opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/RaftActor.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  * Copyright (c) 2015 Brocade Communications Systems, Inc. and others.  All rights reserved.
   4  *
   5  * This program and the accompanying materials are made available under the
   6  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   7  * and is available at http://www.eclipse.org/legal/epl-v10.html
   8  */
   9
  10 package org.opendaylight.controller.cluster.raft;
  11
  12 import akka.actor.ActorRef;
  13 import akka.actor.ActorSelection;
  14 import akka.actor.PoisonPill;
  15 import com.google.common.annotations.VisibleForTesting;
  16 import com.google.common.base.Optional;
  17 import com.google.common.base.Preconditions;
  18 import com.google.common.base.Verify;
  19 import com.google.common.collect.Lists;
  20 import java.util.Collection;
  21 import java.util.HashMap;
  22 import java.util.List;
  23 import java.util.Map;
  24 import java.util.Objects;
  25 import java.util.concurrent.TimeUnit;
  26 import javax.annotation.Nonnull;
  27 import javax.annotation.Nullable;
  28 import org.apache.commons.lang3.time.DurationFormatUtils;
  29 import org.opendaylight.controller.cluster.DataPersistenceProvider;
  30 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
  31 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
  32 import org.opendaylight.controller.cluster.PersistentDataProvider;
  33 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
  34 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
  35 import org.opendaylight.controller.cluster.notifications.RoleChanged;
  36 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  37 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
  38 import org.opendaylight.controller.cluster.raft.base.messages.InitiateCaptureSnapshot;
  39 import org.opendaylight.controller.cluster.raft.base.messages.LeaderTransitioning;
  40 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  41 import org.opendaylight.controller.cluster.raft.base.messages.SwitchBehavior;
  42 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
  43 import org.opendaylight.controller.cluster.raft.behaviors.AbstractRaftActorBehavior;
  44 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  45 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  46 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  47 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  48 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
  49 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
  50 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
  51 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
  52 import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
  53 import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
  54 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  55 import org.opendaylight.yangtools.concepts.Identifier;
  56 import org.opendaylight.yangtools.concepts.Immutable;
  57
  58 /**
  59  * RaftActor encapsulates a state machine that needs to be kept synchronized
  60  * in a cluster. It implements the RAFT algorithm as described in the paper
  61  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  62  * In Search of an Understandable Consensus Algorithm</a>
  63  *
  64  * <p>
  65  * RaftActor has 3 states and each state has a certain behavior associated
  66  * with it. A Raft actor can behave as,
  67  * <ul>
  68  * <li> A Leader </li>
  69  * <li> A Follower (or) </li>
  70  * <li> A Candidate </li>
  71  * </ul>
  72  *
  73  * <p>
  74  * A RaftActor MUST be a Leader in order to accept requests from clients to
  75  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  76  * a Leader it is also responsible for ensuring that all followers ultimately
  77  * have the same log and therefore the same state machine as itself.
  78  *
  79  * <p>
  80  * The current behavior of a RaftActor determines how election for leadership
  81  * is initiated and how peer RaftActors react to request for votes.
  82  *
  83  * <p>
  84  * Each RaftActor also needs to know the current election term. It uses this
  85  * information for a couple of things. One is to simply figure out who it
  86  * voted for in the last election. Another is to figure out if the message
  87  * it received to update it's state is stale.
  88  *
  89  * <p>
  90  * The RaftActor uses akka-persistence to store it's replicated log.
  91  * Furthermore through it's behaviors a Raft Actor determines
  92  * <ul>
  93  * <li> when a log entry should be persisted </li>
  94  * <li> when a log entry should be applied to the state machine (and) </li>
  95  * <li> when a snapshot should be saved </li>
  96  * </ul>
  97  */
  98 public abstract class RaftActor extends AbstractUntypedPersistentActor {
  99
 100     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
 101
 102     /**
 103      * This context should NOT be passed directly to any other actor it is
 104      * only to be consumed by the RaftActorBehaviors.
 105      */
 106     private final RaftActorContextImpl context;
 107
 108     private final DelegatingPersistentDataProvider delegatingPersistenceProvider;
 109
 110     private final PersistentDataProvider persistentProvider;
 111
 112     private final BehaviorStateTracker behaviorStateTracker = new BehaviorStateTracker();
 113
 114     private RaftActorRecoverySupport raftRecovery;
 115
 116     private RaftActorSnapshotMessageSupport snapshotSupport;
 117
 118     private RaftActorServerConfigurationSupport serverConfigurationSupport;
 119
 120     private RaftActorLeadershipTransferCohort leadershipTransferInProgress;
 121
 122     private boolean shuttingDown;
 123
 124     protected RaftActor(String id, Map<String, String> peerAddresses,
 125          Optional<ConfigParams> configParams, short payloadVersion) {
 126
 127         persistentProvider = new PersistentDataProvider(this);
 128         delegatingPersistenceProvider = new RaftActorDelegatingPersistentDataProvider(null, persistentProvider);
 129
 130         context = new RaftActorContextImpl(this.getSelf(),
 131             this.getContext(), id, new ElectionTermImpl(persistentProvider, id, LOG),
 132             -1, -1, peerAddresses,
 133             configParams.isPresent() ? configParams.get() : new DefaultConfigParamsImpl(),
 134             delegatingPersistenceProvider, LOG);
 135
 136         context.setPayloadVersion(payloadVersion);
 137         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context));
 138     }
 139
 140     @Override
 141     public void preStart() throws Exception {
 142         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
 143                 context.getConfigParams().getJournalRecoveryLogBatchSize());
 144
 145         super.preStart();
 146
 147         snapshotSupport = newRaftActorSnapshotMessageSupport();
 148         serverConfigurationSupport = new RaftActorServerConfigurationSupport(this);
 149     }
 150
 151     @Override
 152     public void postStop() {
 153         context.close();
 154         super.postStop();
 155     }
 156
 157     @Override
 158     protected void handleRecover(Object message) {
 159         if (raftRecovery == null) {
 160             raftRecovery = newRaftActorRecoverySupport();
 161         }
 162
 163         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message, persistentProvider);
 164         if (recoveryComplete) {
 165             onRecoveryComplete();
 166
 167             initializeBehavior();
 168
 169             raftRecovery = null;
 170         }
 171     }
 172
 173     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
 174         return new RaftActorRecoverySupport(context, getRaftActorRecoveryCohort());
 175     }
 176
 177     @VisibleForTesting
 178     void initializeBehavior() {
 179         changeCurrentBehavior(new Follower(context));
 180     }
 181
 182     @VisibleForTesting
 183     @SuppressWarnings("checkstyle:IllegalCatch")
 184     protected void changeCurrentBehavior(RaftActorBehavior newBehavior) {
 185         final RaftActorBehavior currentBehavior = getCurrentBehavior();
 186         if (currentBehavior != null) {
 187             try {
 188                 currentBehavior.close();
 189             } catch (Exception e) {
 190                 LOG.warn("{}: Error closing behavior {}", persistence(), currentBehavior, e);
 191             }
 192         }
 193
 194         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
 195         setCurrentBehavior(newBehavior);
 196         handleBehaviorChange(state, newBehavior);
 197     }
 198
 199     /**
 200      * Method exposed for subclasses to plug-in their logic. This method is invoked by {@link #handleCommand(Object)}
 201      * for messages which are not handled by this class. Subclasses overriding this class should fall back to this
 202      * implementation for messages which they do not handle
 203      *
 204      * @param message Incoming command message
 205      */
 206     protected void handleNonRaftCommand(final Object message) {
 207         unhandled(message);
 208     }
 209
 210     /**
 211      * Handles a message.
 212      *
 213      * @deprecated This method is not final for testing purposes. DO NOT OVERRIDE IT, override
 214      * {@link #handleNonRaftCommand(Object)} instead.
 215      */
 216     @Deprecated
 217     @Override
 218     // FIXME: make this method final once our unit tests do not need to override it
 219     protected void handleCommand(final Object message) {
 220         if (serverConfigurationSupport.handleMessage(message, getSender())) {
 221             return;
 222         }
 223         if (snapshotSupport.handleSnapshotMessage(message, getSender())) {
 224             return;
 225         }
 226
 227         if (message instanceof ApplyState) {
 228             ApplyState applyState = (ApplyState) message;
 229
 230             long startTime = System.nanoTime();
 231
 232             if (LOG.isDebugEnabled()) {
 233                 LOG.debug("{}: Applying state for log index {} data {}",
 234                     persistenceId(), applyState.getReplicatedLogEntry().getIndex(),
 235                     applyState.getReplicatedLogEntry().getData());
 236             }
 237
 238             if (!(applyState.getReplicatedLogEntry().getData() instanceof NoopPayload)) {
 239                 applyState(applyState.getClientActor(), applyState.getIdentifier(),
 240                     applyState.getReplicatedLogEntry().getData());
 241             }
 242
 243             long elapsedTime = System.nanoTime() - startTime;
 244             if (elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS) {
 245                 LOG.debug("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 246                         TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 247             }
 248
 249             if (!hasFollowers()) {
 250                 // for single node, the capture should happen after the apply state
 251                 // as we delete messages from the persistent journal which have made it to the snapshot
 252                 // capturing the snapshot before applying makes the persistent journal and snapshot out of sync
 253                 // and recovery shows data missing
 254                 context.getReplicatedLog().captureSnapshotIfReady(applyState.getReplicatedLogEntry());
 255
 256                 context.getSnapshotManager().trimLog(context.getLastApplied());
 257             }
 258
 259             // Send it to the current behavior - some behaviors like PreLeader need to be notified of ApplyState.
 260             possiblyHandleBehaviorMessage(message);
 261
 262         } else if (message instanceof ApplyJournalEntries) {
 263             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
 264             LOG.debug("{}: Persisting ApplyJournalEntries with index={}", persistenceId(), applyEntries.getToIndex());
 265
 266             persistence().persistAsync(applyEntries, NoopProcedure.instance());
 267
 268         } else if (message instanceof FindLeader) {
 269             getSender().tell(
 270                 new FindLeaderReply(getLeaderAddress()),
 271                 getSelf()
 272             );
 273         } else if (message instanceof GetOnDemandRaftState) {
 274             onGetOnDemandRaftStats();
 275         } else if (message instanceof InitiateCaptureSnapshot) {
 276             captureSnapshot();
 277         } else if (message instanceof SwitchBehavior) {
 278             switchBehavior((SwitchBehavior) message);
 279         } else if (message instanceof LeaderTransitioning) {
 280             onLeaderTransitioning();
 281         } else if (message instanceof Shutdown) {
 282             onShutDown();
 283         } else if (message instanceof Runnable) {
 284             ((Runnable)message).run();
 285         } else if (message instanceof NoopPayload) {
 286             persistData(null, null, (NoopPayload)message);
 287         } else if (!possiblyHandleBehaviorMessage(message)) {
 288             handleNonRaftCommand(message);
 289         }
 290     }
 291
 292     private boolean possiblyHandleBehaviorMessage(final Object message) {
 293         final RaftActorBehavior currentBehavior = getCurrentBehavior();
 294         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
 295
 296         // A behavior indicates that it processed the change by returning a reference to the next behavior
 297         // to be used. A null return indicates it has not processed the message and we should be passing it to
 298         // the subclass for handling.
 299         final RaftActorBehavior nextBehavior = currentBehavior.handleMessage(getSender(), message);
 300         if (nextBehavior != null) {
 301             switchBehavior(state, nextBehavior);
 302             return true;
 303         }
 304
 305         return false;
 306     }
 307
 308     private void initiateLeadershipTransfer(final RaftActorLeadershipTransferCohort.OnComplete onComplete) {
 309         LOG.debug("{}: Initiating leader transfer", persistenceId());
 310
 311         if (leadershipTransferInProgress == null) {
 312             leadershipTransferInProgress = new RaftActorLeadershipTransferCohort(this);
 313             leadershipTransferInProgress.addOnComplete(new RaftActorLeadershipTransferCohort.OnComplete() {
 314                 @Override
 315                 public void onSuccess(ActorRef raftActorRef) {
 316                     leadershipTransferInProgress = null;
 317                 }
 318
 319                 @Override
 320                 public void onFailure(ActorRef raftActorRef) {
 321                     leadershipTransferInProgress = null;
 322                 }
 323             });
 324
 325             leadershipTransferInProgress.addOnComplete(onComplete);
 326             leadershipTransferInProgress.init();
 327         } else {
 328             LOG.debug("{}: prior leader transfer in progress - adding callback", persistenceId());
 329             leadershipTransferInProgress.addOnComplete(onComplete);
 330         }
 331     }
 332
 333     private void onShutDown() {
 334         LOG.debug("{}: onShutDown", persistenceId());
 335
 336         if (shuttingDown) {
 337             return;
 338         }
 339
 340         shuttingDown = true;
 341
 342         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 343         if (currentBehavior.state() != RaftState.Leader) {
 344             // For non-leaders shutdown is a no-op
 345             self().tell(PoisonPill.getInstance(), self());
 346             return;
 347         }
 348
 349         if (context.hasFollowers()) {
 350             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 351                 @Override
 352                 public void onSuccess(ActorRef raftActorRef) {
 353                     LOG.debug("{}: leader transfer succeeded - sending PoisonPill", persistenceId());
 354                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 355                 }
 356
 357                 @Override
 358                 public void onFailure(ActorRef raftActorRef) {
 359                     LOG.debug("{}: leader transfer failed - sending PoisonPill", persistenceId());
 360                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 361                 }
 362             });
 363         } else {
 364             pauseLeader(new TimedRunnable(context.getConfigParams().getElectionTimeOutInterval(), this) {
 365                 @Override
 366                 protected void doRun() {
 367                     self().tell(PoisonPill.getInstance(), self());
 368                 }
 369
 370                 @Override
 371                 protected void doCancel() {
 372                     self().tell(PoisonPill.getInstance(), self());
 373                 }
 374             });
 375         }
 376     }
 377
 378     private void onLeaderTransitioning() {
 379         LOG.debug("{}: onLeaderTransitioning", persistenceId());
 380         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 381         if (getRaftState() == RaftState.Follower && roleChangeNotifier.isPresent()) {
 382             roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), null,
 383                 getCurrentBehavior().getLeaderPayloadVersion()), getSelf());
 384         }
 385     }
 386
 387     private void switchBehavior(SwitchBehavior message) {
 388         if (!getRaftActorContext().getRaftPolicy().automaticElectionsEnabled()) {
 389             RaftState newState = message.getNewState();
 390             if ( newState == RaftState.Leader || newState == RaftState.Follower) {
 391                 switchBehavior(behaviorStateTracker.capture(getCurrentBehavior()),
 392                     AbstractRaftActorBehavior.createBehavior(context, message.getNewState()));
 393                 getRaftActorContext().getTermInformation().updateAndPersist(message.getNewTerm(), "");
 394             } else {
 395                 LOG.warn("Switching to behavior : {} - not supported", newState);
 396             }
 397         }
 398     }
 399
 400     private void switchBehavior(final BehaviorState oldBehaviorState, final RaftActorBehavior nextBehavior) {
 401         setCurrentBehavior(nextBehavior);
 402         handleBehaviorChange(oldBehaviorState, nextBehavior);
 403     }
 404
 405     @VisibleForTesting
 406     RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
 407         return new RaftActorSnapshotMessageSupport(context, getRaftActorSnapshotCohort());
 408     }
 409
 410     private void onGetOnDemandRaftStats() {
 411         // Debugging message to retrieve raft stats.
 412
 413         Map<String, String> peerAddresses = new HashMap<>();
 414         Map<String, Boolean> peerVotingStates = new HashMap<>();
 415         for (PeerInfo info: context.getPeers()) {
 416             peerVotingStates.put(info.getId(), info.isVoting());
 417             peerAddresses.put(info.getId(), info.getAddress() != null ? info.getAddress() : "");
 418         }
 419
 420         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 421         OnDemandRaftState.Builder builder = OnDemandRaftState.builder()
 422                 .commitIndex(context.getCommitIndex())
 423                 .currentTerm(context.getTermInformation().getCurrentTerm())
 424                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 425                 .inMemoryJournalLogSize(replicatedLog().size())
 426                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 427                 .lastApplied(context.getLastApplied())
 428                 .lastIndex(replicatedLog().lastIndex())
 429                 .lastTerm(replicatedLog().lastTerm())
 430                 .leader(getLeaderId())
 431                 .raftState(currentBehavior.state().toString())
 432                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 433                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 434                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 435                 .votedFor(context.getTermInformation().getVotedFor())
 436                 .isVoting(context.isVotingMember())
 437                 .peerAddresses(peerAddresses)
 438                 .peerVotingStates(peerVotingStates)
 439                 .customRaftPolicyClassName(context.getConfigParams().getCustomRaftPolicyImplementationClass());
 440
 441         ReplicatedLogEntry lastLogEntry = replicatedLog().last();
 442         if (lastLogEntry != null) {
 443             builder.lastLogIndex(lastLogEntry.getIndex());
 444             builder.lastLogTerm(lastLogEntry.getTerm());
 445         }
 446
 447         if (getCurrentBehavior() instanceof AbstractLeader) {
 448             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
 449             Collection<String> followerIds = leader.getFollowerIds();
 450             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
 451             for (String id: followerIds) {
 452                 final FollowerLogInformation info = leader.getFollower(id);
 453                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
 454                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity()),
 455                         context.getPeerInfo(info.getId()).isVoting()));
 456             }
 457
 458             builder.followerInfoList(followerInfoList);
 459         }
 460
 461         sender().tell(builder.build(), self());
 462
 463     }
 464
 465     private void handleBehaviorChange(BehaviorState oldBehaviorState, RaftActorBehavior currentBehavior) {
 466         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 467
 468         if (oldBehavior != currentBehavior) {
 469             onStateChanged();
 470         }
 471
 472         String lastLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastLeaderId();
 473         String lastValidLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastValidLeaderId();
 474         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 475
 476         // it can happen that the state has not changed but the leader has changed.
 477         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 478         if (!Objects.equals(lastLeaderId, currentBehavior.getLeaderId())
 479                 || oldBehaviorState.getLeaderPayloadVersion() != currentBehavior.getLeaderPayloadVersion()) {
 480             if (roleChangeNotifier.isPresent()) {
 481                 roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), currentBehavior.getLeaderId(),
 482                         currentBehavior.getLeaderPayloadVersion()), getSelf());
 483             }
 484
 485             onLeaderChanged(lastValidLeaderId, currentBehavior.getLeaderId());
 486
 487             if (leadershipTransferInProgress != null) {
 488                 leadershipTransferInProgress.onNewLeader(currentBehavior.getLeaderId());
 489             }
 490
 491             serverConfigurationSupport.onNewLeader(currentBehavior.getLeaderId());
 492         }
 493
 494         if (roleChangeNotifier.isPresent()
 495                 && (oldBehavior == null || oldBehavior.state() != currentBehavior.state())) {
 496             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 497                     currentBehavior.state().name()), getSelf());
 498         }
 499     }
 500
 501     protected LeaderStateChanged newLeaderStateChanged(String memberId, String leaderId, short leaderPayloadVersion) {
 502         return new LeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
 503     }
 504
 505     @Override
 506     public long snapshotSequenceNr() {
 507         // When we do a snapshot capture, we also capture and save the sequence-number of the persistent journal,
 508         // so that we can delete the persistent journal based on the saved sequence-number
 509         // However , when akka replays the journal during recovery, it replays it from the sequence number when the
 510         // snapshot was saved and not the number we saved. We would want to override it , by asking akka to use the
 511         // last-sequence number known to us.
 512         return context.getSnapshotManager().getLastSequenceNumber();
 513     }
 514
 515     /**
 516      * When a derived RaftActor needs to persist something it must call
 517      * persistData.
 518      */
 519     protected final void persistData(final ActorRef clientActor, final Identifier identifier, final Payload data) {
 520
 521         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 522             context.getReplicatedLog().lastIndex() + 1,
 523             context.getTermInformation().getCurrentTerm(), data);
 524         replicatedLogEntry.setPersistencePending(true);
 525
 526         LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 527
 528         final RaftActorContext raftContext = getRaftActorContext();
 529
 530         boolean wasAppended = replicatedLog().appendAndPersist(replicatedLogEntry, persistedLogEntry -> {
 531             // Clear the persistence pending flag in the log entry.
 532             persistedLogEntry.setPersistencePending(false);
 533
 534             if (!hasFollowers()) {
 535                 // Increment the Commit Index and the Last Applied values
 536                 raftContext.setCommitIndex(persistedLogEntry.getIndex());
 537                 raftContext.setLastApplied(persistedLogEntry.getIndex());
 538
 539                 // Apply the state immediately.
 540                 self().tell(new ApplyState(clientActor, identifier, persistedLogEntry), self());
 541
 542                 // Send a ApplyJournalEntries message so that we write the fact that we applied
 543                 // the state to durable storage
 544                 self().tell(new ApplyJournalEntries(persistedLogEntry.getIndex()), self());
 545
 546             } else {
 547                 context.getReplicatedLog().captureSnapshotIfReady(replicatedLogEntry);
 548
 549                 // Local persistence is complete so send the CheckConsensusReached message to the behavior (which
 550                 // normally should still be the leader) to check if consensus has now been reached in conjunction with
 551                 // follower replication.
 552                 getCurrentBehavior().handleMessage(getSelf(), CheckConsensusReached.INSTANCE);
 553             }
 554         }, true);
 555
 556         if (wasAppended && hasFollowers()) {
 557             // Send log entry for replication.
 558             getCurrentBehavior().handleMessage(getSelf(), new Replicate(clientActor, identifier, replicatedLogEntry));
 559         }
 560     }
 561
 562     private ReplicatedLog replicatedLog() {
 563         return context.getReplicatedLog();
 564     }
 565
 566     protected String getId() {
 567         return context.getId();
 568     }
 569
 570     @VisibleForTesting
 571     void setCurrentBehavior(RaftActorBehavior behavior) {
 572         context.setCurrentBehavior(behavior);
 573     }
 574
 575     protected RaftActorBehavior getCurrentBehavior() {
 576         return context.getCurrentBehavior();
 577     }
 578
 579     /**
 580      * Derived actors can call the isLeader method to check if the current
 581      * RaftActor is the Leader or not.
 582      *
 583      * @return true it this RaftActor is a Leader false otherwise
 584      */
 585     protected boolean isLeader() {
 586         return context.getId().equals(getCurrentBehavior().getLeaderId());
 587     }
 588
 589     protected final boolean isLeaderActive() {
 590         return getRaftState() != RaftState.IsolatedLeader && getRaftState() != RaftState.PreLeader
 591                 && !shuttingDown && !isLeadershipTransferInProgress();
 592     }
 593
 594     private boolean isLeadershipTransferInProgress() {
 595         return leadershipTransferInProgress != null && leadershipTransferInProgress.isTransferring();
 596     }
 597
 598     /**
 599      * Derived actor can call getLeader if they need a reference to the Leader.
 600      * This would be useful for example in forwarding a request to an actor
 601      * which is the leader
 602      *
 603      * @return A reference to the leader if known, null otherwise
 604      */
 605     public ActorSelection getLeader() {
 606         String leaderAddress = getLeaderAddress();
 607
 608         if (leaderAddress == null) {
 609             return null;
 610         }
 611
 612         return context.actorSelection(leaderAddress);
 613     }
 614
 615     /**
 616      * Returns the id of the current leader.
 617      *
 618      * @return the current leader's id
 619      */
 620     protected final String getLeaderId() {
 621         return getCurrentBehavior().getLeaderId();
 622     }
 623
 624     @VisibleForTesting
 625     protected final RaftState getRaftState() {
 626         return getCurrentBehavior().state();
 627     }
 628
 629     protected Long getCurrentTerm() {
 630         return context.getTermInformation().getCurrentTerm();
 631     }
 632
 633     protected RaftActorContext getRaftActorContext() {
 634         return context;
 635     }
 636
 637     protected void updateConfigParams(ConfigParams configParams) {
 638
 639         // obtain the RaftPolicy for oldConfigParams and the updated one.
 640         String oldRaftPolicy = context.getConfigParams().getCustomRaftPolicyImplementationClass();
 641         String newRaftPolicy = configParams.getCustomRaftPolicyImplementationClass();
 642
 643         LOG.debug("{}: RaftPolicy used with prev.config {}, RaftPolicy used with newConfig {}", persistenceId(),
 644             oldRaftPolicy, newRaftPolicy);
 645         context.setConfigParams(configParams);
 646         if (!Objects.equals(oldRaftPolicy, newRaftPolicy)) {
 647             // The RaftPolicy was modified. If the current behavior is Follower then re-initialize to Follower
 648             // but transfer the previous leaderId so it doesn't immediately try to schedule an election. This
 649             // avoids potential disruption. Otherwise, switch to Follower normally.
 650             RaftActorBehavior behavior = getCurrentBehavior();
 651             if (behavior != null && behavior.state() == RaftState.Follower) {
 652                 String previousLeaderId = behavior.getLeaderId();
 653                 short previousLeaderPayloadVersion = behavior.getLeaderPayloadVersion();
 654
 655                 LOG.debug("{}: Re-initializing to Follower with previous leaderId {}", persistenceId(),
 656                         previousLeaderId);
 657
 658                 changeCurrentBehavior(new Follower(context, previousLeaderId, previousLeaderPayloadVersion));
 659             } else {
 660                 initializeBehavior();
 661             }
 662         }
 663     }
 664
 665     public final DataPersistenceProvider persistence() {
 666         return delegatingPersistenceProvider.getDelegate();
 667     }
 668
 669     public void setPersistence(DataPersistenceProvider provider) {
 670         delegatingPersistenceProvider.setDelegate(provider);
 671     }
 672
 673     protected void setPersistence(boolean persistent) {
 674         DataPersistenceProvider currentPersistence = persistence();
 675         if (persistent && (currentPersistence == null || !currentPersistence.isRecoveryApplicable())) {
 676             setPersistence(new PersistentDataProvider(this));
 677
 678             if (getCurrentBehavior() != null) {
 679                 LOG.info("{}: Persistence has been enabled - capturing snapshot", persistenceId());
 680                 captureSnapshot();
 681             }
 682         } else if (!persistent && (currentPersistence == null || currentPersistence.isRecoveryApplicable())) {
 683             setPersistence(new NonPersistentDataProvider() {
 684                 /**
 685                  * The way snapshotting works is,
 686                  * <ol>
 687                  * <li> RaftActor calls createSnapshot on the Shard
 688                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 689                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 690                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 691                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 692                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 693                  * </ol>
 694                  */
 695                 @Override
 696                 public void saveSnapshot(Object object) {
 697                     // Make saving Snapshot successful
 698                     // Committing the snapshot here would end up calling commit in the creating state which would
 699                     // be a state violation. That's why now we send a message to commit the snapshot.
 700                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
 701                 }
 702             });
 703         }
 704     }
 705
 706     /**
 707      * setPeerAddress sets the address of a known peer at a later time.
 708      *
 709      * <p>
 710      * This is to account for situations where a we know that a peer
 711      * exists but we do not know an address up-front. This may also be used in
 712      * situations where a known peer starts off in a different location and we
 713      * need to change it's address
 714      *
 715      * <p>
 716      * Note that if the peerId does not match the list of peers passed to
 717      * this actor during construction an IllegalStateException will be thrown.
 718      */
 719     protected void setPeerAddress(String peerId, String peerAddress) {
 720         context.setPeerAddress(peerId, peerAddress);
 721     }
 722
 723     /**
 724      * The applyState method will be called by the RaftActor when some data
 725      * needs to be applied to the actor's state.
 726      *
 727      * @param clientActor A reference to the client who sent this message. This
 728      *                    is the same reference that was passed to persistData
 729      *                    by the derived actor. clientActor may be null when
 730      *                    the RaftActor is behaving as a follower or during
 731      *                    recovery.
 732      * @param identifier  The identifier of the persisted data. This is also
 733      *                    the same identifier that was passed to persistData by
 734      *                    the derived actor. identifier may be null when
 735      *                    the RaftActor is behaving as a follower or during
 736      *                    recovery
 737      * @param data        A piece of data that was persisted by the persistData call.
 738      *                    This should NEVER be null.
 739      */
 740     protected abstract void applyState(ActorRef clientActor, Identifier identifier, Object data);
 741
 742     /**
 743      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
 744      */
 745     @Nonnull
 746     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
 747
 748     /**
 749      * This method is called when recovery is complete.
 750      */
 751     protected abstract void onRecoveryComplete();
 752
 753     /**
 754      * Returns the RaftActorSnapshotCohort to participate in persistence recovery.
 755      */
 756     @Nonnull
 757     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
 758
 759     /**
 760      * This method will be called by the RaftActor when the state of the
 761      * RaftActor changes. The derived actor can then use methods like
 762      * isLeader or getLeader to do something useful
 763      */
 764     protected abstract void onStateChanged();
 765
 766     /**
 767      * Notifier Actor for this RaftActor to notify when a role change happens.
 768      *
 769      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 770      */
 771     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 772
 773     /**
 774      * This method is called prior to operations such as leadership transfer and actor shutdown when the leader
 775      * must pause or stop its duties. This method allows derived classes to gracefully pause or finish current
 776      * work prior to performing the operation. On completion of any work, the run method must be called on the
 777      * given Runnable to proceed with the given operation. <b>Important:</b> the run method must be called on
 778      * this actor's thread dispatcher as as it modifies internal state.
 779      *
 780      * <p>
 781      * The default implementation immediately runs the operation.
 782      *
 783      * @param operation the operation to run
 784      */
 785     protected void pauseLeader(Runnable operation) {
 786         operation.run();
 787     }
 788
 789     protected void onLeaderChanged(String oldLeader, String newLeader) {
 790     }
 791
 792     private String getLeaderAddress() {
 793         if (isLeader()) {
 794             return getSelf().path().toString();
 795         }
 796         String leaderId = getLeaderId();
 797         if (leaderId == null) {
 798             return null;
 799         }
 800         String peerAddress = context.getPeerAddress(leaderId);
 801         LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}", persistenceId(), leaderId, peerAddress);
 802
 803         return peerAddress;
 804     }
 805
 806     protected boolean hasFollowers() {
 807         return getRaftActorContext().hasFollowers();
 808     }
 809
 810     private void captureSnapshot() {
 811         SnapshotManager snapshotManager = context.getSnapshotManager();
 812
 813         if (!snapshotManager.isCapturing()) {
 814             final long idx = getCurrentBehavior().getReplicatedToAllIndex();
 815             LOG.debug("Take a snapshot of current state. lastReplicatedLog is {} and replicatedToAllIndex is {}",
 816                 replicatedLog().last(), idx);
 817
 818             snapshotManager.capture(replicatedLog().last(), idx);
 819         }
 820     }
 821
 822     /**
 823      * Switch this member to non-voting status. This is a no-op for all behaviors except when we are the leader,
 824      * in which case we need to step down.
 825      */
 826     void becomeNonVoting() {
 827         if (isLeader()) {
 828             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 829                 @Override
 830                 public void onSuccess(ActorRef raftActorRef) {
 831                     LOG.debug("{}: leader transfer succeeded after change to non-voting", persistenceId());
 832                     ensureFollowerState();
 833                 }
 834
 835                 @Override
 836                 public void onFailure(ActorRef raftActorRef) {
 837                     LOG.debug("{}: leader transfer failed after change to non-voting", persistenceId());
 838                     ensureFollowerState();
 839                 }
 840
 841                 private void ensureFollowerState() {
 842                     // Whether or not leadership transfer succeeded, we have to step down as leader and
 843                     // switch to Follower so ensure that.
 844                     if (getRaftState() != RaftState.Follower) {
 845                         initializeBehavior();
 846                     }
 847                 }
 848             });
 849         }
 850     }
 851
 852     /**
 853      * A point-in-time capture of {@link RaftActorBehavior} state critical for transitioning between behaviors.
 854      */
 855     private abstract static class BehaviorState implements Immutable {
 856         @Nullable abstract RaftActorBehavior getBehavior();
 857
 858         @Nullable abstract String getLastValidLeaderId();
 859
 860         @Nullable abstract String getLastLeaderId();
 861
 862         @Nullable abstract short getLeaderPayloadVersion();
 863     }
 864
 865     /**
 866      * A {@link BehaviorState} corresponding to non-null {@link RaftActorBehavior} state.
 867      */
 868     private static final class SimpleBehaviorState extends BehaviorState {
 869         private final RaftActorBehavior behavior;
 870         private final String lastValidLeaderId;
 871         private final String lastLeaderId;
 872         private final short leaderPayloadVersion;
 873
 874         SimpleBehaviorState(final String lastValidLeaderId, final String lastLeaderId,
 875                 final RaftActorBehavior behavior) {
 876             this.lastValidLeaderId = lastValidLeaderId;
 877             this.lastLeaderId = lastLeaderId;
 878             this.behavior = Preconditions.checkNotNull(behavior);
 879             this.leaderPayloadVersion = behavior.getLeaderPayloadVersion();
 880         }
 881
 882         @Override
 883         RaftActorBehavior getBehavior() {
 884             return behavior;
 885         }
 886
 887         @Override
 888         String getLastValidLeaderId() {
 889             return lastValidLeaderId;
 890         }
 891
 892         @Override
 893         short getLeaderPayloadVersion() {
 894             return leaderPayloadVersion;
 895         }
 896
 897         @Override
 898         String getLastLeaderId() {
 899             return lastLeaderId;
 900         }
 901     }
 902
 903     /**
 904      * Class tracking behavior-related information, which we need to keep around and pass across behavior switches.
 905      * An instance is created for each RaftActor. It has two functions:
 906      * - it keeps track of the last leader ID we have encountered since we have been created
 907      * - it creates state capture needed to transition from one behavior to the next
 908      */
 909     private static final class BehaviorStateTracker {
 910         /**
 911          * A {@link BehaviorState} corresponding to null {@link RaftActorBehavior} state. Since null behavior is only
 912          * allowed before we receive the first message, we know the leader ID to be null.
 913          */
 914         private static final BehaviorState NULL_BEHAVIOR_STATE = new BehaviorState() {
 915             @Override
 916             RaftActorBehavior getBehavior() {
 917                 return null;
 918             }
 919
 920             @Override
 921             String getLastValidLeaderId() {
 922                 return null;
 923             }
 924
 925             @Override
 926             short getLeaderPayloadVersion() {
 927                 return -1;
 928             }
 929
 930             @Override
 931             String getLastLeaderId() {
 932                 return null;
 933             }
 934         };
 935
 936         private String lastValidLeaderId;
 937         private String lastLeaderId;
 938
 939         BehaviorState capture(final RaftActorBehavior behavior) {
 940             if (behavior == null) {
 941                 Verify.verify(lastValidLeaderId == null, "Null behavior with non-null last leader");
 942                 return NULL_BEHAVIOR_STATE;
 943             }
 944
 945             lastLeaderId = behavior.getLeaderId();
 946             if (lastLeaderId != null) {
 947                 lastValidLeaderId = lastLeaderId;
 948             }
 949
 950             return new SimpleBehaviorState(lastValidLeaderId, lastLeaderId, behavior);
 951         }
 952     }
 953
 954 }