hosts provider
         return Collections.singletonMap(GCE, () ->
-            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider));
+            new ZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, masterService, clusterApplier,
+                clusterSettings, hostsProvider));
     }
 
     @Override

rest-api-spec/src/main/resources/rest-api-spec/test/cat.aliases/10_basic.yaml

@@ -126,6 +126,52 @@
   - match:
       $body: / (^|\n)test_2 .+ \n/
 
+---
+"Multiple alias names":
+
+  - skip:
+      version: " - 5.99.99"
+      reason:  multiple aliases are supported only from 6.0.0 on
+
+  - do:
+        indices.create:
+            index: test
+
+  - do:
+        indices.create:
+            index: test2
+  - do:
+        indices.create:
+            index: test3
+
+  - do:
+        indices.put_alias:
+            index: test
+            name: foo
+
+  - do:
+        indices.put_alias:
+            index: test2
+            name: bar
+  - do:
+        indices.put_alias:
+            index: test3
+            name: baz
+
+  - do:
+        cat.aliases:
+            name: foo,bar
+            v: true
+            h: [alias, index]
+            s: [index]
+
+  - match:
+      $body: |
+               /^  alias \s+ index \n
+                   foo   \s+ test  \n
+                   bar   \s+ test2
+               $/
+
 ---
 "Column headers":
 

test/framework/src/main/java/org/elasticsearch/test/ClusterServiceUtils.java

@@ -18,82 +18,90 @@
  */
 package org.elasticsearch.test;
 
+import org.apache.logging.log4j.core.util.Throwables;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.Version;
+import org.elasticsearch.cluster.ClusterChangedEvent;
+import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
+import org.elasticsearch.cluster.ClusterStateTaskListener;
+import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.NodeConnectionsService;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.ClusterApplierService;
 import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.discovery.DiscoverySettings;
+import org.elasticsearch.discovery.Discovery.AckListener;
 import org.elasticsearch.threadpool.ThreadPool;
 
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BiConsumer;
 
 import static junit.framework.TestCase.fail;
 
 public class ClusterServiceUtils {
 
-    public static ClusterService createClusterService(ThreadPool threadPool) {
+    public static MasterService createMasterService(ThreadPool threadPool, ClusterState initialClusterState) {
-        DiscoveryNode discoveryNode = new DiscoveryNode("node", ESTestCase.buildNewFakeTransportAddress(), Collections.emptyMap(),
+        MasterService masterService = new MasterService(Settings.EMPTY, threadPool);
-                EnumSet.allOf(DiscoveryNode.Role.class), Version.CURRENT);
+        AtomicReference<ClusterState> clusterStateRef = new AtomicReference<>(initialClusterState);
-        return createClusterService(threadPool, discoveryNode);
+        masterService.setClusterStatePublisher((event, ackListener) -> clusterStateRef.set(event.state()));
+        masterService.setClusterStateSupplier(clusterStateRef::get);
+        masterService.start();
+        return masterService;
     }
 
-    public static ClusterService createClusterService(ThreadPool threadPool, DiscoveryNode localNode) {
+    public static MasterService createMasterService(ThreadPool threadPool, DiscoveryNode localNode) {
-        return createClusterService(Settings.EMPTY, threadPool, localNode);
+        ClusterState initialClusterState = ClusterState.builder(new ClusterName(ClusterServiceUtils.class.getSimpleName()))
+            .nodes(DiscoveryNodes.builder()
+                .add(localNode)
+                .localNodeId(localNode.getId())
+                .masterNodeId(localNode.getId()))
+            .blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).build();
+        return createMasterService(threadPool, initialClusterState);
     }
 
-    public static ClusterService createClusterService(Settings settings, ThreadPool threadPool, DiscoveryNode localNode) {
+    public static void setState(ClusterApplierService executor, ClusterState clusterState) {
-        ClusterService clusterService = new ClusterService(
-            Settings.builder().put("cluster.name", "ClusterServiceTests").put(settings).build(),
-                new ClusterSettings(settings, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
-                threadPool, () -> localNode);
-        clusterService.setNodeConnectionsService(new NodeConnectionsService(Settings.EMPTY, null, null) {
-            @Override
-            public void connectToNodes(DiscoveryNodes discoveryNodes) {
-                // skip
-            }
-
-            @Override
-            public void disconnectFromNodesExcept(DiscoveryNodes nodesToKeep) {
-                // skip
-            }
-        });
-        clusterService.setClusterStatePublisher((event, ackListener) -> {
-        });
-        clusterService.setDiscoverySettings(new DiscoverySettings(Settings.EMPTY,
-            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS)));
-        clusterService.start();
-        final DiscoveryNodes.Builder nodes = DiscoveryNodes.builder(clusterService.state().nodes());
-        nodes.masterNodeId(clusterService.localNode().getId());
-        setState(clusterService, ClusterState.builder(clusterService.state()).nodes(nodes));
-        return clusterService;
-    }
-
-    public static ClusterService createClusterService(ClusterState initialState, ThreadPool threadPool) {
-        ClusterService clusterService = createClusterService(threadPool);
-        setState(clusterService, initialState);
-        return clusterService;
-    }
-
-    public static void setState(ClusterService clusterService, ClusterState.Builder clusterStateBuilder) {
-        setState(clusterService, clusterStateBuilder.build());
-    }
-
-    public static void setState(ClusterService clusterService, ClusterState clusterState) {
         CountDownLatch latch = new CountDownLatch(1);
-        clusterService.submitStateUpdateTask("test setting state", new LocalClusterUpdateTask() {
+        AtomicReference<Exception> exception = new AtomicReference<>();
+        executor.onNewClusterState("test setting state",
+            () -> ClusterState.builder(clusterState).version(clusterState.version() + 1).build(), new ClusterStateTaskListener() {
                 @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
+                public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                    latch.countDown();
+                }
+
+                @Override
+                public void onFailure(String source, Exception e) {
+                    exception.set(e);
+                    latch.countDown();
+                }
+            });
+        try {
+            latch.await();
+            if (exception.get() != null) {
+                Throwables.rethrow(exception.get());
+            }
+        } catch (InterruptedException e) {
+            throw new ElasticsearchException("unexpected exception", e);
+        }
+    }
+
+    public static void setState(MasterService executor, ClusterState clusterState) {
+        CountDownLatch latch = new CountDownLatch(1);
+        executor.submitStateUpdateTask("test setting state", new ClusterStateUpdateTask() {
+            @Override
+            public ClusterState execute(ClusterState currentState) throws Exception {
                 // make sure we increment versions as listener may depend on it for change
-                return newState(ClusterState.builder(clusterState).version(currentState.version() + 1).build());
+                return ClusterState.builder(clusterState).build();
             }
 
             @Override
@@ -112,4 +120,88 @@ public class ClusterServiceUtils {
             throw new ElasticsearchException("unexpected interruption", e);
         }
     }
+
+    public static ClusterService createClusterService(ThreadPool threadPool) {
+        DiscoveryNode discoveryNode = new DiscoveryNode("node", ESTestCase.buildNewFakeTransportAddress(), Collections.emptyMap(),
+                EnumSet.allOf(DiscoveryNode.Role.class), Version.CURRENT);
+        return createClusterService(threadPool, discoveryNode);
+    }
+
+    public static ClusterService createClusterService(ThreadPool threadPool, DiscoveryNode localNode) {
+        return createClusterService(threadPool, localNode, new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS));
+    }
+
+    public static ClusterService createClusterService(ThreadPool threadPool, DiscoveryNode localNode, ClusterSettings clusterSettings) {
+        ClusterService clusterService = new ClusterService(Settings.builder().put("cluster.name", "ClusterServiceTests").build(),
+            clusterSettings, threadPool);
+        clusterService.setNodeConnectionsService(new NodeConnectionsService(Settings.EMPTY, null, null) {
+            @Override
+            public void connectToNodes(DiscoveryNodes discoveryNodes) {
+                // skip
+            }
+
+            @Override
+            public void disconnectFromNodesExcept(DiscoveryNodes nodesToKeep) {
+                // skip
+            }
+        });
+        ClusterState initialClusterState = ClusterState.builder(new ClusterName(ClusterServiceUtils.class.getSimpleName()))
+            .nodes(DiscoveryNodes.builder()
+                .add(localNode)
+                .localNodeId(localNode.getId())
+                .masterNodeId(localNode.getId()))
+            .blocks(ClusterBlocks.EMPTY_CLUSTER_BLOCK).build();
+        clusterService.getClusterApplierService().setInitialState(initialClusterState);
+        clusterService.getMasterService().setClusterStatePublisher(
+            createClusterStatePublisher(clusterService.getClusterApplierService()));
+        clusterService.getMasterService().setClusterStateSupplier(clusterService.getClusterApplierService()::state);
+        clusterService.start();
+        return clusterService;
+    }
+
+    public static BiConsumer<ClusterChangedEvent, AckListener> createClusterStatePublisher(ClusterApplier clusterApplier) {
+        return (event, ackListener) -> {
+            CountDownLatch latch = new CountDownLatch(1);
+            AtomicReference<Exception> ex = new AtomicReference<>();
+            clusterApplier.onNewClusterState("mock_publish_to_self[" + event.source() + "]", () -> event.state(),
+                new ClusterStateTaskListener() {
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        latch.countDown();
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        ex.set(e);
+                        latch.countDown();
+                    }
+                }
+            );
+            try {
+                latch.await();
+            } catch (InterruptedException e) {
+                Throwables.rethrow(e);
+            }
+            if (ex.get() != null) {
+                Throwables.rethrow(ex.get());
+            }
+        };
+    }
+
+    public static ClusterService createClusterService(ClusterState initialState, ThreadPool threadPool) {
+        ClusterService clusterService = createClusterService(threadPool);
+        setState(clusterService, initialState);
+        return clusterService;
+    }
+
+    public static void setState(ClusterService clusterService, ClusterState.Builder clusterStateBuilder) {
+        setState(clusterService, clusterStateBuilder.build());
+    }
+
+    /**
+     * Sets the state on the cluster applier service
+     */
+    public static void setState(ClusterService clusterService, ClusterState clusterState) {
+        setState(clusterService.getClusterApplierService(), clusterState);
+    }
 }

test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java

@@ -570,7 +570,8 @@ public abstract class ESIntegTestCase extends ESTestCase {
                                 final ZenDiscovery zenDiscovery = (ZenDiscovery) discovery;
                                 assertBusy(() -> {
                                     final ClusterState[] states = zenDiscovery.pendingClusterStates();
-                                    assertThat(zenDiscovery.localNode().getName() + " still having pending states:\n" +
+                                    assertThat(zenDiscovery.clusterState().nodes().getLocalNode().getName() +
+                                            " still having pending states:\n" +
                                             Stream.of(states).map(ClusterState::toString).collect(Collectors.joining("\n")),
                                         states, emptyArray());
                                 });

test/framework/src/main/java/org/elasticsearch/test/discovery/TestZenDiscovery.java

@@ -24,8 +24,10 @@ import java.util.List;
 import java.util.Map;
 import java.util.function.Supplier;
 
-import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.ClusterApplier;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.Discovery;
@@ -56,9 +58,11 @@ public class TestZenDiscovery extends ZenDiscovery {
         @Override
         public Map<String, Supplier<Discovery>> getDiscoveryTypes(ThreadPool threadPool, TransportService transportService,
                                                                   NamedWriteableRegistry namedWriteableRegistry,
-                                                                  ClusterService clusterService, UnicastHostsProvider hostsProvider) {
+                                                                  MasterService masterService, ClusterApplier clusterApplier,
+                                                                  ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
             return Collections.singletonMap("test-zen",
-                () -> new TestZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider));
+                () -> new TestZenDiscovery(settings, threadPool, transportService, namedWriteableRegistry, masterService,
+                    clusterApplier, clusterSettings, hostsProvider));
         }
 
         @Override
@@ -73,9 +77,10 @@ public class TestZenDiscovery extends ZenDiscovery {
     }
 
     private TestZenDiscovery(Settings settings, ThreadPool threadPool, TransportService transportService,
-                             NamedWriteableRegistry namedWriteableRegistry, ClusterService clusterService,
+                             NamedWriteableRegistry namedWriteableRegistry, MasterService masterService,
-                             UnicastHostsProvider hostsProvider) {
+                             ClusterApplier clusterApplier, ClusterSettings clusterSettings, UnicastHostsProvider hostsProvider) {
-        super(settings, threadPool, transportService, namedWriteableRegistry, clusterService, hostsProvider);
+        super(settings, threadPool, transportService, namedWriteableRegistry, masterService, clusterApplier, clusterSettings,
+            hostsProvider);
     }
 
     @Override

test/framework/src/main/java/org/elasticsearch/test/disruption/BlockClusterStateProcessing.java

@@ -18,8 +18,7 @@
  */
 package org.elasticsearch.test.disruption;
 
-import org.elasticsearch.cluster.ClusterState;
+import org.apache.logging.log4j.core.util.Throwables;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.unit.TimeValue;
@@ -58,23 +57,19 @@ public class BlockClusterStateProcessing extends SingleNodeDisruption {
         boolean success = disruptionLatch.compareAndSet(null, new CountDownLatch(1));
         assert success : "startDisrupting called without waiting on stopDisrupting to complete";
         final CountDownLatch started = new CountDownLatch(1);
-        clusterService.submitStateUpdateTask("service_disruption_block", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+        clusterService.getClusterApplierService().runOnApplierThread("service_disruption_block",
-
+            currentState -> {
-            @Override
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
                 started.countDown();
                 CountDownLatch latch = disruptionLatch.get();
                 if (latch != null) {
+                    try {
                         latch.await();
+                    } catch (InterruptedException e) {
+                        Throwables.rethrow(e);
                     }
-                return unchanged();
                 }
-
+            }, (source, e) -> logger.error("unexpected error during disruption", e),
-            @Override
+            Priority.IMMEDIATE);
-            public void onFailure(String source, Exception e) {
-                logger.error("unexpected error during disruption", e);
-            }
-        });
         try {
             started.await();
         } catch (InterruptedException e) {

test/framework/src/main/java/org/elasticsearch/test/disruption/SlowClusterStateProcessing.java

@@ -18,8 +18,7 @@
  */
 package org.elasticsearch.test.disruption;
 
-import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.ExceptionsHelper;
-import org.elasticsearch.cluster.LocalClusterUpdateTask;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.unit.TimeValue;
@@ -102,10 +101,9 @@ public class SlowClusterStateProcessing extends SingleNodeDisruption {
             return false;
         }
         final AtomicBoolean stopped = new AtomicBoolean(false);
-        clusterService.submitStateUpdateTask("service_disruption_delay", new LocalClusterUpdateTask(Priority.IMMEDIATE) {
+        clusterService.getClusterApplierService().runOnApplierThread("service_disruption_delay",
-
+            currentState -> {
-            @Override
+                try {
-            public ClusterTasksResult<LocalClusterUpdateTask> execute(ClusterState currentState) throws Exception {
                     long count = duration.millis() / 200;
                     // wait while checking for a stopped
                     for (; count > 0 && !stopped.get(); count--) {
@@ -115,14 +113,11 @@ public class SlowClusterStateProcessing extends SingleNodeDisruption {
                         Thread.sleep(duration.millis() % 200);
                     }
                     countDownLatch.countDown();
-                return unchanged();
+                } catch (InterruptedException e) {
+                    ExceptionsHelper.reThrowIfNotNull(e);
                 }
-
+            }, (source, e) -> countDownLatch.countDown(),
-            @Override
+            Priority.IMMEDIATE);
-            public void onFailure(String source, Exception e) {
-                countDownLatch.countDown();
-            }
-        });
         try {
             countDownLatch.await();
         } catch (InterruptedException e) {