Integrate LeaderChecker with Coordinator

server/src/main/java/org/elasticsearch/cluster/coordination/Coordinator.java

@@ -78,10 +78,13 @@ public class Coordinator extends AbstractLifecycleComponent implements Discovery
     private final UnicastConfiguredHostsResolver configuredHostsResolver;
     private final TimeValue publishTimeout;
     private final PublicationTransportHandler publicationHandler;
+    private final LeaderChecker leaderChecker;
     @Nullable
     private Releasable electionScheduler;
     @Nullable
     private Releasable prevotingRound;
+    @Nullable
+    private Releasable leaderCheckScheduler;
     private AtomicLong maxTermSeen = new AtomicLong();
 
     private Mode mode;
@@ -108,10 +111,27 @@ public Coordinator(Settings settings, TransportService transportService, Allocat
         this.peerFinder = new CoordinatorPeerFinder(settings, transportService,
             new HandshakingTransportAddressConnector(settings, transportService), configuredHostsResolver);
         this.publicationHandler = new PublicationTransportHandler(transportService, this::handlePublishRequest, this::handleApplyCommit);
+        this.leaderChecker = new LeaderChecker(settings, transportService, getOnLeaderFailure());
 
         masterService.setClusterStateSupplier(this::getStateForMasterService);
     }
 
+    private Runnable getOnLeaderFailure() {
+        return new Runnable() {
+            @Override
+            public void run() {
+                synchronized (mutex) {
+                    becomeCandidate("onLeaderFailure");
+                }
+            }
+
+            @Override
+            public String toString() {
+                return "notification of leader failure";
+            }
+        };
+    }
+
     private void handleApplyCommit(ApplyCommitRequest applyCommitRequest) {
         synchronized (mutex) {
             logger.trace("handleApplyCommit: applying commit {}", applyCommitRequest);
@@ -233,6 +253,12 @@ void becomeCandidate(String method) {
             joinAccumulator = joinHelper.new CandidateJoinAccumulator();
 
             peerFinder.activate(coordinationState.get().getLastAcceptedState().nodes());
+            leaderChecker.setCurrentNodes(DiscoveryNodes.EMPTY_NODES);
+
+            if (leaderCheckScheduler != null) {
+                leaderCheckScheduler.close();
+                leaderCheckScheduler = null;
+            }
         }
 
         preVoteCollector.update(getPreVoteResponse(), null);
@@ -251,23 +277,35 @@ void becomeLeader(String method) {
         peerFinder.deactivate(getLocalNode());
         closePrevotingAndElectionScheduler();
         preVoteCollector.update(getPreVoteResponse(), getLocalNode());
+
+        assert leaderCheckScheduler == null : leaderCheckScheduler;
     }
 
     void becomeFollower(String method, DiscoveryNode leaderNode) {
         assert Thread.holdsLock(mutex) : "Coordinator mutex not held";
         logger.debug("{}: becoming FOLLOWER of [{}] (was {}, lastKnownLeader was [{}])", method, leaderNode, mode, lastKnownLeader);
 
+        final boolean restartLeaderChecker = (mode == Mode.FOLLOWER && Optional.of(leaderNode).equals(lastKnownLeader)) == false;
+
         if (mode != Mode.FOLLOWER) {
             mode = Mode.FOLLOWER;
             joinAccumulator.close(mode);
             joinAccumulator = new JoinHelper.FollowerJoinAccumulator();
+            leaderChecker.setCurrentNodes(DiscoveryNodes.EMPTY_NODES);
         }
 
         lastKnownLeader = Optional.of(leaderNode);
         peerFinder.deactivate(leaderNode);
         closePrevotingAndElectionScheduler();
         cancelActivePublication();
         preVoteCollector.update(getPreVoteResponse(), leaderNode);
+
+        if (restartLeaderChecker) {
+            if (leaderCheckScheduler != null) {
+                leaderCheckScheduler.close();
+            }
+            leaderCheckScheduler = leaderChecker.startLeaderChecker(leaderNode);
+        }
     }
 
     private PreVoteResponse getPreVoteResponse() {
@@ -339,6 +377,7 @@ public void invariant() {
                 assert getStateForMasterService().nodes().getMasterNodeId() != null
                     || getStateForMasterService().term() != getCurrentTerm() :
                     getStateForMasterService();
+                assert leaderCheckScheduler == null : leaderCheckScheduler;
             } else if (mode == Mode.FOLLOWER) {
                 assert coordinationState.get().electionWon() == false : getLocalNode() + " is FOLLOWER so electionWon() should be false";
                 assert lastKnownLeader.isPresent() && (lastKnownLeader.get().equals(getLocalNode()) == false);
@@ -347,12 +386,16 @@ assert getStateForMasterService().nodes().getMasterNodeId() != null
                 assert electionScheduler == null : electionScheduler;
                 assert prevotingRound == null : prevotingRound;
                 assert getStateForMasterService().nodes().getMasterNodeId() == null : getStateForMasterService();
+                assert leaderChecker.currentNodeIsMaster() == false;
+                assert leaderCheckScheduler != null;
             } else {
                 assert mode == Mode.CANDIDATE;
                 assert joinAccumulator instanceof JoinHelper.CandidateJoinAccumulator;
                 assert peerFinderLeader.isPresent() == false : peerFinderLeader;
                 assert prevotingRound == null || electionScheduler != null;
                 assert getStateForMasterService().nodes().getMasterNodeId() == null : getStateForMasterService();
+                assert leaderChecker.currentNodeIsMaster() == false;
+                assert leaderCheckScheduler == null : leaderCheckScheduler;
             }
         }
     }
@@ -577,6 +620,8 @@ public String toString() {
                         return "scheduled timeout for " + publication;
                     }
                 });
+
+                leaderChecker.setCurrentNodes(publishRequest.getAcceptedState().nodes());
                 publication.start(Collections.emptySet()); // TODO start failure detector and put faultyNodes here
             }
         } catch (Exception e) {

server/src/main/java/org/elasticsearch/cluster/coordination/LeaderChecker.java

@@ -77,7 +77,7 @@ public class LeaderChecker extends AbstractComponent {
     private final TransportService transportService;
     private final Runnable onLeaderFailure;
 
-    private volatile DiscoveryNodes lastPublishedDiscoveryNodes;
+    private volatile DiscoveryNodes discoveryNodes;
 
     public LeaderChecker(final Settings settings, final TransportService transportService, final Runnable onLeaderFailure) {
         super(settings);
@@ -111,19 +111,24 @@ public Releasable startLeaderChecker(final DiscoveryNode leader) {
      * isLocalNodeElectedMaster() should reflect whether this node is a leader, and nodeExists()
      * should indicate whether nodes are known publication targets or not.
      */
-    public void setLastPublishedDiscoveryNodes(DiscoveryNodes discoveryNodes) {
-        logger.trace("updating last-published nodes: {}", discoveryNodes);
-        lastPublishedDiscoveryNodes = discoveryNodes;
+    public void setCurrentNodes(DiscoveryNodes discoveryNodes) {
+        logger.trace("setCurrentNodes: {}", discoveryNodes);
+        this.discoveryNodes = discoveryNodes;
+    }
+
+    // For assertions
+    boolean currentNodeIsMaster() {
+        return discoveryNodes.isLocalNodeElectedMaster();
     }
 
     private void handleLeaderCheck(LeaderCheckRequest request, TransportChannel transportChannel, Task task) throws IOException {
-        final DiscoveryNodes lastPublishedDiscoveryNodes = this.lastPublishedDiscoveryNodes;
-        assert lastPublishedDiscoveryNodes != null;
+        final DiscoveryNodes discoveryNodes = this.discoveryNodes;
+        assert discoveryNodes != null;
 
-        if (lastPublishedDiscoveryNodes.isLocalNodeElectedMaster() == false) {
+        if (discoveryNodes.isLocalNodeElectedMaster() == false) {
             logger.debug("non-master handling {}", request);
             transportChannel.sendResponse(new CoordinationStateRejectedException("non-leader rejecting leader check"));
-        } else if (lastPublishedDiscoveryNodes.nodeExists(request.getSender()) == false) {
+        } else if (discoveryNodes.nodeExists(request.getSender()) == false) {
             logger.debug("leader check from unknown node: {}", request);
             transportChannel.sendResponse(new CoordinationStateRejectedException("leader check from unknown node"));
         } else {

server/src/test/java/org/elasticsearch/action/support/replication/TransportReplicationActionTests.java

@@ -1105,6 +1105,9 @@ public String toString() {
     }
 
     static class TestResponse extends ReplicationResponse {
+        TestResponse() {
+            setShardInfo(new ShardInfo());
+        }
     }
 
     private class TestAction extends TransportReplicationAction<Request, Request, TestResponse> {

server/src/test/java/org/elasticsearch/cluster/coordination/CoordinatorTests.java

@@ -41,6 +41,7 @@
 import org.elasticsearch.indices.cluster.FakeThreadPoolMasterService;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.disruption.DisruptableMockTransport;
+import org.elasticsearch.test.disruption.DisruptableMockTransport.ConnectionStatus;
 import org.elasticsearch.test.junit.annotations.TestLogging;
 import org.elasticsearch.transport.TransportService;
 import org.hamcrest.Matcher;
@@ -59,7 +60,11 @@
 import static org.elasticsearch.cluster.coordination.CoordinationStateTests.clusterState;
 import static org.elasticsearch.cluster.coordination.CoordinationStateTests.setValue;
 import static org.elasticsearch.cluster.coordination.CoordinationStateTests.value;
+import static org.elasticsearch.cluster.coordination.Coordinator.Mode.CANDIDATE;
 import static org.elasticsearch.cluster.coordination.Coordinator.Mode.FOLLOWER;
+import static org.elasticsearch.cluster.coordination.LeaderChecker.LEADER_CHECK_INTERVAL_SETTING;
+import static org.elasticsearch.cluster.coordination.LeaderChecker.LEADER_CHECK_RETRY_COUNT_SETTING;
+import static org.elasticsearch.cluster.coordination.LeaderChecker.LEADER_CHECK_TIMEOUT_SETTING;
 import static org.elasticsearch.node.Node.NODE_NAME_SETTING;
 import static org.elasticsearch.transport.TransportService.HANDSHAKE_ACTION_NAME;
 import static org.elasticsearch.transport.TransportService.NOOP_TRANSPORT_INTERCEPTOR;
@@ -68,7 +73,7 @@
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 
-@TestLogging("org.elasticsearch.cluster.coordination:TRACE,org.elasticsearch.cluster.discovery:TRACE")
+@TestLogging("org.elasticsearch.cluster.coordination:TRACE,org.elasticsearch.discovery:TRACE")
 public class CoordinatorTests extends ESTestCase {
 
     public void testCanUpdateClusterStateAfterStabilisation() {
@@ -101,6 +106,40 @@ public void testNodesJoinAfterStableCluster() {
         assertEquals(currentTerm, newTerm);
     }
 
+    public void testLeaderDisconnectionDetectedQuickly() {
+        final Cluster cluster = new Cluster(randomIntBetween(3, 5));
+        cluster.stabilise();
+
+        final ClusterNode originalLeader = cluster.getAnyLeader();
+        logger.info("--> disconnecting leader {}", originalLeader);
+        originalLeader.disconnect();
+
+        synchronized (originalLeader.coordinator.mutex) {
+            originalLeader.coordinator.becomeCandidate("simulated failure detection"); // TODO remove once follower checker is integrated
+        }
+
+        cluster.stabilise();
+        assertThat(cluster.getAnyLeader().getId(), not(equalTo(originalLeader.getId())));
+    }
+
+    public void testUnresponsiveLeaderDetectedEventually() {
+        final Cluster cluster = new Cluster(randomIntBetween(3, 5));
+        cluster.stabilise();
+
+        final ClusterNode originalLeader = cluster.getAnyLeader();
+        logger.info("--> partitioning leader {}", originalLeader);
+        originalLeader.partition();
+
+        synchronized (originalLeader.coordinator.mutex) {
+            originalLeader.coordinator.becomeCandidate("simulated failure detection"); // TODO remove once follower checker is integrated
+        }
+
+        cluster.stabilise(Cluster.DEFAULT_STABILISATION_TIME
+            + (LEADER_CHECK_INTERVAL_SETTING.get(Settings.EMPTY).millis() + LEADER_CHECK_TIMEOUT_SETTING.get(Settings.EMPTY).millis())
+            * LEADER_CHECK_RETRY_COUNT_SETTING.get(Settings.EMPTY));
+        assertThat(cluster.getAnyLeader().getId(), not(equalTo(originalLeader.getId())));
+    }
+
     private static String nodeIdFromIndex(int nodeIndex) {
         return "node" + nodeIndex;
     }
@@ -115,6 +154,9 @@ class Cluster {
             Settings.builder().put(NODE_NAME_SETTING.getKey(), "deterministic-task-queue").build());
         private final VotingConfiguration initialConfiguration;
 
+        private final Set<String> disconnectedNodes = new HashSet<>();
+        private final Set<String> blackholedNodes = new HashSet<>();
+
         Cluster(int initialNodeCount) {
             logger.info("--> creating cluster of {} nodes", initialNodeCount);
 
@@ -142,8 +184,12 @@ void addNodes(int newNodesCount) {
         }
 
         void stabilise() {
+            stabilise(DEFAULT_STABILISATION_TIME);
+        }
+
+        void stabilise(long stabilisationTime) {
             final long stabilisationStartTime = deterministicTaskQueue.getCurrentTimeMillis();
-            while (deterministicTaskQueue.getCurrentTimeMillis() < stabilisationStartTime + DEFAULT_STABILISATION_TIME) {
+            while (deterministicTaskQueue.getCurrentTimeMillis() < stabilisationStartTime + stabilisationTime) {
 
                 while (deterministicTaskQueue.hasRunnableTasks()) {
                     try {
@@ -182,16 +228,21 @@ private void assertUniqueLeaderAndExpectedModes() {
                 }
 
                 final String nodeId = clusterNode.getId();
-                assertThat(nodeId + " has the same term as the leader", clusterNode.coordinator.getCurrentTerm(), is(leaderTerm));
-                // TODO assert that all nodes have actually voted for the leader in this term
-
-                assertThat(nodeId + " is a follower", clusterNode.coordinator.getMode(), is(FOLLOWER));
-                assertThat(nodeId + " is at the same accepted version as the leader",
-                    Optional.of(clusterNode.coordinator.getLastAcceptedState().getVersion()), isPresentAndEqualToLeaderVersion);
-                assertThat(nodeId + " is at the same committed version as the leader",
-                    clusterNode.coordinator.getLastCommittedState().map(ClusterState::getVersion), isPresentAndEqualToLeaderVersion);
-                assertThat(clusterNode.coordinator.getLastCommittedState().map(ClusterState::getNodes).map(dn -> dn.nodeExists(nodeId)),
-                    equalTo(Optional.of(true)));
+
+                if (disconnectedNodes.contains(nodeId) || blackholedNodes.contains(nodeId)) {
+                    assertThat(nodeId + " is a candidate", clusterNode.coordinator.getMode(), is(CANDIDATE));
+                } else {
+                    assertThat(nodeId + " has the same term as the leader", clusterNode.coordinator.getCurrentTerm(), is(leaderTerm));
+                    // TODO assert that all nodes have actually voted for the leader in this term
+
+                    assertThat(nodeId + " is a follower", clusterNode.coordinator.getMode(), is(FOLLOWER));
+                    assertThat(nodeId + " is at the same accepted version as the leader",
+                        Optional.of(clusterNode.coordinator.getLastAcceptedState().getVersion()), isPresentAndEqualToLeaderVersion);
+                    assertThat(nodeId + " is at the same committed version as the leader",
+                        clusterNode.coordinator.getLastCommittedState().map(ClusterState::getVersion), isPresentAndEqualToLeaderVersion);
+                    assertThat(clusterNode.coordinator.getLastCommittedState().map(ClusterState::getNodes).map(dn -> dn.nodeExists(nodeId)),
+                        equalTo(Optional.of(true)));
+                }
             }
 
             assertThat(leader.coordinator.getLastCommittedState().map(ClusterState::getNodes).map(DiscoveryNodes::getSize),
@@ -204,6 +255,18 @@ ClusterNode getAnyLeader() {
             return randomFrom(allLeaders);
         }
 
+        private ConnectionStatus getConnectionStatus(DiscoveryNode sender, DiscoveryNode destination) {
+            ConnectionStatus connectionStatus;
+            if (blackholedNodes.contains(sender.getId()) || blackholedNodes.contains(destination.getId())) {
+                connectionStatus = ConnectionStatus.BLACK_HOLE;
+            } else if (disconnectedNodes.contains(sender.getId()) || disconnectedNodes.contains(destination.getId())) {
+                connectionStatus = ConnectionStatus.DISCONNECTED;
+            } else {
+                connectionStatus = ConnectionStatus.CONNECTED;
+            }
+            return connectionStatus;
+        }
+
         class ClusterNode extends AbstractComponent {
             private final int nodeIndex;
             private Coordinator coordinator;
@@ -241,7 +304,7 @@ protected DiscoveryNode getLocalNode() {
 
                     @Override
                     protected ConnectionStatus getConnectionStatus(DiscoveryNode sender, DiscoveryNode destination) {
-                        return ConnectionStatus.CONNECTED;
+                        return Cluster.this.getConnectionStatus(sender, destination);
                     }
 
                     @Override
@@ -264,6 +327,17 @@ protected void handle(DiscoveryNode sender, DiscoveryNode destination, String ac
                             deterministicTaskQueue.scheduleNow(onNode(destination, doDelivery));
                         }
                     }
+
+                    @Override
+                    protected void onBlackholedDuringSend(long requestId, String action, DiscoveryNode destination) {
+                        if (action.equals(HANDSHAKE_ACTION_NAME)) {
+                            logger.trace("ignoring blackhole and delivering {}", getRequestDescription(requestId, action, destination));
+                            // handshakes always have a timeout, and are sent in a blocking fashion, so we must respond with an exception.
+                            sendFromTo(destination, getLocalNode(), action, getDisconnectException(requestId, action, destination));
+                        } else {
+                            super.onBlackholedDuringSend(requestId, action, destination);
+                        }
+                    }
                 };
 
                 masterService = new FakeThreadPoolMasterService("test",
@@ -290,7 +364,7 @@ String getId() {
                 return localNode.getId();
             }
 
-            public DiscoveryNode getLocalNode() {
+            DiscoveryNode getLocalNode() {
                 return localNode;
             }
 
@@ -316,6 +390,14 @@ public void onFailure(String source, Exception e) {
             public String toString() {
                 return localNode.toString();
             }
+
+            void disconnect() {
+                disconnectedNodes.add(localNode.getId());
+            }
+
+            void partition() {
+                blackholedNodes.add(localNode.getId());
+            }
         }
 
         private List<TransportAddress> provideUnicastHosts(HostsResolver ignored) {