Add a metric for the Akka cluster members count and is_leader.

Author: Matthew Hayter

src/main/java/com/arpnetworking/clusteraggregator/ClusterStatusCache.java

@@ -24,6 +24,8 @@
 import akka.cluster.Cluster;
 import akka.cluster.ClusterEvent;
 import com.arpnetworking.clusteraggregator.models.ShardAllocation;
+import com.arpnetworking.metrics.Metrics;
+import com.arpnetworking.metrics.MetricsFactory;
 import com.arpnetworking.utility.ParallelLeastShardAllocationStrategy;
 import com.google.common.base.Optional;
 import com.google.common.collect.ArrayListMultimap;
@@ -48,23 +50,27 @@
  * @author Brandon Arp (barp at groupon dot com)
  */
 public class ClusterStatusCache extends UntypedActor {
+
     /**
      * Creates a {@link akka.actor.Props} for use in Akka.
      *
      * @param cluster The cluster to reference.
+     * @param metricsFactory A <code>MetricsFactory</code> to use for metrics creation.
      * @return A new {@link akka.actor.Props}
      */
-    public static Props props(final Cluster cluster) {
-        return Props.create(ClusterStatusCache.class, cluster);
+    public static Props props(final Cluster cluster, final MetricsFactory metricsFactory) {
+        return Props.create(ClusterStatusCache.class, cluster, metricsFactory);
     }
 
     /**
      * Public constructor.
      *
      * @param cluster {@link akka.cluster.Cluster} whose state is cached
+     * @param metricsFactory A <code>MetricsFactory</code> to use for metrics creation.
      */
-    public ClusterStatusCache(final Cluster cluster) {
+    public ClusterStatusCache(final Cluster cluster, final MetricsFactory metricsFactory) {
         _cluster = cluster;
+        _metricsFactory = metricsFactory;
     }
 
     /**
@@ -102,7 +108,16 @@ public void onReceive(final Object message) throws Exception {
         if (!getSender().equals(getSelf())) {
             // Public messages
             if (message instanceof ClusterEvent.CurrentClusterState) {
-                _clusterState = Optional.of((ClusterEvent.CurrentClusterState) message);
+                final ClusterEvent.CurrentClusterState clusterState = (ClusterEvent.CurrentClusterState) message;
+                _clusterState = Optional.of(clusterState);
+
+                final Metrics metrics = _metricsFactory.create();
+                metrics.setGauge("akka/members_count", clusterState.members().size());
+                if (_cluster.selfAddress().equals(clusterState.getLeader())) {
+                    metrics.setGauge("akka/is_leader", 1);
+                } else {
+                    metrics.setGauge("akka/is_leader", 0);
+                }
             } else if (message instanceof GetRequest) {
                 sendResponse(getSender());
             } else if (message instanceof ParallelLeastShardAllocationStrategy.RebalanceNotification) {
@@ -137,6 +152,7 @@ private static String hostFromActorRef(final ActorRef shardRegion) {
     }
 
     private final Cluster _cluster;
+    private final MetricsFactory _metricsFactory;
     private Optional<ClusterEvent.CurrentClusterState> _clusterState = Optional.absent();
     @Nullable
     private Cancellable _pollTimer;

src/main/java/com/arpnetworking/clusteraggregator/GuiceModule.java

@@ -211,9 +211,10 @@ private ActorRef provideBookkeeperProxy(final ActorSystem system) {
     private ActorRef provideStatusCache(
             final ActorSystem system,
             @Named("bookkeeper-proxy") final ActorRef bookkeeperProxy,
-            @Named("periodic-statistics") final ActorRef periodicStats) {
+            @Named("periodic-statistics") final ActorRef periodicStats,
+            final MetricsFactory metricsFactory) {
         final Cluster cluster = Cluster.get(system);
-        final ActorRef clusterStatusCache = system.actorOf(ClusterStatusCache.props(cluster), "cluster-status");
+        final ActorRef clusterStatusCache = system.actorOf(ClusterStatusCache.props(cluster, metricsFactory), "cluster-status");
         return system.actorOf(Status.props(bookkeeperProxy, cluster, clusterStatusCache, periodicStats), "status");
     }