order

This paper mainly studies the leader elector of storm nimbus

Nimbus

org/apache/storm/daemon/nimbus/Nimbus.java

    public static void main(String[] args) throws Exception {
        Utils.setupDefaultUncaughtExceptionHandler();
        launch(new StandaloneINimbus());
    }

    public static Nimbus launch(INimbus inimbus) throws Exception {
        Map<String, Object> conf = Utils.merge(ConfigUtils.readStormConfig(),
                                               ConfigUtils.readYamlConfig("storm-cluster-auth.yaml", false));
        boolean fixupAcl = (boolean) conf.get(DaemonConfig.STORM_NIMBUS_ZOOKEEPER_ACLS_FIXUP);
        boolean checkAcl = fixupAcl || (boolean) conf.get(DaemonConfig.STORM_NIMBUS_ZOOKEEPER_ACLS_CHECK);
        if (checkAcl) {
            AclEnforcement.verifyAcls(conf, fixupAcl);
        }
        return launchServer(conf, inimbus);
    }

    private static Nimbus launchServer(Map<String, Object> conf, INimbus inimbus) throws Exception {
        StormCommon.validateDistributedMode(conf);
        validatePortAvailable(conf);
        StormMetricsRegistry metricsRegistry = new StormMetricsRegistry();
        final Nimbus nimbus = new Nimbus(conf, inimbus, metricsRegistry);
        nimbus.launchServer();
        final ThriftServer server = new ThriftServer(conf, new Processor<>(nimbus), ThriftConnectionType.NIMBUS);
        metricsRegistry.startMetricsReporters(conf);
        Utils.addShutdownHookWithDelayedForceKill(() -> {
            metricsRegistry.stopMetricsReporters();
            nimbus.shutdown();
            server.stop();
        }, 10);
        if (ClientAuthUtils.areWorkerTokensEnabledServer(server, conf)) {
            nimbus.initWorkerTokenManager();
        }
        LOG.info("Starting nimbus server for storm version '{}'", STORM_VERSION);
        server.serve();
        return nimbus;
    }

    public Nimbus(Map<String, Object> conf, INimbus inimbus, IStormClusterState stormClusterState, NimbusInfo hostPortInfo,
                  BlobStore blobStore, TopoCache topoCache, ILeaderElector leaderElector, IGroupMappingServiceProvider groupMapper,
                  StormMetricsRegistry metricsRegistry)
        throws Exception {
        //......

        if (blobStore == null) {
            blobStore = ServerUtils.getNimbusBlobStore(conf, this.nimbusHostPortInfo, null);
        }
        this.blobStore = blobStore;

        if (topoCache == null) {
            topoCache = new TopoCache(blobStore, conf);
        }
        if (leaderElector == null) {
            leaderElector = Zookeeper.zkLeaderElector(conf, zkClient, blobStore, topoCache, stormClusterState, getNimbusAcls(conf),
                metricsRegistry);
        }
        this.leaderElector = leaderElector;
        this.blobStore.setLeaderElector(this.leaderElector);

        //......
    }

    public void launchServer() throws Exception {
        try {
            BlobStore store = blobStore;
            IStormClusterState state = stormClusterState;
            NimbusInfo hpi = nimbusHostPortInfo;

            LOG.info("Starting Nimbus with conf {}", ConfigUtils.maskPasswords(conf));
            validator.prepare(conf);

            //add to nimbuses
            state.addNimbusHost(hpi.getHost(),
                                new NimbusSummary(hpi.getHost(), hpi.getPort(), Time.currentTimeSecs(), false, STORM_VERSION));
            leaderElector.addToLeaderLockQueue();
            this.blobStore.startSyncBlobs();
            
            for (ClusterMetricsConsumerExecutor exec: clusterConsumerExceutors) {
                exec.prepare();
            }

            if (isLeader()) {
                for (String topoId : state.activeStorms()) {
                    transition(topoId, TopologyActions.STARTUP, null);
                }
                clusterMetricSet.setActive(true);
            }

            //......
        } catch (Exception e) {
            if (Utils.exceptionCauseIsInstanceOf(InterruptedException.class, e)) {
                throw e;
            }

            if (Utils.exceptionCauseIsInstanceOf(InterruptedIOException.class, e)) {
                throw e;
            }
            LOG.error("Error on initialization of nimbus", e);
            Utils.exitProcess(13, "Error on initialization of nimbus");
        }
    }

• Nimbus calls Zookeeper.zkLeaderElector in the constructor to create a leaderElector
• launchServer method called leaderElector.addToLeaderLockQueue() to participate in leader election

Zookeeper.zkLeaderElector

storm-core-1.1.0-sources.jar!/org/apache/storm/zookeeper/Zookeeper.java

    public static ILeaderElector zkLeaderElector(Map conf, BlobStore blobStore) throws UnknownHostException {
        return _instance.zkLeaderElectorImpl(conf, blobStore);
    }

    protected ILeaderElector zkLeaderElectorImpl(Map conf, BlobStore blobStore) throws UnknownHostException {
        List<String> servers = (List<String>) conf.get(Config.STORM_ZOOKEEPER_SERVERS);
        Object port = conf.get(Config.STORM_ZOOKEEPER_PORT);
        CuratorFramework zk = mkClientImpl(conf, servers, port, "", conf);
        String leaderLockPath = conf.get(Config.STORM_ZOOKEEPER_ROOT) + "/leader-lock";
        String id = NimbusInfo.fromConf(conf).toHostPortString();
        AtomicReference<LeaderLatch> leaderLatchAtomicReference = new AtomicReference<>(new LeaderLatch(zk, leaderLockPath, id));
        AtomicReference<LeaderLatchListener> leaderLatchListenerAtomicReference =
                new AtomicReference<>(leaderLatchListenerImpl(conf, zk, blobStore, leaderLatchAtomicReference.get()));
        return new LeaderElectorImp(conf, servers, zk, leaderLockPath, id, leaderLatchAtomicReference,
            leaderLatchListenerAtomicReference, blobStore);
    }

• Here we create a LeaderLatch using the / leader lock path, and then a LeaderLatchListener using the leaderlatchlistenrimpl
• Finally, create ILeaderElector with leaderelectorimpip

leaderLatchListenerImpl

storm-core-1.1.0-sources.jar!/org/apache/storm/zookeeper/Zookeeper.java

    // Leader latch listener that will be invoked when we either gain or lose leadership
    public static LeaderLatchListener leaderLatchListenerImpl(final Map conf, final CuratorFramework zk, final BlobStore blobStore, final LeaderLatch leaderLatch) throws UnknownHostException {
        final String hostName = InetAddress.getLocalHost().getCanonicalHostName();
        return new LeaderLatchListener() {
            final String STORM_JAR_SUFFIX = "-stormjar.jar";
            final String STORM_CODE_SUFFIX = "-stormcode.ser";
            final String STORM_CONF_SUFFIX = "-stormconf.ser";

            @Override
            public void isLeader() {
                Set<String> activeTopologyIds = new TreeSet<>(Zookeeper.getChildren(zk, conf.get(Config.STORM_ZOOKEEPER_ROOT) + ClusterUtils.STORMS_SUBTREE, false));

                Set<String> activeTopologyBlobKeys = populateTopologyBlobKeys(activeTopologyIds);
                Set<String> activeTopologyCodeKeys = filterTopologyCodeKeys(activeTopologyBlobKeys);
                Set<String> allLocalBlobKeys = Sets.newHashSet(blobStore.listKeys());
                Set<String> allLocalTopologyBlobKeys = filterTopologyBlobKeys(allLocalBlobKeys);

                // this finds all active topologies blob keys from all local topology blob keys
                Sets.SetView<String> diffTopology = Sets.difference(activeTopologyBlobKeys, allLocalTopologyBlobKeys);
                LOG.info("active-topology-blobs [{}] local-topology-blobs [{}] diff-topology-blobs [{}]",
                        generateJoinedString(activeTopologyIds), generateJoinedString(allLocalTopologyBlobKeys),
                        generateJoinedString(diffTopology));

                if (diffTopology.isEmpty()) {
                    Set<String> activeTopologyDependencies = getTopologyDependencyKeys(activeTopologyCodeKeys);

                    // this finds all dependency blob keys from active topologies from all local blob keys
                    Sets.SetView<String> diffDependencies = Sets.difference(activeTopologyDependencies, allLocalBlobKeys);
                    LOG.info("active-topology-dependencies [{}] local-blobs [{}] diff-topology-dependencies [{}]",
                            generateJoinedString(activeTopologyDependencies), generateJoinedString(allLocalBlobKeys),
                            generateJoinedString(diffDependencies));

                    if (diffDependencies.isEmpty()) {
                        LOG.info("Accepting leadership, all active topologies and corresponding dependencies found locally.");
                    } else {
                        LOG.info("Code for all active topologies is available locally, but some dependencies are not found locally, giving up leadership.");
                        closeLatch();
                    }
                } else {
                    LOG.info("code for all active topologies not available locally, giving up leadership.");
                    closeLatch();
                }
            }

            @Override
            public void notLeader() {
                LOG.info("{} lost leadership.", hostName);
            }

            //......

            private void closeLatch() {
                try {
                    leaderLatch.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        };
    }

• leaderLatchListenerImpl returns an implementation class of the LeaderLatchListener interface
• Some checks have been made in the isLeader interface, that is, when the leader is selected by zookeeper, if there are no active topologies or dependencies in the local area, you need to call leaderLatch.close() to give up the leadership
• The notLeader interface mainly prints the log

LeaderElectorImp

org/apache/storm/zookeeper/LeaderElectorImp.java

public class LeaderElectorImp implements ILeaderElector {
    private static Logger LOG = LoggerFactory.getLogger(LeaderElectorImp.class);
    private final Map<String, Object> conf;
    private final List<String> servers;
    private final CuratorFramework zk;
    private final String leaderlockPath;
    private final String id;
    private final AtomicReference<LeaderLatch> leaderLatch;
    private final AtomicReference<LeaderLatchListener> leaderLatchListener;
    private final BlobStore blobStore;
    private final TopoCache tc;
    private final IStormClusterState clusterState;
    private final List<ACL> acls;
    private final StormMetricsRegistry metricsRegistry;

    public LeaderElectorImp(Map<String, Object> conf, List<String> servers, CuratorFramework zk, String leaderlockPath, String id,
                            AtomicReference<LeaderLatch> leaderLatch, AtomicReference<LeaderLatchListener> leaderLatchListener,
                            BlobStore blobStore, final TopoCache tc, IStormClusterState clusterState, List<ACL> acls,
                            StormMetricsRegistry metricsRegistry) {
        this.conf = conf;
        this.servers = servers;
        this.zk = zk;
        this.leaderlockPath = leaderlockPath;
        this.id = id;
        this.leaderLatch = leaderLatch;
        this.leaderLatchListener = leaderLatchListener;
        this.blobStore = blobStore;
        this.tc = tc;
        this.clusterState = clusterState;
        this.acls = acls;
        this.metricsRegistry = metricsRegistry;
    }

    @Override
    public void prepare(Map<String, Object> conf) {
        // no-op for zookeeper implementation
    }

    @Override
    public void addToLeaderLockQueue() throws Exception {
        // if this latch is already closed, we need to create new instance.
        if (LeaderLatch.State.CLOSED.equals(leaderLatch.get().getState())) {
            leaderLatch.set(new LeaderLatch(zk, leaderlockPath));
            LeaderListenerCallback callback = new LeaderListenerCallback(conf, zk, leaderLatch.get(), blobStore, tc, clusterState, acls,
                metricsRegistry);
            leaderLatchListener.set(Zookeeper.leaderLatchListenerImpl(callback));
            LOG.info("LeaderLatch was in closed state. Resetted the leaderLatch and listeners.");
        }
        // Only if the latch is not already started we invoke start
        if (LeaderLatch.State.LATENT.equals(leaderLatch.get().getState())) {
            leaderLatch.get().addListener(leaderLatchListener.get());
            leaderLatch.get().start();
            LOG.info("Queued up for leader lock.");
        } else {
            LOG.info("Node already in queue for leader lock.");
        }
    }

    @Override
    // Only started latches can be closed.
    public void removeFromLeaderLockQueue() throws Exception {
        if (LeaderLatch.State.STARTED.equals(leaderLatch.get().getState())) {
            leaderLatch.get().close();
            LOG.info("Removed from leader lock queue.");
        } else {
            LOG.info("leader latch is not started so no removeFromLeaderLockQueue needed.");
        }
    }

    @Override
    public boolean isLeader() throws Exception {
        return leaderLatch.get().hasLeadership();
    }

    @Override
    public NimbusInfo getLeader() {
        try {
            return Zookeeper.toNimbusInfo(leaderLatch.get().getLeader());
        } catch (Exception e) {
            throw Utils.wrapInRuntime(e);
        }
    }

    @Override
    public List<NimbusInfo> getAllNimbuses() throws Exception {
        List<NimbusInfo> nimbusInfos = new ArrayList<>();
        Collection<Participant> participants = leaderLatch.get().getParticipants();
        for (Participant participant : participants) {
            nimbusInfos.add(Zookeeper.toNimbusInfo(participant));
        }
        return nimbusInfos;
    }

    @Override
    public void close() {
        //Do nothing now.
    }
}

• Leaderelector imp implements the ileaderlector interface
• addToLeaderLockQueue method detects that if the latch has been closed, a new one will be created again, and then the status of the latch will be detected. If there is no start, start will be called to participate in the election
• There are two main reasons for creating a closed latch: one is that the method call to the already closed latch will throw an exception; the other is that it will be elected as a leader by zk, but some leader conditions of the unsatisfied store will give up the leadership, that is, close

Summary

• The leader elector of storm nimbus is mainly based on the leader latch of zookeeper recipes
• storm nimbus has customized the LeaderLatchListener to verify the nimbus after it becomes a leader. You need to have all active topologies and all dependencies locally, otherwise you will give up the leadership

doc

• Highly Available Nimbus Design