YARN-7010. Federation: routing REST invocations transparently to multiple RMs (part 2 - getApps). (Contributed by Giovanni Matteo Fumarola via curino)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/conf/YarnConfiguration.java

@@ -2753,6 +2753,15 @@ public class YarnConfiguration extends Configuration {
       "org.apache.hadoop.yarn.server.router.webapp."
           + "DefaultRequestInterceptorREST";
 
+  /**
+   * The interceptor class used in FederationInterceptorREST should return
+   * partial AppReports.
+   */
+  public static final String ROUTER_WEBAPP_PARTIAL_RESULTS_ENABLED =
+      ROUTER_WEBAPP_PREFIX + "partial-result.enabled";
+  public static final boolean DEFAULT_ROUTER_WEBAPP_PARTIAL_RESULTS_ENABLED =
+      false;
+
   ////////////////////////////////
   // Other Configs
   ////////////////////////////////

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/test/java/org/apache/hadoop/yarn/conf/TestYarnConfigurationFields.java

@@ -159,6 +159,8 @@ public class TestYarnConfigurationFields extends TestConfigurationFieldsBase {
 
     configurationPrefixToSkipCompare
         .add(YarnConfiguration.ROUTER_CLIENTRM_SUBMIT_RETRY);
+    configurationPrefixToSkipCompare
+        .add(YarnConfiguration.ROUTER_WEBAPP_PARTIAL_RESULTS_ENABLED);
 
     // Set by container-executor.cfg
     configurationPrefixToSkipCompare.add(YarnConfiguration.NM_USER_HOME_DIR);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-common/src/main/java/org/apache/hadoop/yarn/server/uam/UnmanagedApplicationManager.java

@@ -83,7 +83,7 @@ public class UnmanagedApplicationManager {
   private static final Logger LOG =
       LoggerFactory.getLogger(UnmanagedApplicationManager.class);
   private static final long AM_STATE_WAIT_TIMEOUT_MS = 10000;
-  private static final String APP_NAME = "UnmanagedAM";
+  public static final String APP_NAME = "UnmanagedAM";
   private static final String DEFAULT_QUEUE_CONFIG = "uam.default.queue.name";
 
   private BlockingQueue<AsyncAllocateRequestInfo> requestQueue;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/dao/AppInfo.java

@@ -49,6 +49,7 @@ import org.apache.hadoop.yarn.server.resourcemanager.webapp.DeSelectFields.DeSel
 import org.apache.hadoop.yarn.util.Times;
 import org.apache.hadoop.yarn.webapp.util.WebAppUtils;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Joiner;
 
 @XmlRootElement(name = "app")
@@ -71,9 +72,9 @@ public class AppInfo {
   // these are ok for any user to see
   protected String id;
   protected String user;
-  protected String name;
+  private String name;
   protected String queue;
-  protected YarnApplicationState state;
+  private YarnApplicationState state;
   protected FinalApplicationStatus finalStatus;
   protected float progress;
   protected String trackingUI;
@@ -91,21 +92,21 @@ public class AppInfo {
   protected String amContainerLogs;
   protected String amHostHttpAddress;
   private String amRPCAddress;
-  protected long allocatedMB;
-  protected long allocatedVCores;
-  protected long reservedMB;
-  protected long reservedVCores;
-  protected int runningContainers;
-  protected long memorySeconds;
-  protected long vcoreSeconds;
+  private long allocatedMB;
+  private long allocatedVCores;
+  private long reservedMB;
+  private long reservedVCores;
+  private int runningContainers;
+  private long memorySeconds;
+  private long vcoreSeconds;
   protected float queueUsagePercentage;
   protected float clusterUsagePercentage;
 
   // preemption info fields
-  protected long preemptedResourceMB;
-  protected long preemptedResourceVCores;
-  protected int numNonAMContainerPreempted;
-  protected int numAMContainerPreempted;
+  private long preemptedResourceMB;
+  private long preemptedResourceVCores;
+  private int numNonAMContainerPreempted;
+  private int numAMContainerPreempted;
   private long preemptedMemorySeconds;
   private long preemptedVcoreSeconds;
 
@@ -142,12 +143,11 @@ public class AppInfo {
           || YarnApplicationState.NEW_SAVING == this.state
           || YarnApplicationState.SUBMITTED == this.state
           || YarnApplicationState.ACCEPTED == this.state;
-      this.trackingUI = this.trackingUrlIsNotReady ? "UNASSIGNED" : (app
-          .getFinishTime() == 0 ? "ApplicationMaster" : "History");
+      this.trackingUI = this.trackingUrlIsNotReady ? "UNASSIGNED"
+          : (app.getFinishTime() == 0 ? "ApplicationMaster" : "History");
       if (!trackingUrlIsNotReady) {
         this.trackingUrl =
-            WebAppUtils.getURLWithScheme(schemePrefix,
-                trackingUrl);
+            WebAppUtils.getURLWithScheme(schemePrefix, trackingUrl);
         this.trackingUrlPretty = this.trackingUrl;
       } else {
         this.trackingUrlPretty = "UNASSIGNED";
@@ -162,15 +162,15 @@ public class AppInfo {
       this.priority = 0;
 
       if (app.getApplicationPriority() != null) {
-        this.priority = app.getApplicationPriority()
-            .getPriority();
+        this.priority = app.getApplicationPriority().getPriority();
       }
       this.progress = app.getProgress() * 100;
       this.diagnostics = app.getDiagnostics().toString();
       if (diagnostics == null || diagnostics.isEmpty()) {
         this.diagnostics = "";
       }
-      if (app.getApplicationTags() != null && !app.getApplicationTags().isEmpty()) {
+      if (app.getApplicationTags() != null
+          && !app.getApplicationTags().isEmpty()) {
         this.applicationTags = Joiner.on(',').join(app.getApplicationTags());
       }
       this.finalStatus = app.getFinalApplicationStatus();
@@ -178,8 +178,8 @@ public class AppInfo {
       if (hasAccess) {
         this.startedTime = app.getStartTime();
         this.finishedTime = app.getFinishTime();
-        this.elapsedTime = Times.elapsed(app.getStartTime(),
-            app.getFinishTime());
+        this.elapsedTime =
+            Times.elapsed(app.getStartTime(), app.getFinishTime());
         this.logAggregationStatus = app.getLogAggregationStatusForAppReport();
         RMAppAttempt attempt = app.getCurrentAppAttempt();
         if (attempt != null) {
@@ -194,8 +194,8 @@ public class AppInfo {
 
           this.amRPCAddress = getAmRPCAddressFromRMAppAttempt(attempt);
 
-          ApplicationResourceUsageReport resourceReport = attempt
-              .getApplicationResourceUsageReport();
+          ApplicationResourceUsageReport resourceReport =
+              attempt.getApplicationResourceUsageReport();
           if (resourceReport != null) {
             Resource usedResources = resourceReport.getUsedResources();
             Resource reservedResources = resourceReport.getReservedResources();
@@ -208,9 +208,10 @@ public class AppInfo {
             clusterUsagePercentage = resourceReport.getClusterUsagePercentage();
           }
 
-          /* When the deSelects parameter contains "resourceRequests",
-             it skips returning massive ResourceRequest objects and vice versa.
-             Default behavior is no skipping. (YARN-6280)
+          /*
+           * When the deSelects parameter contains "resourceRequests", it skips
+           * returning massive ResourceRequest objects and vice versa. Default
+           * behavior is no skipping. (YARN-6280)
            */
           if (!deSelects.contains(DeSelectType.RESOURCE_REQUESTS)) {
             List<ResourceRequest> resourceRequestsRaw = rm.getRMContext()
@@ -228,12 +229,9 @@ public class AppInfo {
 
       // copy preemption info fields
       RMAppMetrics appMetrics = app.getRMAppMetrics();
-      numAMContainerPreempted =
-          appMetrics.getNumAMContainersPreempted();
-      preemptedResourceMB =
-          appMetrics.getResourcePreempted().getMemorySize();
-      numNonAMContainerPreempted =
-          appMetrics.getNumNonAMContainersPreempted();
+      numAMContainerPreempted = appMetrics.getNumAMContainersPreempted();
+      preemptedResourceMB = appMetrics.getResourcePreempted().getMemorySize();
+      numNonAMContainerPreempted = appMetrics.getNumNonAMContainersPreempted();
       preemptedResourceVCores =
           appMetrics.getResourcePreempted().getVirtualCores();
       memorySeconds = appMetrics.getMemorySeconds();
@@ -242,8 +240,7 @@ public class AppInfo {
       preemptedVcoreSeconds = appMetrics.getPreemptedVcoreSeconds();
       ApplicationSubmissionContext appSubmissionContext =
           app.getApplicationSubmissionContext();
-      unmanagedApplication =
-          appSubmissionContext.getUnmanagedAM();
+      unmanagedApplication = appSubmissionContext.getUnmanagedAM();
       appNodeLabelExpression =
           app.getApplicationSubmissionContext().getNodeLabelExpression();
       amNodeLabelExpression = (unmanagedApplication) ? null
@@ -286,6 +283,7 @@ public class AppInfo {
           timeouts.add(timeout);
         }
       }
+
     }
   }
 
@@ -417,22 +415,6 @@ public class AppInfo {
     return this.reservedVCores;
   }
 
-  public long getPreemptedMB() {
-    return preemptedResourceMB;
-  }
-
-  public long getPreemptedVCores() {
-    return preemptedResourceVCores;
-  }
-
-  public int getNumNonAMContainersPreempted() {
-    return numNonAMContainerPreempted;
-  }
-  
-  public int getNumAMContainersPreempted() {
-    return numAMContainerPreempted;
-  }
- 
   public long getMemorySeconds() {
     return memorySeconds;
   }
@@ -448,10 +430,15 @@ public class AppInfo {
   public long getPreemptedVcoreSeconds() {
     return preemptedVcoreSeconds;
   }
+
   public List<ResourceRequestInfo> getResourceRequests() {
     return this.resourceRequests;
   }
 
+  public void setResourceRequests(List<ResourceRequestInfo> resourceRequests) {
+    this.resourceRequests = resourceRequests;
+  }
+
   public LogAggregationStatus getLogAggregationStatus() {
     return this.logAggregationStatus;
   }
@@ -475,4 +462,89 @@ public class AppInfo {
   public ResourcesInfo getResourceInfo() {
     return resourceInfo;
   }
+
+  public long getPreemptedResourceMB() {
+    return preemptedResourceMB;
+  }
+
+  public void setPreemptedResourceMB(long preemptedResourceMB) {
+    this.preemptedResourceMB = preemptedResourceMB;
+  }
+
+  public long getPreemptedResourceVCores() {
+    return preemptedResourceVCores;
+  }
+
+  public void setPreemptedResourceVCores(long preemptedResourceVCores) {
+    this.preemptedResourceVCores = preemptedResourceVCores;
+  }
+
+  public int getNumNonAMContainerPreempted() {
+    return numNonAMContainerPreempted;
+  }
+
+  public void setNumNonAMContainerPreempted(int numNonAMContainerPreempted) {
+    this.numNonAMContainerPreempted = numNonAMContainerPreempted;
+  }
+
+  public int getNumAMContainerPreempted() {
+    return numAMContainerPreempted;
+  }
+
+  public void setNumAMContainerPreempted(int numAMContainerPreempted) {
+    this.numAMContainerPreempted = numAMContainerPreempted;
+  }
+
+  public void setPreemptedMemorySeconds(long preemptedMemorySeconds) {
+    this.preemptedMemorySeconds = preemptedMemorySeconds;
+  }
+
+  public void setPreemptedVcoreSeconds(long preemptedVcoreSeconds) {
+    this.preemptedVcoreSeconds = preemptedVcoreSeconds;
+  }
+
+  public void setAllocatedMB(long allocatedMB) {
+    this.allocatedMB = allocatedMB;
+  }
+
+  public void setAllocatedVCores(long allocatedVCores) {
+    this.allocatedVCores = allocatedVCores;
+  }
+
+  public void setReservedMB(long reservedMB) {
+    this.reservedMB = reservedMB;
+  }
+
+  public void setReservedVCores(long reservedVCores) {
+    this.reservedVCores = reservedVCores;
+  }
+
+  public void setRunningContainers(int runningContainers) {
+    this.runningContainers = runningContainers;
+  }
+
+  public void setMemorySeconds(long memorySeconds) {
+    this.memorySeconds = memorySeconds;
+  }
+
+  public void setVcoreSeconds(long vcoreSeconds) {
+    this.vcoreSeconds = vcoreSeconds;
+  }
+
+  public void setAppId(String appId) {
+    this.id = appId;
+  }
+
+  @VisibleForTesting
+  public void setAMHostHttpAddress(String amHost) {
+    this.amHostHttpAddress = amHost;
+  }
+
+  public void setState(YarnApplicationState state) {
+    this.state = state;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/dao/AppsInfo.java

@@ -40,4 +40,8 @@ public class AppsInfo {
     return app;
   }
 
+  public void addAll(ArrayList<AppInfo> appsInfo) {
+    app.addAll(appsInfo);
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/RouterMetrics.java

@@ -49,6 +49,8 @@ public final class RouterMetrics {
   private MutableGaugeInt numAppsFailedKilled;
   @Metric("# of application reports failed to be retrieved")
   private MutableGaugeInt numAppsFailedRetrieved;
+  @Metric("# of multiple applications reports failed to be retrieved")
+  private MutableGaugeInt numMultipleAppsFailedRetrieved;
 
   // Aggregate metrics are shared, and don't have to be looked up per call
   @Metric("Total number of successful Submitted apps and latency(ms)")
@@ -59,6 +61,9 @@ public final class RouterMetrics {
   private MutableRate totalSucceededAppsCreated;
   @Metric("Total number of successful Retrieved app reports and latency(ms)")
   private MutableRate totalSucceededAppsRetrieved;
+  @Metric("Total number of successful Retrieved multiple apps reports and "
+      + "latency(ms)")
+  private MutableRate totalSucceededMultipleAppsRetrieved;
 
   /**
    * Provide quantile counters for all latencies.
@@ -67,6 +72,7 @@ public final class RouterMetrics {
   private MutableQuantiles getNewApplicationLatency;
   private MutableQuantiles killApplicationLatency;
   private MutableQuantiles getApplicationReportLatency;
+  private MutableQuantiles getApplicationsReportLatency;
 
   private static volatile RouterMetrics INSTANCE = null;
   private static MetricsRegistry registry;
@@ -83,6 +89,9 @@ public final class RouterMetrics {
     getApplicationReportLatency =
         registry.newQuantiles("getApplicationReportLatency",
             "latency of get application report", "ops", "latency", 10);
+    getApplicationsReportLatency =
+        registry.newQuantiles("getApplicationsReportLatency",
+            "latency of get applications report", "ops", "latency", 10);
   }
 
   public static RouterMetrics getMetrics() {
@@ -124,6 +133,11 @@ public final class RouterMetrics {
     return totalSucceededAppsRetrieved.lastStat().numSamples();
   }
 
+  @VisibleForTesting
+  public long getNumSucceededMultipleAppsRetrieved() {
+    return totalSucceededMultipleAppsRetrieved.lastStat().numSamples();
+  }
+
   @VisibleForTesting
   public double getLatencySucceededAppsCreated() {
     return totalSucceededAppsCreated.lastStat().mean();
@@ -144,6 +158,11 @@ public final class RouterMetrics {
     return totalSucceededAppsRetrieved.lastStat().mean();
   }
 
+  @VisibleForTesting
+  public double getLatencySucceededMultipleGetAppReport() {
+    return totalSucceededMultipleAppsRetrieved.lastStat().mean();
+  }
+
   @VisibleForTesting
   public int getAppsFailedCreated() {
     return numAppsFailedCreated.value();
@@ -164,6 +183,11 @@ public final class RouterMetrics {
     return numAppsFailedRetrieved.value();
   }
 
+  @VisibleForTesting
+  public int getMultipleAppsFailedRetrieved() {
+    return numMultipleAppsFailedRetrieved.value();
+  }
+
   public void succeededAppsCreated(long duration) {
     totalSucceededAppsCreated.add(duration);
     getNewApplicationLatency.add(duration);
@@ -184,6 +208,11 @@ public final class RouterMetrics {
     getApplicationReportLatency.add(duration);
   }
 
+  public void succeededMultipleAppsRetrieved(long duration) {
+    totalSucceededMultipleAppsRetrieved.add(duration);
+    getApplicationsReportLatency.add(duration);
+  }
+
   public void incrAppsFailedCreated() {
     numAppsFailedCreated.incr();
   }
@@ -200,4 +229,8 @@ public final class RouterMetrics {
     numAppsFailedRetrieved.incr();
   }
 
+  public void incrMultipleAppsFailedRetrieved() {
+    numMultipleAppsFailedRetrieved.incr();
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/webapp/FederationInterceptorREST.java

@@ -25,6 +25,11 @@ import java.util.List;
 import java.util.Map;
 import java.util.Random;
 import java.util.Set;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorCompletionService;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
 
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -102,9 +107,15 @@ public class FederationInterceptorREST extends AbstractRESTRequestInterceptor {
   private RouterPolicyFacade policyFacade;
   private RouterMetrics routerMetrics;
   private final Clock clock = new MonotonicClock();
+  private boolean returnPartialReport;
 
   private Map<SubClusterId, DefaultRequestInterceptorREST> interceptors;
 
+  /**
+   * Thread pool used for asynchronous operations.
+   */
+  private ExecutorService threadpool;
+
   @Override
   public void init(String user) {
     federationFacade = FederationStateStoreFacade.getInstance();
@@ -125,6 +136,11 @@ public class FederationInterceptorREST extends AbstractRESTRequestInterceptor {
 
     interceptors = new HashMap<SubClusterId, DefaultRequestInterceptorREST>();
     routerMetrics = RouterMetrics.getMetrics();
+    threadpool = Executors.newCachedThreadPool();
+
+    returnPartialReport =
+        conf.getBoolean(YarnConfiguration.ROUTER_WEBAPP_PARTIAL_RESULTS_ENABLED,
+            YarnConfiguration.DEFAULT_ROUTER_WEBAPP_PARTIAL_RESULTS_ENABLED);
   }
 
   private SubClusterId getRandomActiveSubCluster(
@@ -586,6 +602,99 @@ public class FederationInterceptorREST extends AbstractRESTRequestInterceptor {
     return response;
   }
 
+  /**
+   * The Yarn Router will forward the request to all the Yarn RMs in parallel,
+   * after that it will group all the ApplicationReports by the ApplicationId.
+   * <p>
+   * Possible failure:
+   * <p>
+   * Client: identical behavior as {@code RMWebServices}.
+   * <p>
+   * Router: the Client will timeout and resubmit the request.
+   * <p>
+   * ResourceManager: the Router calls each Yarn RM in parallel by using one
+   * thread for each Yarn RM. In case a Yarn RM fails, a single call will
+   * timeout. However the Router will merge the ApplicationReports it got, and
+   * provides a partial list to the client.
+   * <p>
+   * State Store: the Router will timeout and it will retry depending on the
+   * FederationFacade settings - if the failure happened before the select
+   * operation.
+   */
+  @Override
+  public AppsInfo getApps(HttpServletRequest hsr, String stateQuery,
+      Set<String> statesQuery, String finalStatusQuery, String userQuery,
+      String queueQuery, String count, String startedBegin, String startedEnd,
+      String finishBegin, String finishEnd, Set<String> applicationTypes,
+      Set<String> applicationTags, Set<String> unselectedFields) {
+    AppsInfo apps = new AppsInfo();
+    long startTime = clock.getTime();
+
+    Map<SubClusterId, SubClusterInfo> subClustersActive = null;
+    try {
+      subClustersActive = federationFacade.getSubClusters(true);
+    } catch (YarnException e) {
+      routerMetrics.incrMultipleAppsFailedRetrieved();
+      return null;
+    }
+
+    // Send the requests in parallel
+
+    ExecutorCompletionService<AppsInfo> compSvc =
+        new ExecutorCompletionService<AppsInfo>(this.threadpool);
+
+    for (final SubClusterInfo info : subClustersActive.values()) {
+      compSvc.submit(new Callable<AppsInfo>() {
+        @Override
+        public AppsInfo call() {
+          DefaultRequestInterceptorREST interceptor =
+              getOrCreateInterceptorForSubCluster(info.getSubClusterId(),
+                  info.getClientRMServiceAddress());
+          AppsInfo rmApps = interceptor.getApps(hsr, stateQuery, statesQuery,
+              finalStatusQuery, userQuery, queueQuery, count, startedBegin,
+              startedEnd, finishBegin, finishEnd, applicationTypes,
+              applicationTags, unselectedFields);
+
+          if (rmApps == null) {
+            routerMetrics.incrMultipleAppsFailedRetrieved();
+            LOG.error("Subcluster " + info.getSubClusterId()
+                + " failed to return appReport.");
+            return null;
+          }
+          return rmApps;
+        }
+      });
+    }
+
+    // Collect all the responses in parallel
+
+    for (int i = 0; i < subClustersActive.values().size(); i++) {
+      try {
+        Future<AppsInfo> future = compSvc.take();
+        AppsInfo appsResponse = future.get();
+
+        long stopTime = clock.getTime();
+        routerMetrics.succeededMultipleAppsRetrieved(stopTime - startTime);
+
+        if (appsResponse != null) {
+          apps.addAll(appsResponse.getApps());
+        }
+      } catch (Throwable e) {
+        routerMetrics.incrMultipleAppsFailedRetrieved();
+        LOG.warn("Failed to get application report ", e);
+      }
+    }
+
+    if (apps.getApps().isEmpty()) {
+      return null;
+    }
+
+    // Merge all the application reports got from all the available Yarn RMs
+
+    return RouterWebServiceUtil.mergeAppsInfo(apps.getApps(),
+        returnPartialReport);
+  }
+
   @Override
   public ClusterInfo get() {
     return getClusterInfo();
@@ -639,15 +748,6 @@ public class FederationInterceptorREST extends AbstractRESTRequestInterceptor {
     throw new NotImplementedException();
   }
 
-  @Override
-  public AppsInfo getApps(HttpServletRequest hsr, String stateQuery,
-      Set<String> statesQuery, String finalStatusQuery, String userQuery,
-      String queueQuery, String count, String startedBegin, String startedEnd,
-      String finishBegin, String finishEnd, Set<String> applicationTypes,
-      Set<String> applicationTags, Set<String> unselectedFields) {
-    throw new NotImplementedException();
-  }
-
   @Override
   public AppState getAppState(HttpServletRequest hsr, String appId)
       throws AuthorizationException {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/webapp/RouterWebServiceUtil.java

@@ -20,6 +20,8 @@ package org.apache.hadoop.yarn.server.router.webapp;
 
 import java.io.IOException;
 import java.security.PrivilegedExceptionAction;
+import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -33,7 +35,11 @@ import javax.ws.rs.core.Response.ResponseBuilder;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.yarn.api.records.YarnApplicationState;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.RMWebAppUtil;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppsInfo;
+import org.apache.hadoop.yarn.server.uam.UnmanagedApplicationManager;
 import org.apache.hadoop.yarn.webapp.BadRequestException;
 import org.apache.hadoop.yarn.webapp.ForbiddenException;
 import org.apache.hadoop.yarn.webapp.NotFoundException;
@@ -55,6 +61,8 @@ public final class RouterWebServiceUtil {
   private static final Log LOG =
       LogFactory.getLog(RouterWebServiceUtil.class.getName());
 
+  private final static String PARTIAL_REPORT = "Partial Report ";
+
   /** Disable constructor. */
   private RouterWebServiceUtil() {
   }
@@ -224,4 +232,103 @@ public final class RouterWebServiceUtil {
 
   }
 
+  /**
+   * Merges a list of AppInfo grouping by ApplicationId. Our current policy
+   * is to merge the application reports from the reacheable SubClusters.
+   * Via configuration parameter, we decide whether to return applications
+   * for which the primary AM is missing or to omit them.
+   *
+   * @param appsInfo a list of AppInfo to merge
+   * @param returnPartialResult if the merge AppsInfo should contain partial
+   *          result or not
+   * @return the merged AppsInfo
+   */
+  public static AppsInfo mergeAppsInfo(ArrayList<AppInfo> appsInfo,
+      boolean returnPartialResult) {
+    AppsInfo allApps = new AppsInfo();
+
+    Map<String, AppInfo> federationAM = new HashMap<String, AppInfo>();
+    Map<String, AppInfo> federationUAMSum = new HashMap<String, AppInfo>();
+    for (AppInfo a : appsInfo) {
+      // Check if this AppInfo is an AM
+      if (a.getAMHostHttpAddress() != null) {
+        // Insert in the list of AM
+        federationAM.put(a.getAppId(), a);
+        // Check if there are any UAM found before
+        if (federationUAMSum.containsKey(a.getAppId())) {
+          // Merge the current AM with the found UAM
+          mergeAMWithUAM(a, federationUAMSum.get(a.getAppId()));
+          // Remove the sum of the UAMs
+          federationUAMSum.remove(a.getAppId());
+        }
+        // This AppInfo is an UAM
+      } else {
+        if (federationAM.containsKey(a.getAppId())) {
+          // Merge the current UAM with its own AM
+          mergeAMWithUAM(federationAM.get(a.getAppId()), a);
+        } else if (federationUAMSum.containsKey(a.getAppId())) {
+          // Merge the current UAM with its own UAM and update the list of UAM
+          federationUAMSum.put(a.getAppId(),
+              mergeUAMWithUAM(federationUAMSum.get(a.getAppId()), a));
+        } else {
+          // Insert in the list of UAM
+          federationUAMSum.put(a.getAppId(), a);
+        }
+      }
+    }
+
+    // Check the remaining UAMs are depending or not from federation
+    for (AppInfo a : federationUAMSum.values()) {
+      if (returnPartialResult || (a.getName() != null
+          && !(a.getName().startsWith(UnmanagedApplicationManager.APP_NAME)
+              || a.getName().startsWith(PARTIAL_REPORT)))) {
+        federationAM.put(a.getAppId(), a);
+      }
+    }
+
+    allApps.addAll(new ArrayList<AppInfo>(federationAM.values()));
+    return allApps;
+  }
+
+  private static AppInfo mergeUAMWithUAM(AppInfo uam1, AppInfo uam2) {
+    AppInfo partialReport = new AppInfo();
+    partialReport.setAppId(uam1.getAppId());
+    partialReport.setName(PARTIAL_REPORT + uam1.getAppId());
+    // We pick the status of the first uam
+    partialReport.setState(uam1.getState());
+    // Merge the newly partial AM with UAM1 and then with UAM2
+    mergeAMWithUAM(partialReport, uam1);
+    mergeAMWithUAM(partialReport, uam2);
+    return partialReport;
+  }
+
+  private static void mergeAMWithUAM(AppInfo am, AppInfo uam) {
+    am.setPreemptedResourceMB(
+        am.getPreemptedResourceMB() + uam.getPreemptedResourceMB());
+    am.setPreemptedResourceVCores(
+        am.getPreemptedResourceVCores() + uam.getPreemptedResourceVCores());
+    am.setNumNonAMContainerPreempted(am.getNumNonAMContainerPreempted()
+        + uam.getNumNonAMContainerPreempted());
+    am.setNumAMContainerPreempted(
+        am.getNumAMContainerPreempted() + uam.getNumAMContainerPreempted());
+    am.setPreemptedMemorySeconds(
+        am.getPreemptedMemorySeconds() + uam.getPreemptedMemorySeconds());
+    am.setPreemptedVcoreSeconds(
+        am.getPreemptedVcoreSeconds() + uam.getPreemptedVcoreSeconds());
+
+    if (am.getState() == YarnApplicationState.RUNNING
+        && uam.getState() == am.getState()) {
+
+      am.getResourceRequests().addAll(uam.getResourceRequests());
+
+      am.setAllocatedMB(am.getAllocatedMB() + uam.getAllocatedMB());
+      am.setAllocatedVCores(am.getAllocatedVCores() + uam.getAllocatedVCores());
+      am.setReservedMB(am.getReservedMB() + uam.getReservedMB());
+      am.setReservedVCores(am.getReservedVCores() + uam.getReservedMB());
+      am.setRunningContainers(
+          am.getRunningContainers() + uam.getRunningContainers());
+      am.setMemorySeconds(am.getMemorySeconds() + uam.getMemorySeconds());
+      am.setVcoreSeconds(am.getVcoreSeconds() + uam.getVcoreSeconds());
+    }
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/TestRouterMetrics.java

@@ -196,6 +196,45 @@ public class TestRouterMetrics {
     Assert.assertEquals(totalBadbefore + 1, metrics.getAppsFailedRetrieved());
   }
 
+  /**
+   * This test validates the correctness of the metric: Retrieved Multiple Apps
+   * successfully.
+   */
+  @Test
+  public void testSucceededMultipleAppsReport() {
+
+    long totalGoodBefore = metrics.getNumSucceededMultipleAppsRetrieved();
+
+    goodSubCluster.getApplicationsReport(100);
+
+    Assert.assertEquals(totalGoodBefore + 1,
+        metrics.getNumSucceededMultipleAppsRetrieved());
+    Assert.assertEquals(100, metrics.getLatencySucceededMultipleGetAppReport(),
+        0);
+
+    goodSubCluster.getApplicationsReport(200);
+
+    Assert.assertEquals(totalGoodBefore + 2,
+        metrics.getNumSucceededMultipleAppsRetrieved());
+    Assert.assertEquals(150, metrics.getLatencySucceededMultipleGetAppReport(),
+        0);
+  }
+
+  /**
+   * This test validates the correctness of the metric: Failed to retrieve
+   * Multiple Apps.
+   */
+  @Test
+  public void testMulipleAppsReportFailed() {
+
+    long totalBadbefore = metrics.getMultipleAppsFailedRetrieved();
+
+    badSubCluster.getApplicationsReport();
+
+    Assert.assertEquals(totalBadbefore + 1,
+        metrics.getMultipleAppsFailedRetrieved());
+  }
+
   // Records failures for all calls
   private class MockBadSubCluster {
     public void getNewApplication() {
@@ -217,6 +256,11 @@ public class TestRouterMetrics {
       LOG.info("Mocked: failed getApplicationReport call");
       metrics.incrAppsFailedRetrieved();
     }
+
+    public void getApplicationsReport() {
+      LOG.info("Mocked: failed getApplicationsReport call");
+      metrics.incrMultipleAppsFailedRetrieved();
+    }
   }
 
   // Records successes for all calls
@@ -244,5 +288,11 @@ public class TestRouterMetrics {
           duration);
       metrics.succeededAppsRetrieved(duration);
     }
+
+    public void getApplicationsReport(long duration) {
+      LOG.info("Mocked: successful getApplicationsReport call with duration {}",
+          duration);
+      metrics.succeededMultipleAppsRetrieved(duration);
+    }
   }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/MockDefaultRequestInterceptorREST.java

@@ -18,26 +18,32 @@
 
 package org.apache.hadoop.yarn.server.router.webapp;
 
-import org.apache.hadoop.security.authorize.AuthorizationException;
-import org.apache.hadoop.yarn.api.records.ApplicationId;
-import org.apache.hadoop.yarn.exceptions.ApplicationNotFoundException;
-import org.apache.hadoop.yarn.exceptions.YarnException;
-import org.apache.hadoop.yarn.server.federation.store.records.SubClusterId;
-import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.*;
-import org.apache.hadoop.yarn.webapp.NotFoundException;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import javax.servlet.http.HttpServletRequest;
-import javax.ws.rs.core.HttpHeaders;
-import javax.ws.rs.core.Response;
-import javax.ws.rs.core.Response.Status;
 import java.io.IOException;
 import java.net.ConnectException;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import javax.servlet.http.HttpServletRequest;
+import javax.ws.rs.core.HttpHeaders;
+import javax.ws.rs.core.Response;
+import javax.ws.rs.core.Response.Status;
+
+import org.apache.hadoop.security.authorize.AuthorizationException;
+import org.apache.hadoop.yarn.api.records.ApplicationId;
+import org.apache.hadoop.yarn.exceptions.ApplicationNotFoundException;
+import org.apache.hadoop.yarn.exceptions.YarnException;
+import org.apache.hadoop.yarn.server.federation.store.records.SubClusterId;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppState;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ApplicationSubmissionContextInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppsInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.NewApplication;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ResourceInfo;
+import org.apache.hadoop.yarn.webapp.NotFoundException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * This class mocks the RESTRequestInterceptor.
  */
@@ -100,6 +106,27 @@ public class MockDefaultRequestInterceptorREST
     return new AppInfo();
   }
 
+  @Override
+  public AppsInfo getApps(HttpServletRequest hsr, String stateQuery,
+      Set<String> statesQuery, String finalStatusQuery, String userQuery,
+      String queueQuery, String count, String startedBegin, String startedEnd,
+      String finishBegin, String finishEnd, Set<String> applicationTypes,
+      Set<String> applicationTags, Set<String> unselectedFields) {
+    if (!isRunning) {
+      throw new RuntimeException("RM is stopped");
+    }
+    AppsInfo appsInfo = new AppsInfo();
+    AppInfo appInfo = new AppInfo();
+
+    appInfo.setAppId(
+        ApplicationId.newInstance(Integer.valueOf(getSubClusterId().getId()),
+            applicationCounter.incrementAndGet()).toString());
+    appInfo.setAMHostHttpAddress("http://i_am_the_AM:1234");
+
+    appsInfo.add(appInfo);
+    return appsInfo;
+  }
+
   @Override
   public Response updateAppState(AppState targetState, HttpServletRequest hsr,
       String appId) throws AuthorizationException, YarnException,

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/TestFederationInterceptorREST.java

@@ -35,6 +35,7 @@ import org.apache.hadoop.yarn.server.federation.utils.FederationStateStoreTestUt
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppState;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ApplicationSubmissionContextInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppsInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.NewApplication;
 import org.junit.Assert;
 import org.junit.Test;
@@ -374,4 +375,20 @@ public class TestFederationInterceptorREST extends BaseRouterWebServicesTest {
     Assert.assertNull(response);
   }
 
+  /**
+   * This test validates the correctness of GetApplicationsReport in case each
+   * subcluster provided one application.
+   */
+  @Test
+  public void testGetApplicationsReport()
+      throws YarnException, IOException, InterruptedException {
+
+    AppsInfo responseGet = interceptor.getApps(null, null, null, null, null,
+        null, null, null, null, null, null, null, null, null);
+
+    Assert.assertNotNull(responseGet);
+    Assert.assertEquals(NUM_SUBCLUSTER, responseGet.getApps().size());
+    // The merged operations will be tested in TestRouterWebServiceUtil
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/TestFederationInterceptorRESTRetry.java

@@ -36,6 +36,7 @@ import org.apache.hadoop.yarn.server.federation.store.records.SubClusterId;
 import org.apache.hadoop.yarn.server.federation.utils.FederationStateStoreFacade;
 import org.apache.hadoop.yarn.server.federation.utils.FederationStateStoreTestUtil;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ApplicationSubmissionContextInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppsInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.NewApplication;
 import org.apache.hadoop.yarn.server.router.clientrm.PassThroughClientRequestInterceptor;
 import org.apache.hadoop.yarn.server.router.clientrm.TestableFederationClientInterceptor;
@@ -271,4 +272,48 @@ public class TestFederationInterceptorRESTRetry
             .getApplicationHomeSubCluster().getHomeSubCluster());
   }
 
+  /**
+   * This test validates the correctness of GetApps in case the cluster is
+   * composed of only 1 bad SubCluster.
+   */
+  @Test
+  public void testGetAppsOneBadSC()
+      throws YarnException, IOException, InterruptedException {
+
+    setupCluster(Arrays.asList(bad2));
+
+    AppsInfo response = interceptor.getApps(null, null, null, null, null, null,
+        null, null, null, null, null, null, null, null);
+    Assert.assertNull(response);
+  }
+
+  /**
+   * This test validates the correctness of GetApps in case the cluster is
+   * composed of only 2 bad SubClusters.
+   */
+  @Test
+  public void testGetAppsTwoBadSCs()
+      throws YarnException, IOException, InterruptedException {
+    setupCluster(Arrays.asList(bad1, bad2));
+
+    AppsInfo response = interceptor.getApps(null, null, null, null, null, null,
+        null, null, null, null, null, null, null, null);
+    Assert.assertNull(response);
+  }
+
+  /**
+   * This test validates the correctness of GetApps in case the cluster is
+   * composed of only 1 bad SubCluster and a good one.
+   */
+  @Test
+  public void testGetAppsOneBadOneGood()
+      throws YarnException, IOException, InterruptedException {
+    setupCluster(Arrays.asList(good, bad2));
+
+    AppsInfo response = interceptor.getApps(null, null, null, null, null, null,
+        null, null, null, null, null, null, null, null);
+    Assert.assertNotNull(response);
+    Assert.assertEquals(1, response.getApps().size());
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/TestRouterWebServiceUtil.java

@@ -0,0 +1,311 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.yarn.server.router.webapp;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.hadoop.yarn.api.records.ApplicationId;
+import org.apache.hadoop.yarn.api.records.YarnApplicationState;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppsInfo;
+import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ResourceRequestInfo;
+import org.apache.hadoop.yarn.server.uam.UnmanagedApplicationManager;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Test class to validate RouterWebServiceUtil methods.
+ */
+public class TestRouterWebServiceUtil {
+
+  private static final ApplicationId APPID1 = ApplicationId.newInstance(1, 1);
+  private static final ApplicationId APPID2 = ApplicationId.newInstance(2, 1);
+  private static final ApplicationId APPID3 = ApplicationId.newInstance(3, 1);
+  private static final ApplicationId APPID4 = ApplicationId.newInstance(4, 1);
+
+  /**
+   * This test validates the correctness of RouterWebServiceUtil#mergeAppsInfo
+   * in case we want to merge 4 AMs. The expected result would be the same 4
+   * AMs.
+   */
+  @Test
+  public void testMerge4DifferentApps() {
+
+    AppsInfo apps = new AppsInfo();
+    int value = 1000;
+
+    AppInfo app1 = new AppInfo();
+    app1.setAppId(APPID1.toString());
+    app1.setAMHostHttpAddress("http://i_am_the_AM1:1234");
+    app1.setState(YarnApplicationState.FINISHED);
+    app1.setNumAMContainerPreempted(value);
+    apps.add(app1);
+
+    AppInfo app2 = new AppInfo();
+    app2.setAppId(APPID2.toString());
+    app2.setAMHostHttpAddress("http://i_am_the_AM2:1234");
+    app2.setState(YarnApplicationState.ACCEPTED);
+    app2.setAllocatedVCores(2 * value);
+
+    apps.add(app2);
+
+    AppInfo app3 = new AppInfo();
+    app3.setAppId(APPID3.toString());
+    app3.setAMHostHttpAddress("http://i_am_the_AM3:1234");
+    app3.setState(YarnApplicationState.RUNNING);
+    app3.setReservedMB(3 * value);
+    apps.add(app3);
+
+    AppInfo app4 = new AppInfo();
+    app4.setAppId(APPID4.toString());
+    app4.setAMHostHttpAddress("http://i_am_the_AM4:1234");
+    app4.setState(YarnApplicationState.NEW);
+    app4.setAllocatedMB(4 * value);
+    apps.add(app4);
+
+    AppsInfo result = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(4, result.getApps().size());
+
+    List<String> appIds = new ArrayList<String>();
+    AppInfo appInfo1 = null, appInfo2 = null, appInfo3 = null, appInfo4 = null;
+    for (AppInfo app : result.getApps()) {
+      appIds.add(app.getAppId());
+      if (app.getAppId().equals(APPID1.toString())) {
+        appInfo1 = app;
+      }
+      if (app.getAppId().equals(APPID2.toString())) {
+        appInfo2 = app;
+      }
+      if (app.getAppId().equals(APPID3.toString())) {
+        appInfo3 = app;
+      }
+      if (app.getAppId().equals(APPID4.toString())) {
+        appInfo4 = app;
+      }
+    }
+
+    Assert.assertTrue(appIds.contains(APPID1.toString()));
+    Assert.assertTrue(appIds.contains(APPID2.toString()));
+    Assert.assertTrue(appIds.contains(APPID3.toString()));
+    Assert.assertTrue(appIds.contains(APPID4.toString()));
+
+    // Check preservations APP1
+    Assert.assertEquals(app1.getState(), appInfo1.getState());
+    Assert.assertEquals(app1.getNumAMContainerPreempted(),
+        appInfo1.getNumAMContainerPreempted());
+
+    // Check preservations APP2
+    Assert.assertEquals(app2.getState(), appInfo2.getState());
+    Assert.assertEquals(app3.getAllocatedVCores(),
+        appInfo3.getAllocatedVCores());
+
+    // Check preservations APP3
+    Assert.assertEquals(app3.getState(), appInfo3.getState());
+    Assert.assertEquals(app3.getReservedMB(), appInfo3.getReservedMB());
+
+    // Check preservations APP3
+    Assert.assertEquals(app4.getState(), appInfo4.getState());
+    Assert.assertEquals(app3.getAllocatedMB(), appInfo3.getAllocatedMB());
+  }
+
+  /**
+   * This test validates the correctness of RouterWebServiceUtil#mergeAppsInfo
+   * in case we want to merge 2 UAMs and their own AM. The status of the AM is
+   * FINISHED, so we check the correctness of the merging of the historical
+   * values. The expected result would be 1 report with the merged information.
+   */
+  @Test
+  public void testMergeAppsFinished() {
+
+    AppsInfo apps = new AppsInfo();
+
+    String amHost = "http://i_am_the_AM1:1234";
+    AppInfo am = new AppInfo();
+    am.setAppId(APPID1.toString());
+    am.setAMHostHttpAddress(amHost);
+    am.setState(YarnApplicationState.FINISHED);
+
+    int value = 1000;
+    setAppInfoFinished(am, value);
+
+    apps.add(am);
+
+    AppInfo uam1 = new AppInfo();
+    uam1.setAppId(APPID1.toString());
+    apps.add(uam1);
+
+    setAppInfoFinished(uam1, value);
+
+    AppInfo uam2 = new AppInfo();
+    uam2.setAppId(APPID1.toString());
+    apps.add(uam2);
+
+    setAppInfoFinished(uam2, value);
+
+    // in this case the result does not change if we enable partial result
+    AppsInfo result = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(1, result.getApps().size());
+
+    AppInfo app = result.getApps().get(0);
+
+    Assert.assertEquals(APPID1.toString(), app.getAppId());
+    Assert.assertEquals(amHost, app.getAMHostHttpAddress());
+    Assert.assertEquals(value * 3, app.getPreemptedResourceMB());
+    Assert.assertEquals(value * 3, app.getPreemptedResourceVCores());
+    Assert.assertEquals(value * 3, app.getNumNonAMContainerPreempted());
+    Assert.assertEquals(value * 3, app.getNumAMContainerPreempted());
+    Assert.assertEquals(value * 3, app.getPreemptedMemorySeconds());
+    Assert.assertEquals(value * 3, app.getPreemptedVcoreSeconds());
+  }
+
+  private void setAppInfoFinished(AppInfo am, int value) {
+    am.setPreemptedResourceMB(value);
+    am.setPreemptedResourceVCores(value);
+    am.setNumNonAMContainerPreempted(value);
+    am.setNumAMContainerPreempted(value);
+    am.setPreemptedMemorySeconds(value);
+    am.setPreemptedVcoreSeconds(value);
+  }
+
+  /**
+   * This test validates the correctness of RouterWebServiceUtil#mergeAppsInfo
+   * in case we want to merge 2 UAMs and their own AM. The status of the AM is
+   * RUNNING, so we check the correctness of the merging of the runtime values.
+   * The expected result would be 1 report with the merged information.
+   */
+  @Test
+  public void testMergeAppsRunning() {
+
+    AppsInfo apps = new AppsInfo();
+
+    String amHost = "http://i_am_the_AM2:1234";
+    AppInfo am = new AppInfo();
+    am.setAppId(APPID2.toString());
+    am.setAMHostHttpAddress(amHost);
+    am.setState(YarnApplicationState.RUNNING);
+
+    int value = 1000;
+    setAppInfoRunning(am, value);
+
+    apps.add(am);
+
+    AppInfo uam1 = new AppInfo();
+    uam1.setAppId(APPID2.toString());
+    uam1.setState(YarnApplicationState.RUNNING);
+    apps.add(uam1);
+
+    setAppInfoRunning(uam1, value);
+
+    AppInfo uam2 = new AppInfo();
+    uam2.setAppId(APPID2.toString());
+    uam2.setState(YarnApplicationState.RUNNING);
+    apps.add(uam2);
+
+    setAppInfoRunning(uam2, value);
+
+    // in this case the result does not change if we enable partial result
+    AppsInfo result = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(1, result.getApps().size());
+
+    AppInfo app = result.getApps().get(0);
+
+    Assert.assertEquals(APPID2.toString(), app.getAppId());
+    Assert.assertEquals(amHost, app.getAMHostHttpAddress());
+    Assert.assertEquals(value * 3, app.getAllocatedMB());
+    Assert.assertEquals(value * 3, app.getAllocatedVCores());
+    Assert.assertEquals(value * 3, app.getReservedMB());
+    Assert.assertEquals(value * 3, app.getReservedVCores());
+    Assert.assertEquals(value * 3, app.getRunningContainers());
+    Assert.assertEquals(value * 3, app.getMemorySeconds());
+    Assert.assertEquals(value * 3, app.getVcoreSeconds());
+    Assert.assertEquals(3, app.getResourceRequests().size());
+  }
+
+  private void setAppInfoRunning(AppInfo am, int value) {
+    am.getResourceRequests().add(new ResourceRequestInfo());
+    am.setAllocatedMB(value);
+    am.setAllocatedVCores(value);
+    am.setReservedMB(value);
+    am.setReservedVCores(value);
+    am.setRunningContainers(value);
+    am.setMemorySeconds(value);
+    am.setVcoreSeconds(value);
+  }
+
+  /**
+   * This test validates the correctness of RouterWebServiceUtil#mergeAppsInfo
+   * in case we want to merge 2 UAMs without their own AM. The expected result
+   * would be an empty report or a partial report of the 2 UAMs depending on the
+   * selected policy.
+   */
+  @Test
+  public void testMerge2UAM() {
+
+    AppsInfo apps = new AppsInfo();
+
+    AppInfo app1 = new AppInfo();
+    app1.setAppId(APPID1.toString());
+    app1.setName(UnmanagedApplicationManager.APP_NAME);
+    app1.setState(YarnApplicationState.RUNNING);
+    apps.add(app1);
+
+    AppInfo app2 = new AppInfo();
+    app2.setAppId(APPID1.toString());
+    app2.setName(UnmanagedApplicationManager.APP_NAME);
+    app2.setState(YarnApplicationState.RUNNING);
+    apps.add(app2);
+
+    AppsInfo result = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(0, result.getApps().size());
+
+    // By enabling partial result, the expected result would be a partial report
+    // of the 2 UAMs
+    AppsInfo result2 = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), true);
+    Assert.assertNotNull(result2);
+    Assert.assertEquals(1, result2.getApps().size());
+    Assert.assertEquals(YarnApplicationState.RUNNING,
+        result2.getApps().get(0).getState());
+  }
+
+  /**
+   * This test validates the correctness of RouterWebServiceUtil#mergeAppsInfo
+   * in case we want to merge 1 UAM that does not depend on Federation. The
+   * excepted result would be the same app report.
+   */
+  @Test
+  public void testMergeUAM() {
+
+    AppsInfo apps = new AppsInfo();
+
+    AppInfo app1 = new AppInfo();
+    app1.setAppId(APPID1.toString());
+    app1.setName("Test");
+    apps.add(app1);
+
+    // in this case the result does not change if we enable partial result
+    AppsInfo result = RouterWebServiceUtil.mergeAppsInfo(apps.getApps(), false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(1, result.getApps().size());
+  }
+}