Add validation for supported index version on node join, restore, upgrade & open index (#21830)

Today we can easily join a cluster that holds an index we don't support since
we currently allow rolling upgrades from 5.x to 6.x. Along the same lines we don't check if we can support an index based on the nodes in the cluster when we open, restore or metadata-upgrade and index. This commit adds
additional safety that fails cluster state validation, open, restore and /or upgrade if there is an open index with an incompatible index version created in the cluster.

Realtes to #21670

core/src/main/java/org/elasticsearch/Version.java

@@ -218,12 +218,17 @@ public class Version {
     }
 
     /**
-     * Returns the smallest version between the 2.
+     * Returns the minimum version between the 2.
      */
-    public static Version smallest(Version version1, Version version2) {
+    public static Version min(Version version1, Version version2) {
         return version1.id < version2.id ? version1 : version2;
     }
 
+    /**
+     * Returns the maximum version between the 2
+     */
+    public static Version max(Version version1, Version version2) { return version1.id > version2.id ? version1 : version2; }
+
     /**
      * Returns the version given its string representation, current version if the argument is null or empty
      */
@@ -326,7 +331,22 @@ public class Version {
             bwcMajor = major;
             bwcMinor = 0;
         }
-        return Version.smallest(this, fromId(bwcMajor * 1000000 + bwcMinor * 10000 + 99));
+        return Version.min(this, fromId(bwcMajor * 1000000 + bwcMinor * 10000 + 99));
+    }
+
+    /**
+     * Returns the minimum created index version that this version supports. Indices created with lower versions
+     * can't be used with this version.
+     */
+    public Version minimumIndexCompatibilityVersion() {
+        final int bwcMajor;
+        if (major == 5) {
+            bwcMajor = 2; // we jumped from 2 to 5
+        } else {
+            bwcMajor = major - 1;
+        }
+        final int bwcMinor = 0;
+        return Version.min(this, fromId(bwcMajor * 1000000 + bwcMinor * 10000 + 99));
     }
 
     /**
@@ -414,5 +434,4 @@ public class Version {
     public boolean isRelease() {
         return build == 99;
     }
-
 }

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataCreateIndexService.java

@@ -316,7 +316,7 @@ public class MetaDataCreateIndexService extends AbstractComponent {
 
                             if (indexSettingsBuilder.get(SETTING_VERSION_CREATED) == null) {
                                 DiscoveryNodes nodes = currentState.nodes();
-                                final Version createdVersion = Version.smallest(Version.CURRENT, nodes.getSmallestNonClientNodeVersion());
+                                final Version createdVersion = Version.min(Version.CURRENT, nodes.getSmallestNonClientNodeVersion());
                                 indexSettingsBuilder.put(SETTING_VERSION_CREATED, createdVersion);
                             }
 

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexStateService.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.admin.indices.close.CloseIndexClusterStateUpdateRequest;
 import org.elasticsearch.action.admin.indices.open.OpenIndexClusterStateUpdateRequest;
@@ -160,12 +161,14 @@ public class MetaDataIndexStateService extends AbstractComponent {
                 MetaData.Builder mdBuilder = MetaData.builder(currentState.metaData());
                 ClusterBlocks.Builder blocksBuilder = ClusterBlocks.builder()
                         .blocks(currentState.blocks());
+                final Version minIndexCompatibilityVersion = currentState.getNodes().getMaxNodeVersion()
+                    .minimumIndexCompatibilityVersion();
                 for (IndexMetaData closedMetaData : indicesToOpen) {
                     final String indexName = closedMetaData.getIndex().getName();
                     IndexMetaData indexMetaData = IndexMetaData.builder(closedMetaData).state(IndexMetaData.State.OPEN).build();
                     // The index might be closed because we couldn't import it due to old incompatible version
                     // We need to check that this index can be upgraded to the current version
-                    indexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData);
+                    indexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData, minIndexCompatibilityVersion);
                     try {
                         indicesService.verifyIndexMetadata(indexMetaData, indexMetaData);
                     } catch (Exception e) {

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java

@@ -67,13 +67,13 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
      * If the index does not need upgrade it returns the index metadata unchanged, otherwise it returns a modified index metadata. If index
      * cannot be updated the method throws an exception.
      */
-    public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData) {
+    public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData, Version minimumIndexCompatibilityVersion) {
         // Throws an exception if there are too-old segments:
         if (isUpgraded(indexMetaData)) {
             assert indexMetaData == archiveBrokenIndexSettings(indexMetaData) : "all settings must have been upgraded before";
             return indexMetaData;
         }
-        checkSupportedVersion(indexMetaData);
+        checkSupportedVersion(indexMetaData, minimumIndexCompatibilityVersion);
         IndexMetaData newMetaData = indexMetaData;
         // we have to run this first otherwise in we try to create IndexSettings
         // with broken settings and fail in checkMappingsCompatibility
@@ -92,21 +92,26 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
     }
 
     /**
-     * Elasticsearch 5.0 no longer supports indices with pre Lucene v5.0 (Elasticsearch v2.0.0.beta1) segments. All indices
+     * Elasticsearch v6.0 no longer supports indices created pre v5.0. All indices
-     * that were created before Elasticsearch v2.0.0.beta1 should be reindexed in Elasticsearch 2.x
+     * that were created before Elasticsearch v5.0 should be re-indexed in Elasticsearch 5.x
-     * before they can be opened by this version of elasticsearch.     */
+     * before they can be opened by this version of elasticsearch.
-    private void checkSupportedVersion(IndexMetaData indexMetaData) {
+     */
-        if (indexMetaData.getState() == IndexMetaData.State.OPEN && isSupportedVersion(indexMetaData) == false) {
+    private void checkSupportedVersion(IndexMetaData indexMetaData, Version minimumIndexCompatibilityVersion) {
-            throw new IllegalStateException("The index [" + indexMetaData.getIndex() + "] was created before v2.0.0.beta1."
+        if (indexMetaData.getState() == IndexMetaData.State.OPEN && isSupportedVersion(indexMetaData,
-                    + " It should be reindexed in Elasticsearch 2.x before upgrading to " + Version.CURRENT + ".");
+            minimumIndexCompatibilityVersion) == false) {
+            throw new IllegalStateException("The index [" + indexMetaData.getIndex() + "] was created with version ["
+                + indexMetaData.getCreationVersion() + "] but the minimum compatible version is ["
+
+                + minimumIndexCompatibilityVersion + "]. It should be re-indexed in Elasticsearch " + minimumIndexCompatibilityVersion.major
+                + ".x before upgrading to " + Version.CURRENT + ".");
         }
     }
 
     /*
      * Returns true if this index can be supported by the current version of elasticsearch
      */
-    private static boolean isSupportedVersion(IndexMetaData indexMetaData) {
+    private static boolean isSupportedVersion(IndexMetaData indexMetaData, Version minimumIndexCompatibilityVersion) {
-        return indexMetaData.getCreationVersion().onOrAfter(Version.V_5_0_0_beta1);
+        return indexMetaData.getCreationVersion().onOrAfter(minimumIndexCompatibilityVersion);
     }
 
     /**
@@ -173,4 +178,4 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
             return indexMetaData;
         }
     }
-}
+}

core/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java

@@ -56,10 +56,13 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
     private final String masterNodeId;
     private final String localNodeId;
     private final Version minNonClientNodeVersion;
+    private final Version maxNodeVersion;
+    private final Version minNodeVersion;
 
     private DiscoveryNodes(ImmutableOpenMap<String, DiscoveryNode> nodes, ImmutableOpenMap<String, DiscoveryNode> dataNodes,
                            ImmutableOpenMap<String, DiscoveryNode> masterNodes, ImmutableOpenMap<String, DiscoveryNode> ingestNodes,
-                           String masterNodeId, String localNodeId, Version minNonClientNodeVersion) {
+                           String masterNodeId, String localNodeId, Version minNonClientNodeVersion, Version maxNodeVersion,
+                           Version minNodeVersion) {
         this.nodes = nodes;
         this.dataNodes = dataNodes;
         this.masterNodes = masterNodes;
@@ -67,6 +70,8 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
         this.masterNodeId = masterNodeId;
         this.localNodeId = localNodeId;
         this.minNonClientNodeVersion = minNonClientNodeVersion;
+        this.minNodeVersion = minNodeVersion;
+        this.maxNodeVersion = maxNodeVersion;
     }
 
     @Override
@@ -235,6 +240,24 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
         return minNonClientNodeVersion;
     }
 
+    /**
+     * Returns the version of the node with the oldest version in the cluster.
+     *
+     * @return the oldest version in the cluster
+     */
+    public Version getMinNodeVersion() {
+        return minNodeVersion;
+    }
+
+    /**
+     * Returns the version of the node with the yougest version in the cluster
+     *
+     * @return the oldest version in the cluster
+     */
+    public Version getMaxNodeVersion() {
+        return maxNodeVersion;
+    }
+
     /**
      * Resolve a node with a given id
      *
@@ -631,25 +654,27 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
             ImmutableOpenMap.Builder<String, DiscoveryNode> masterNodesBuilder = ImmutableOpenMap.builder();
             ImmutableOpenMap.Builder<String, DiscoveryNode> ingestNodesBuilder = ImmutableOpenMap.builder();
             Version minNodeVersion = Version.CURRENT;
+            Version maxNodeVersion = Version.CURRENT;
             Version minNonClientNodeVersion = Version.CURRENT;
             for (ObjectObjectCursor<String, DiscoveryNode> nodeEntry : nodes) {
                 if (nodeEntry.value.isDataNode()) {
                     dataNodesBuilder.put(nodeEntry.key, nodeEntry.value);
-                    minNonClientNodeVersion = Version.smallest(minNonClientNodeVersion, nodeEntry.value.getVersion());
+                    minNonClientNodeVersion = Version.min(minNonClientNodeVersion, nodeEntry.value.getVersion());
                 }
                 if (nodeEntry.value.isMasterNode()) {
                     masterNodesBuilder.put(nodeEntry.key, nodeEntry.value);
-                    minNonClientNodeVersion = Version.smallest(minNonClientNodeVersion, nodeEntry.value.getVersion());
+                    minNonClientNodeVersion = Version.min(minNonClientNodeVersion, nodeEntry.value.getVersion());
                 }
                 if (nodeEntry.value.isIngestNode()) {
                     ingestNodesBuilder.put(nodeEntry.key, nodeEntry.value);
                 }
-                minNodeVersion = Version.smallest(minNodeVersion, nodeEntry.value.getVersion());
+                minNodeVersion = Version.min(minNodeVersion, nodeEntry.value.getVersion());
+                maxNodeVersion = Version.max(maxNodeVersion, nodeEntry.value.getVersion());
             }
 
             return new DiscoveryNodes(
                 nodes.build(), dataNodesBuilder.build(), masterNodesBuilder.build(), ingestNodesBuilder.build(),
-                masterNodeId, localNodeId, minNonClientNodeVersion
+                masterNodeId, localNodeId, minNonClientNodeVersion, maxNodeVersion, minNodeVersion
             );
         }
 

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

@@ -19,14 +19,16 @@
 
 package org.elasticsearch.discovery.zen;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
-import org.elasticsearch.discovery.zen.DiscoveryNodesProvider;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.EmptyTransportResponseHandler;
 import org.elasticsearch.transport.TransportChannel;
@@ -37,6 +39,7 @@ import org.elasticsearch.transport.TransportService;
 
 import java.io.IOException;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Supplier;
 
 public class MembershipAction extends AbstractComponent {
 
@@ -58,21 +61,20 @@ public class MembershipAction extends AbstractComponent {
 
     private final TransportService transportService;
 
-    private final DiscoveryNodesProvider nodesProvider;
-
     private final MembershipListener listener;
 
     public MembershipAction(Settings settings, TransportService transportService,
-                            DiscoveryNodesProvider nodesProvider, MembershipListener listener) {
+                            Supplier<DiscoveryNode> localNodeSupplier, MembershipListener listener) {
         super(settings);
         this.transportService = transportService;
-        this.nodesProvider = nodesProvider;
         this.listener = listener;
 
+
         transportService.registerRequestHandler(DISCOVERY_JOIN_ACTION_NAME, JoinRequest::new,
             ThreadPool.Names.GENERIC, new JoinRequestRequestHandler());
-        transportService.registerRequestHandler(DISCOVERY_JOIN_VALIDATE_ACTION_NAME, ValidateJoinRequest::new,
+        transportService.registerRequestHandler(DISCOVERY_JOIN_VALIDATE_ACTION_NAME,
-            ThreadPool.Names.GENERIC, new ValidateJoinRequestRequestHandler());
+            () -> new ValidateJoinRequest(localNodeSupplier), ThreadPool.Names.GENERIC,
+            new ValidateJoinRequestRequestHandler());
         transportService.registerRequestHandler(DISCOVERY_LEAVE_ACTION_NAME, LeaveRequest::new,
             ThreadPool.Names.GENERIC, new LeaveRequestRequestHandler());
     }
@@ -152,20 +154,23 @@ public class MembershipAction extends AbstractComponent {
         }
     }
 
-    class ValidateJoinRequest extends TransportRequest {
+    static class ValidateJoinRequest extends TransportRequest {
+        private final Supplier<DiscoveryNode> localNode;
         private ClusterState state;
 
-        ValidateJoinRequest() {
+        ValidateJoinRequest(Supplier<DiscoveryNode> localNode) {
+            this.localNode = localNode;
         }
 
         ValidateJoinRequest(ClusterState state) {
             this.state = state;
+            this.localNode = state.nodes()::getLocalNode;
         }
 
         @Override
         public void readFrom(StreamInput in) throws IOException {
             super.readFrom(in);
-            this.state = ClusterState.Builder.readFrom(in, nodesProvider.nodes().getLocalNode());
+            this.state = ClusterState.Builder.readFrom(in, localNode.get());
         }
 
         @Override
@@ -175,15 +180,31 @@ public class MembershipAction extends AbstractComponent {
         }
     }
 
-    class ValidateJoinRequestRequestHandler implements TransportRequestHandler<ValidateJoinRequest> {
+    static class ValidateJoinRequestRequestHandler implements TransportRequestHandler<ValidateJoinRequest> {
 
         @Override
         public void messageReceived(ValidateJoinRequest request, TransportChannel channel) throws Exception {
+            ensureIndexCompatibility(Version.CURRENT.minimumIndexCompatibilityVersion(), request.state.getMetaData());
             // for now, the mere fact that we can serialize the cluster state acts as validation....
             channel.sendResponse(TransportResponse.Empty.INSTANCE);
         }
     }
 
+    /**
+     * Ensures that all indices are compatible with the supported index version.
+     * @throws IllegalStateException if any index is incompatible with the given version
+     */
+    static void ensureIndexCompatibility(final Version supportedIndexVersion, MetaData metaData) {
+        // we ensure that all indices in the cluster we join are compatible with us no matter if they are
+        // closed or not we can't read mappings of these indices so we need to reject the join...
+        for (IndexMetaData idxMetaData : metaData) {
+            if (idxMetaData.getCreationVersion().before(supportedIndexVersion)) {
+                throw new IllegalStateException("index " + idxMetaData.getIndex() + " version not supported: "
+                    + idxMetaData.getCreationVersion() + " minimum compatible index version is: " + supportedIndexVersion);
+            }
+        }
+    }
+
     public static class LeaveRequest extends TransportRequest {
 
         private DiscoveryNode node;

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

@@ -410,7 +410,6 @@ public class NodeJoinController extends AbstractComponent {
         @Override
         public BatchResult<DiscoveryNode> execute(ClusterState currentState, List<DiscoveryNode> joiningNodes) throws Exception {
             final BatchResult.Builder<DiscoveryNode> results = BatchResult.builder();
-
             final DiscoveryNodes currentNodes = currentState.nodes();
             boolean nodesChanged = false;
             ClusterState.Builder newState;
@@ -435,8 +434,10 @@ public class NodeJoinController extends AbstractComponent {
 
             assert nodesBuilder.isLocalNodeElectedMaster();
 
+            Version minNodeVersion = Version.CURRENT;
             // processing any joins
             for (final DiscoveryNode node : joiningNodes) {
+                minNodeVersion = Version.min(minNodeVersion, node.getVersion());
                 if (node.equals(BECOME_MASTER_TASK) || node.equals(FINISH_ELECTION_TASK)) {
                     // noop
                 } else if (currentNodes.nodeExists(node)) {
@@ -452,7 +453,9 @@ public class NodeJoinController extends AbstractComponent {
                 }
                 results.success(node);
             }
-
+            // we do this validation quite late to prevent race conditions between nodes joining and importing dangling indices
+            // we have to reject nodes that don't support all indices we have in this cluster
+            MembershipAction.ensureIndexCompatibility(minNodeVersion.minimumIndexCompatibilityVersion(), currentState.getMetaData());
             if (nodesChanged) {
                 newState.nodes(nodesBuilder);
                 return results.build(allocationService.reroute(newState.build(), "node_join"));

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

@@ -183,7 +183,7 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
                         new NewPendingClusterStateListener(),
                         discoverySettings,
                         clusterService.getClusterName());
-        this.membership = new MembershipAction(settings, transportService, this, new MembershipListener());
+        this.membership = new MembershipAction(settings, transportService, this::localNode, new MembershipListener());
         this.joinThreadControl = new JoinThreadControl(threadPool);
 
         transportService.registerRequestHandler(
@@ -301,7 +301,6 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         if (!clusterChangedEvent.state().getNodes().isLocalNodeElectedMaster()) {
             throw new IllegalStateException("Shouldn't publish state when not master");
         }
-
         try {
             publishClusterState.publish(clusterChangedEvent, electMaster.minimumMasterNodes(), ackListener);
         } catch (FailedToCommitClusterStateException t) {
@@ -852,6 +851,9 @@ public class ZenDiscovery extends AbstractLifecycleComponent implements Discover
         if (nodeJoinController == null) {
             throw new IllegalStateException("discovery module is not yet started");
         } else {
+            // we do this in a couple of places including the cluster update thread. This one here is really just best effort
+            // to ensure we fail as fast as possible.
+            MembershipAction.ensureIndexCompatibility(node.getVersion().minimumIndexCompatibilityVersion(), state.getMetaData());
             // try and connect to the node, if it fails, we can raise an exception back to the client...
             transportService.connectToNode(node);
 

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

@@ -245,7 +245,8 @@ public class GatewayMetaState extends AbstractComponent implements ClusterStateL
         boolean changed = false;
         final MetaData.Builder upgradedMetaData = MetaData.builder(metaData);
         for (IndexMetaData indexMetaData : metaData) {
-            IndexMetaData newMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData);
+            IndexMetaData newMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData,
+                Version.CURRENT.minimumIndexCompatibilityVersion());
             changed |= indexMetaData != newMetaData;
             upgradedMetaData.put(newMetaData, false);
         }

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

@@ -21,6 +21,7 @@ package org.elasticsearch.gateway;
 
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.apache.logging.log4j.util.Supplier;
+import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.block.ClusterBlocks;
@@ -28,6 +29,7 @@ import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.metadata.MetaDataIndexUpgradeService;
 import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.RoutingTable;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
 import org.elasticsearch.cluster.service.ClusterService;
@@ -126,10 +128,18 @@ public class LocalAllocateDangledIndices extends AbstractComponent {
                     MetaData.Builder metaData = MetaData.builder(currentState.metaData());
                     ClusterBlocks.Builder blocks = ClusterBlocks.builder().blocks(currentState.blocks());
                     RoutingTable.Builder routingTableBuilder = RoutingTable.builder(currentState.routingTable());
-
+                    final Version minIndexCompatibilityVersion = currentState.getNodes().getMaxNodeVersion()
+                        .minimumIndexCompatibilityVersion();
                     boolean importNeeded = false;
                     StringBuilder sb = new StringBuilder();
                     for (IndexMetaData indexMetaData : request.indices) {
+                        if (indexMetaData.getCreationVersion().before(minIndexCompatibilityVersion)) {
+                            logger.warn("ignoring dangled index [{}] on node [{}]" +
+                                " since it's created version [{}] is not supported by at least one node in the cluster minVersion [{}]",
+                                indexMetaData.getIndex(), request.fromNode, indexMetaData.getCreationVersion(),
+                                minIndexCompatibilityVersion);
+                            continue;
+                        }
                         if (currentState.metaData().hasIndex(indexMetaData.getIndex().getName())) {
                             continue;
                         }
@@ -144,7 +154,8 @@ public class LocalAllocateDangledIndices extends AbstractComponent {
                         try {
                             // The dangled index might be from an older version, we need to make sure it's compatible
                             // with the current version and upgrade it if needed.
-                            upgradedIndexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData);
+                            upgradedIndexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData,
+                                minIndexCompatibilityVersion);
                         } catch (Exception ex) {
                             // upgrade failed - adding index as closed
                             logger.warn((Supplier<?>) () -> new ParameterizedMessage("found dangled index [{}] on node [{}]. This index cannot be upgraded to the latest version, adding as closed", indexMetaData.getIndex(), request.fromNode), ex);

core/src/main/java/org/elasticsearch/snapshots/RestoreService.java

@@ -83,6 +83,7 @@ import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import static java.util.Collections.min;
 import static java.util.Collections.unmodifiableSet;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_AUTO_EXPAND_REPLICAS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_CREATION_DATE;
@@ -225,6 +226,8 @@ public class RestoreService extends AbstractComponent implements ClusterStateLis
                     if (!renamedIndices.isEmpty()) {
                         // We have some indices to restore
                         ImmutableOpenMap.Builder<ShardId, RestoreInProgress.ShardRestoreStatus> shardsBuilder = ImmutableOpenMap.builder();
+                        final Version minIndexCompatibilityVersion = currentState.getNodes().getMaxNodeVersion()
+                            .minimumIndexCompatibilityVersion();
                         for (Map.Entry<String, String> indexEntry : renamedIndices.entrySet()) {
                             String index = indexEntry.getValue();
                             boolean partial = checkPartial(index);
@@ -233,7 +236,8 @@ public class RestoreService extends AbstractComponent implements ClusterStateLis
                             IndexMetaData snapshotIndexMetaData = metaData.index(index);
                             snapshotIndexMetaData = updateIndexSettings(snapshotIndexMetaData, request.indexSettings, request.ignoreIndexSettings);
                             try {
-                                snapshotIndexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(snapshotIndexMetaData);
+                                snapshotIndexMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(snapshotIndexMetaData,
+                                    minIndexCompatibilityVersion);
                             } catch (Exception ex) {
                                 throw new SnapshotRestoreException(snapshot, "cannot restore index [" + index + "] because it cannot be upgraded", ex);
                             }

core/src/main/java/org/elasticsearch/transport/TcpTransport.java

@@ -909,7 +909,7 @@ public abstract class TcpTransport<Channel> extends AbstractLifecycleComponent i
             // we pick the smallest of the 2, to support both backward and forward compatibility
             // note, this is the only place we need to do this, since from here on, we use the serialized version
             // as the version to use also when the node receiving this request will send the response with
-            Version version = Version.smallest(getCurrentVersion(), node.getVersion());
+            Version version = Version.min(getCurrentVersion(), node.getVersion());
 
             stream.setVersion(version);
             threadPool.getThreadContext().writeTo(stream);

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

@@ -64,7 +64,37 @@ public class VersionTests extends ESTestCase {
         assertTrue(Version.fromString("5.0.0").onOrAfter(Version.fromString("5.0.0-beta2")));
         assertTrue(Version.fromString("5.0.0-rc1").onOrAfter(Version.fromString("5.0.0-beta24")));
         assertTrue(Version.fromString("5.0.0-alpha24").before(Version.fromString("5.0.0-beta0")));
+    }
 
+    public void testMin() {
+        assertEquals(VersionUtils.getPreviousVersion(), Version.min(Version.CURRENT, VersionUtils.getPreviousVersion()));
+        assertEquals(Version.fromString("1.0.1"), Version.min(Version.fromString("1.0.1"), Version.CURRENT));
+        Version version = VersionUtils.randomVersion(random());
+        Version version1 = VersionUtils.randomVersion(random());
+        if (version.id <= version1.id) {
+            assertEquals(version, Version.min(version1, version));
+        } else {
+            assertEquals(version1, Version.min(version1, version));
+        }
+    }
+
+    public void testMax() {
+        assertEquals(Version.CURRENT, Version.max(Version.CURRENT, VersionUtils.getPreviousVersion()));
+        assertEquals(Version.CURRENT, Version.max(Version.fromString("1.0.1"), Version.CURRENT));
+        Version version = VersionUtils.randomVersion(random());
+        Version version1 = VersionUtils.randomVersion(random());
+        if (version.id >= version1.id) {
+            assertEquals(version, Version.max(version1, version));
+        } else {
+            assertEquals(version1, Version.max(version1, version));
+        }
+    }
+
+    public void testMinimumIndexCompatibilityVersion() {
+        assertEquals(Version.V_5_0_0, Version.V_6_0_0_alpha1_UNRELEASED.minimumIndexCompatibilityVersion());
+        assertEquals(Version.V_2_0_0, Version.V_5_0_0.minimumIndexCompatibilityVersion());
+        assertEquals(Version.V_2_0_0, Version.V_5_1_1_UNRELEASED.minimumIndexCompatibilityVersion());
+        assertEquals(Version.V_2_0_0, Version.V_5_0_0_alpha1.minimumIndexCompatibilityVersion());
     }
 
     public void testVersionConstantPresent() {

core/src/test/java/org/elasticsearch/bwcompat/OldIndexBackwardsCompatibilityIT.java

@@ -189,7 +189,7 @@ public class OldIndexBackwardsCompatibilityIT extends ESIntegTestCase {
         for (Version v : VersionUtils.allReleasedVersions()) {
             if (VersionUtils.isSnapshot(v)) continue;  // snapshots are unreleased, so there is no backcompat yet
             if (v.isRelease() == false) continue; // no guarantees for prereleases
-            if (v.before(Version.V_5_0_0)) continue; // we can only support one major version backward
+            if (v.before(Version.CURRENT.minimumIndexCompatibilityVersion())) continue; // we can only support one major version backward
             if (v.equals(Version.CURRENT)) continue; // the current version is always compatible with itself
             expectedVersions.add("index-" + v.toString() + ".zip");
         }

core/src/test/java/org/elasticsearch/bwcompat/RestoreBackwardsCompatIT.java

@@ -97,7 +97,7 @@ public class RestoreBackwardsCompatIT extends AbstractSnapshotIntegTestCase {
         for (Version v : VersionUtils.allReleasedVersions()) {
             if (VersionUtils.isSnapshot(v)) continue;  // snapshots are unreleased, so there is no backcompat yet
             if (v.isRelease() == false) continue; // no guarantees for prereleases
-            if (v.before(Version.V_5_0_0)) continue; // we only support versions N and N-1
+            if (v.before(Version.CURRENT.minimumIndexCompatibilityVersion())) continue; // we only support versions N and N-1
             if (v.equals(Version.CURRENT)) continue; // the current version is always compatible with itself
             expectedVersions.add(v.toString());
         }
@@ -206,7 +206,7 @@ public class RestoreBackwardsCompatIT extends AbstractSnapshotIntegTestCase {
         logger.info("--> restoring unsupported snapshot");
         try {
             client().admin().cluster().prepareRestoreSnapshot(repo, snapshot).setRestoreGlobalState(true).setWaitForCompletion(true).get();
-            fail("should have failed to restore");
+            fail("should have failed to restore - " + repo);
         } catch (SnapshotRestoreException ex) {
             assertThat(ex.getMessage(), containsString("cannot restore index"));
             assertThat(ex.getMessage(), containsString("because it cannot be upgraded"));

core/src/test/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeServiceTests.java

@@ -60,11 +60,11 @@ public class MetaDataIndexUpgradeServiceTests extends ESTestCase {
             Collections.emptyMap()), IndexScopedSettings.DEFAULT_SCOPED_SETTINGS);
         IndexMetaData src = newIndexMeta("foo", Settings.builder().put("index.refresh_interval", "-200").build());
         assertFalse(service.isUpgraded(src));
-        src = service.upgradeIndexMetaData(src);
+        src = service.upgradeIndexMetaData(src, Version.CURRENT.minimumIndexCompatibilityVersion());
         assertTrue(service.isUpgraded(src));
         assertEquals("-200", src.getSettings().get("archived.index.refresh_interval"));
         assertNull(src.getSettings().get("index.refresh_interval"));
-        assertSame(src, service.upgradeIndexMetaData(src)); // no double upgrade
+        assertSame(src, service.upgradeIndexMetaData(src, Version.CURRENT.minimumIndexCompatibilityVersion())); // no double upgrade
     }
 
     public void testIsUpgraded() {
@@ -87,16 +87,17 @@ public class MetaDataIndexUpgradeServiceTests extends ESTestCase {
             .put(IndexMetaData.SETTING_VERSION_CREATED, Version.fromString("2.4.0"))
             .put(IndexMetaData.SETTING_VERSION_MINIMUM_COMPATIBLE,
             Version.CURRENT.luceneVersion.toString()).build());
-        String message = expectThrows(IllegalStateException.class, () -> service.upgradeIndexMetaData(metaData)).getMessage();
+        String message = expectThrows(IllegalStateException.class, () -> service.upgradeIndexMetaData(metaData,
-        assertEquals(message, "The index [[foo/BOOM]] was created before v2.0.0.beta1. It should be reindexed in Elasticsearch 2.x " +
+            Version.CURRENT.minimumIndexCompatibilityVersion())).getMessage();
-            "before upgrading to " + Version.CURRENT.toString() + ".");
+        assertEquals(message, "The index [[foo/BOOM]] was created with version [2.4.0] but the minimum compatible version is [5.0.0]." +
+            " It should be re-indexed in Elasticsearch 5.x before upgrading to " + Version.CURRENT.toString() + ".");
 
         IndexMetaData goodMeta = newIndexMeta("foo", Settings.builder()
             .put(IndexMetaData.SETTING_VERSION_UPGRADED, Version.V_5_0_0_beta1)
             .put(IndexMetaData.SETTING_VERSION_CREATED, Version.fromString("5.1.0"))
             .put(IndexMetaData.SETTING_VERSION_MINIMUM_COMPATIBLE,
                 Version.CURRENT.luceneVersion.toString()).build());
-        service.upgradeIndexMetaData(goodMeta);
+        service.upgradeIndexMetaData(goodMeta, Version.V_5_0_0.minimumIndexCompatibilityVersion());
     }
 
     public static IndexMetaData newIndexMeta(String name, Settings indexSettings) {

core/src/test/java/org/elasticsearch/cluster/node/DiscoveryNodesTests.java

@@ -22,6 +22,7 @@ package org.elasticsearch.cluster.node;
 import com.carrotsearch.randomizedtesting.generators.RandomPicks;
 import org.elasticsearch.Version;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.VersionUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -250,4 +251,22 @@ public class DiscoveryNodesTests extends ESTestCase {
 
         abstract Set<String> matchingNodeIds(DiscoveryNodes nodes);
     }
+
+    public void testMaxMinNodeVersion() {
+        DiscoveryNodes.Builder discoBuilder = DiscoveryNodes.builder();
+        discoBuilder.add(new DiscoveryNode("name_" + 1, "node_" + 1, buildNewFakeTransportAddress(), Collections.emptyMap(),
+            new HashSet<>(randomSubsetOf(Arrays.asList(DiscoveryNode.Role.values()))),
+            Version.fromString("5.1.0")));
+        discoBuilder.add(new DiscoveryNode("name_" + 2, "node_" + 2, buildNewFakeTransportAddress(), Collections.emptyMap(),
+            new HashSet<>(randomSubsetOf(Arrays.asList(DiscoveryNode.Role.values()))),
+            Version.fromString("6.3.0")));
+        discoBuilder.add(new DiscoveryNode("name_" + 3, "node_" + 3, buildNewFakeTransportAddress(), Collections.emptyMap(),
+            new HashSet<>(randomSubsetOf(Arrays.asList(DiscoveryNode.Role.values()))),
+            Version.fromString("1.1.0")));
+        discoBuilder.localNodeId("name_1");
+        discoBuilder.masterNodeId("name_2");
+        DiscoveryNodes build = discoBuilder.build();
+        assertEquals( Version.fromString("6.3.0"), build.getMaxNodeVersion());
+        assertEquals( Version.fromString("1.1.0"), build.getMinNodeVersion());
+    }
 }

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

@@ -20,13 +20,16 @@
 package org.elasticsearch.discovery.zen;
 
 import java.io.Closeable;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.EnumSet;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.stream.Collectors;
 
 import org.apache.lucene.util.IOUtils;
@@ -35,22 +38,40 @@ import org.elasticsearch.action.support.replication.ClusterStateCreationUtils;
 import org.elasticsearch.cluster.ClusterChangedEvent;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNode.Role;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.routing.IndexRoutingTable;
+import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
+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.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.ESTestCase;
+import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.test.transport.MockTransportService;
 import org.elasticsearch.threadpool.TestThreadPool;
 import org.elasticsearch.threadpool.ThreadPool;
+import org.elasticsearch.transport.TransportChannel;
+import org.elasticsearch.transport.TransportResponse;
+import org.elasticsearch.transport.TransportResponseOptions;
 import org.elasticsearch.transport.TransportService;
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.emptySet;
+import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_CREATION_DATE;
+import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_REPLICAS;
+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.discovery.zen.ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING;
 import static org.elasticsearch.discovery.zen.ZenDiscovery.shouldIgnoreOrRejectNewClusterState;
 import static org.elasticsearch.test.ClusterServiceUtils.createClusterService;
@@ -283,4 +304,82 @@ public class ZenDiscoveryUnitTests extends ESTestCase {
         });
         return discoveryNodes;
     }
+
+    public void testValidateOnUnsupportedIndexVersionCreated() throws Exception {
+        final int iters = randomIntBetween(3, 10);
+        for (int i = 0; i < iters; i++) {
+            ClusterState.Builder stateBuilder = ClusterState.builder(ClusterName.DEFAULT);
+            final DiscoveryNode otherNode = new DiscoveryNode("other_node", buildNewFakeTransportAddress(), emptyMap(),
+                EnumSet.allOf(DiscoveryNode.Role.class), Version.CURRENT);
+            MembershipAction.ValidateJoinRequestRequestHandler request = new MembershipAction.ValidateJoinRequestRequestHandler();
+            final boolean incompatible = randomBoolean();
+            IndexMetaData indexMetaData = IndexMetaData.builder("test").settings(Settings.builder()
+                .put(SETTING_VERSION_CREATED, incompatible ? VersionUtils.getPreviousVersion(Version.CURRENT.minimumIndexCompatibilityVersion())
+                    : VersionUtils.randomVersionBetween(random(), Version.CURRENT.minimumIndexCompatibilityVersion(), Version.CURRENT))
+                .put(SETTING_NUMBER_OF_SHARDS, 1).put(SETTING_NUMBER_OF_REPLICAS, 0)
+                .put(SETTING_CREATION_DATE, System.currentTimeMillis()))
+                .state(IndexMetaData.State.OPEN)
+                .build();
+            IndexRoutingTable.Builder indexRoutingTableBuilder = IndexRoutingTable.builder(indexMetaData.getIndex());
+            RoutingTable.Builder routing = new RoutingTable.Builder();
+            routing.addAsNew(indexMetaData);
+            final ShardId shardId = new ShardId("test", "_na_", 0);
+            IndexShardRoutingTable.Builder indexShardRoutingBuilder = new IndexShardRoutingTable.Builder(shardId);
+
+            final DiscoveryNode primaryNode = otherNode;
+            indexShardRoutingBuilder.addShard(TestShardRouting.newShardRouting("test", 0, primaryNode.getId(), null, true,
+                ShardRoutingState.INITIALIZING, new UnassignedInfo(UnassignedInfo.Reason.INDEX_REOPENED, "getting there")));
+            indexRoutingTableBuilder.addIndexShard(indexShardRoutingBuilder.build());
+            IndexRoutingTable indexRoutingTable = indexRoutingTableBuilder.build();
+            IndexMetaData updatedIndexMetaData = updateActiveAllocations(indexRoutingTable, indexMetaData);
+            stateBuilder.metaData(MetaData.builder().put(updatedIndexMetaData, false).generateClusterUuidIfNeeded())
+                .routingTable(RoutingTable.builder().add(indexRoutingTable).build());
+            if (incompatible) {
+                IllegalStateException ex = expectThrows(IllegalStateException.class, () ->
+                    request.messageReceived(new MembershipAction.ValidateJoinRequest(stateBuilder.build()), null));
+                assertEquals("index [test] version not supported: "
+                    + VersionUtils.getPreviousVersion(Version.CURRENT.minimumCompatibilityVersion())
+                    + " minimum compatible index version is: " + Version.CURRENT.minimumCompatibilityVersion(), ex.getMessage());
+            } else {
+                AtomicBoolean sendResponse = new AtomicBoolean(false);
+                request.messageReceived(new MembershipAction.ValidateJoinRequest(stateBuilder.build()), new TransportChannel() {
+                    @Override
+                    public String action() {
+                        return null;
+                    }
+
+                    @Override
+                    public String getProfileName() {
+                        return null;
+                    }
+
+                    @Override
+                    public long getRequestId() {
+                        return 0;
+                    }
+
+                    @Override
+                    public String getChannelType() {
+                        return null;
+                    }
+
+                    @Override
+                    public void sendResponse(TransportResponse response) throws IOException {
+                        sendResponse.set(true);
+                    }
+
+                    @Override
+                    public void sendResponse(TransportResponse response, TransportResponseOptions options) throws IOException {
+
+                    }
+
+                    @Override
+                    public void sendResponse(Exception exception) throws IOException {
+
+                    }
+                });
+                assertTrue(sendResponse.get());
+            }
+        }
+    }
 }

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

@@ -414,7 +414,7 @@ public class GatewayIndexStateIT extends ESIntegTestCase {
         IndexMetaData metaData = state.getMetaData().index("test");
         for (NodeEnvironment services : internalCluster().getInstances(NodeEnvironment.class)) {
             IndexMetaData brokenMeta = IndexMetaData.builder(metaData).settings(Settings.builder().put(metaData.getSettings())
-                .put(IndexMetaData.SETTING_VERSION_CREATED, Version.V_5_0_0_beta1.id)
+                .put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT.minimumIndexCompatibilityVersion().id)
                  // this is invalid but should be archived
                 .put("index.similarity.BM25.type", "classic")
                  // this one is not validated ahead of time and breaks allocation

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

@@ -396,7 +396,7 @@ public class GatewayMetaStateTests extends ESAllocationTestCase {
             this.upgrade = upgrade;
         }
         @Override
-        public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData) {
+        public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData, Version minimumIndexCompatibilityVersion) {
             return upgrade ? IndexMetaData.builder(indexMetaData).build() : indexMetaData;
         }
     }

core/src/test/java/org/elasticsearch/indices/cluster/ClusterStateChanges.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.indices.cluster;
 
 import org.elasticsearch.ExceptionsHelper;
+import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.admin.cluster.reroute.ClusterRerouteRequest;
 import org.elasticsearch.action.admin.cluster.reroute.TransportClusterRerouteAction;
@@ -158,7 +159,7 @@ public class ClusterStateChanges extends AbstractComponent {
         MetaDataIndexUpgradeService metaDataIndexUpgradeService = new MetaDataIndexUpgradeService(settings, null, null) {
             // metaData upgrader should do nothing
             @Override
-            public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData) {
+            public IndexMetaData upgradeIndexMetaData(IndexMetaData indexMetaData, Version minimumIndexCompatibilityVersion) {
                 return indexMetaData;
             }
         };

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

@@ -142,7 +142,7 @@ public abstract class ESBackcompatTestCase extends ESIntegTestCase {
         }
         CompatibilityVersion annotation = clazz.getAnnotation(CompatibilityVersion.class);
         if (annotation != null) {
-            return Version.smallest(Version.fromId(annotation.version()), compatibilityVersion(clazz.getSuperclass()));
+            return Version.min(Version.fromId(annotation.version()), compatibilityVersion(clazz.getSuperclass()));
         }
         return compatibilityVersion(clazz.getSuperclass());
     }