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 akka.actor.Status;
  16 import com.google.common.annotations.VisibleForTesting;
  17 import com.google.common.base.Optional;
  18 import com.google.common.base.Preconditions;
  19 import com.google.common.base.Verify;
  20 import com.google.common.collect.Lists;
  21 import java.util.Collection;
  22 import java.util.HashMap;
  23 import java.util.List;
  24 import java.util.Map;
  25 import java.util.Objects;
  26 import java.util.concurrent.TimeUnit;
  27 import javax.annotation.Nonnull;
  28 import javax.annotation.Nullable;
  29 import org.apache.commons.lang3.time.DurationFormatUtils;
  30 import org.opendaylight.controller.cluster.DataPersistenceProvider;
  31 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
  32 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
  33 import org.opendaylight.controller.cluster.PersistentDataProvider;
  34 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
  35 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
  36 import org.opendaylight.controller.cluster.notifications.RoleChanged;
  37 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  38 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
  39 import org.opendaylight.controller.cluster.raft.base.messages.InitiateCaptureSnapshot;
  40 import org.opendaylight.controller.cluster.raft.base.messages.LeaderTransitioning;
  41 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  42 import org.opendaylight.controller.cluster.raft.base.messages.SwitchBehavior;
  43 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
  44 import org.opendaylight.controller.cluster.raft.behaviors.AbstractRaftActorBehavior;
  45 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  46 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  47 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  48 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  49 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
  50 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
  51 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
  52 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
  53 import org.opendaylight.controller.cluster.raft.messages.RequestLeadership;
  54 import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
  55 import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
  56 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  57 import org.opendaylight.controller.cluster.raft.persisted.SimpleReplicatedLogEntry;
  58 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  59 import org.opendaylight.yangtools.concepts.Identifier;
  60 import org.opendaylight.yangtools.concepts.Immutable;
  61
  62 /**
  63  * RaftActor encapsulates a state machine that needs to be kept synchronized
  64  * in a cluster. It implements the RAFT algorithm as described in the paper
  65  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  66  * In Search of an Understandable Consensus Algorithm</a>
  67  *
  68  * <p>
  69  * RaftActor has 3 states and each state has a certain behavior associated
  70  * with it. A Raft actor can behave as,
  71  * <ul>
  72  * <li> A Leader </li>
  73  * <li> A Follower (or) </li>
  74  * <li> A Candidate </li>
  75  * </ul>
  76  *
  77  * <p>
  78  * A RaftActor MUST be a Leader in order to accept requests from clients to
  79  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  80  * a Leader it is also responsible for ensuring that all followers ultimately
  81  * have the same log and therefore the same state machine as itself.
  82  *
  83  * <p>
  84  * The current behavior of a RaftActor determines how election for leadership
  85  * is initiated and how peer RaftActors react to request for votes.
  86  *
  87  * <p>
  88  * Each RaftActor also needs to know the current election term. It uses this
  89  * information for a couple of things. One is to simply figure out who it
  90  * voted for in the last election. Another is to figure out if the message
  91  * it received to update it's state is stale.
  92  *
  93  * <p>
  94  * The RaftActor uses akka-persistence to store it's replicated log.
  95  * Furthermore through it's behaviors a Raft Actor determines
  96  * <ul>
  97  * <li> when a log entry should be persisted </li>
  98  * <li> when a log entry should be applied to the state machine (and) </li>
  99  * <li> when a snapshot should be saved </li>
 100  * </ul>
 101  */
 102 public abstract class RaftActor extends AbstractUntypedPersistentActor {
 103
 104     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
 105
 106     /**
 107      * This context should NOT be passed directly to any other actor it is
 108      * only to be consumed by the RaftActorBehaviors.
 109      */
 110     private final RaftActorContextImpl context;
 111
 112     private final DelegatingPersistentDataProvider delegatingPersistenceProvider;
 113
 114     private final PersistentDataProvider persistentProvider;
 115
 116     private final BehaviorStateTracker behaviorStateTracker = new BehaviorStateTracker();
 117
 118     private RaftActorRecoverySupport raftRecovery;
 119
 120     private RaftActorSnapshotMessageSupport snapshotSupport;
 121
 122     private RaftActorServerConfigurationSupport serverConfigurationSupport;
 123
 124     private boolean shuttingDown;
 125
 126     protected RaftActor(final String id, final Map<String, String> peerAddresses,
 127          final Optional<ConfigParams> configParams, final short payloadVersion) {
 128
 129         persistentProvider = new PersistentDataProvider(this);
 130         delegatingPersistenceProvider = new RaftActorDelegatingPersistentDataProvider(null, persistentProvider);
 131
 132         context = new RaftActorContextImpl(this.getSelf(),
 133             this.getContext(), id, new ElectionTermImpl(persistentProvider, id, LOG),
 134             -1, -1, peerAddresses,
 135             configParams.isPresent() ? configParams.get() : new DefaultConfigParamsImpl(),
 136             delegatingPersistenceProvider, this::handleApplyState, LOG);
 137
 138         context.setPayloadVersion(payloadVersion);
 139         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context));
 140     }
 141
 142     @Override
 143     public void preStart() throws Exception {
 144         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
 145                 context.getConfigParams().getJournalRecoveryLogBatchSize());
 146
 147         super.preStart();
 148
 149         snapshotSupport = newRaftActorSnapshotMessageSupport();
 150         serverConfigurationSupport = new RaftActorServerConfigurationSupport(this);
 151     }
 152
 153     @Override
 154     public void postStop() {
 155         context.close();
 156         super.postStop();
 157     }
 158
 159     @Override
 160     protected void handleRecover(final Object message) {
 161         if (raftRecovery == null) {
 162             raftRecovery = newRaftActorRecoverySupport();
 163         }
 164
 165         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message, persistentProvider);
 166         if (recoveryComplete) {
 167             onRecoveryComplete();
 168
 169             initializeBehavior();
 170
 171             raftRecovery = null;
 172         }
 173     }
 174
 175     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
 176         return new RaftActorRecoverySupport(context, getRaftActorRecoveryCohort());
 177     }
 178
 179     @VisibleForTesting
 180     void initializeBehavior() {
 181         changeCurrentBehavior(new Follower(context));
 182     }
 183
 184     @VisibleForTesting
 185     @SuppressWarnings("checkstyle:IllegalCatch")
 186     protected void changeCurrentBehavior(final RaftActorBehavior newBehavior) {
 187         final RaftActorBehavior currentBehavior = getCurrentBehavior();
 188         if (currentBehavior != null) {
 189             try {
 190                 currentBehavior.close();
 191             } catch (Exception e) {
 192                 LOG.warn("{}: Error closing behavior {}", persistence(), currentBehavior, e);
 193             }
 194         }
 195
 196         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
 197         setCurrentBehavior(newBehavior);
 198         handleBehaviorChange(state, newBehavior);
 199     }
 200
 201     /**
 202      * Method exposed for subclasses to plug-in their logic. This method is invoked by {@link #handleCommand(Object)}
 203      * for messages which are not handled by this class. Subclasses overriding this class should fall back to this
 204      * implementation for messages which they do not handle
 205      *
 206      * @param message Incoming command message
 207      */
 208     protected void handleNonRaftCommand(final Object message) {
 209         unhandled(message);
 210     }
 211
 212     /**
 213      * Handles a message.
 214      *
 215      * @deprecated This method is not final for testing purposes. DO NOT OVERRIDE IT, override
 216      * {@link #handleNonRaftCommand(Object)} instead.
 217      */
 218     @Deprecated
 219     @Override
 220     // FIXME: make this method final once our unit tests do not need to override it
 221     protected void handleCommand(final Object message) {
 222         if (serverConfigurationSupport.handleMessage(message, getSender())) {
 223             return;
 224         }
 225         if (snapshotSupport.handleSnapshotMessage(message, getSender())) {
 226             return;
 227         }
 228         if (message instanceof ApplyState) {
 229             ApplyState applyState = (ApplyState) message;
 230
 231             if (!hasFollowers()) {
 232                 // for single node, the capture should happen after the apply state
 233                 // as we delete messages from the persistent journal which have made it to the snapshot
 234                 // capturing the snapshot before applying makes the persistent journal and snapshot out of sync
 235                 // and recovery shows data missing
 236                 context.getReplicatedLog().captureSnapshotIfReady(applyState.getReplicatedLogEntry());
 237
 238                 context.getSnapshotManager().trimLog(context.getLastApplied());
 239             }
 240
 241             possiblyHandleBehaviorMessage(message);
 242         } else if (message instanceof ApplyJournalEntries) {
 243             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
 244             LOG.debug("{}: Persisting ApplyJournalEntries with index={}", persistenceId(), applyEntries.getToIndex());
 245
 246             persistence().persistAsync(applyEntries, NoopProcedure.instance());
 247
 248         } else if (message instanceof FindLeader) {
 249             getSender().tell(
 250                 new FindLeaderReply(getLeaderAddress()),
 251                 getSelf()
 252             );
 253         } else if (message instanceof GetOnDemandRaftState) {
 254             onGetOnDemandRaftStats();
 255         } else if (message instanceof InitiateCaptureSnapshot) {
 256             captureSnapshot();
 257         } else if (message instanceof SwitchBehavior) {
 258             switchBehavior((SwitchBehavior) message);
 259         } else if (message instanceof LeaderTransitioning) {
 260             onLeaderTransitioning((LeaderTransitioning)message);
 261         } else if (message instanceof Shutdown) {
 262             onShutDown();
 263         } else if (message instanceof Runnable) {
 264             ((Runnable)message).run();
 265         } else if (message instanceof NoopPayload) {
 266             persistData(null, null, (NoopPayload) message, false);
 267         } else if (message instanceof RequestLeadership) {
 268             onRequestLeadership((RequestLeadership) message);
 269         } else if (!possiblyHandleBehaviorMessage(message)) {
 270             handleNonRaftCommand(message);
 271         }
 272     }
 273
 274     private void onRequestLeadership(final RequestLeadership message) {
 275         LOG.debug("{}: onRequestLeadership {}", persistenceId(), message);
 276         if (!isLeader()) {
 277             // non-leader cannot satisfy leadership request
 278             LOG.warn("{}: onRequestLeadership {} was sent to non-leader."
 279                     + " Current behavior: {}. Sending failure response",
 280                     persistenceId(), getCurrentBehavior().state());
 281             message.getReplyTo().tell(new LeadershipTransferFailedException("Cannot transfer leader to "
 282                     + message.getRequestedFollowerId()
 283                     + ". RequestLeadership message was sent to non-leader " + persistenceId()), getSelf());
 284             return;
 285         }
 286
 287         final String requestedFollowerId = message.getRequestedFollowerId();
 288         final ActorRef replyTo = message.getReplyTo();
 289         initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 290             @Override
 291             public void onSuccess(final ActorRef raftActorRef) {
 292                 // sanity check
 293                 if (!requestedFollowerId.equals(getLeaderId())) {
 294                     onFailure(raftActorRef);
 295                 }
 296
 297                 LOG.debug("{}: Leadership transferred successfully to {}", persistenceId(), requestedFollowerId);
 298                 replyTo.tell(new Status.Success(null), getSelf());
 299             }
 300
 301             @Override
 302             public void onFailure(final ActorRef raftActorRef) {
 303                 LOG.debug("{}: LeadershipTransfer request from {} failed", persistenceId(), requestedFollowerId);
 304                 replyTo.tell(new Status.Failure(
 305                         new LeadershipTransferFailedException(
 306                                 "Failed to transfer leadership to " + requestedFollowerId
 307                                         + ". Follower is not ready to become leader")),
 308                         getSelf());
 309             }
 310         }, message.getRequestedFollowerId(), RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
 311     }
 312
 313     private boolean possiblyHandleBehaviorMessage(final Object message) {
 314         final RaftActorBehavior currentBehavior = getCurrentBehavior();
 315         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
 316
 317         // A behavior indicates that it processed the change by returning a reference to the next behavior
 318         // to be used. A null return indicates it has not processed the message and we should be passing it to
 319         // the subclass for handling.
 320         final RaftActorBehavior nextBehavior = currentBehavior.handleMessage(getSender(), message);
 321         if (nextBehavior != null) {
 322             switchBehavior(state, nextBehavior);
 323             return true;
 324         }
 325
 326         return false;
 327     }
 328
 329     private void initiateLeadershipTransfer(final RaftActorLeadershipTransferCohort.OnComplete onComplete,
 330             @Nullable final String followerId, final long newLeaderTimeoutInMillis) {
 331         LOG.debug("{}: Initiating leader transfer", persistenceId());
 332
 333         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
 334         if (leadershipTransferInProgress == null) {
 335             leadershipTransferInProgress = new RaftActorLeadershipTransferCohort(this, followerId);
 336             leadershipTransferInProgress.setNewLeaderTimeoutInMillis(newLeaderTimeoutInMillis);
 337             leadershipTransferInProgress.addOnComplete(new RaftActorLeadershipTransferCohort.OnComplete() {
 338                 @Override
 339                 public void onSuccess(final ActorRef raftActorRef) {
 340                     context.setRaftActorLeadershipTransferCohort(null);
 341                 }
 342
 343                 @Override
 344                 public void onFailure(final ActorRef raftActorRef) {
 345                     context.setRaftActorLeadershipTransferCohort(null);
 346                 }
 347             });
 348
 349             leadershipTransferInProgress.addOnComplete(onComplete);
 350
 351             context.setRaftActorLeadershipTransferCohort(leadershipTransferInProgress);
 352             leadershipTransferInProgress.init();
 353
 354         } else {
 355             LOG.debug("{}: prior leader transfer in progress - adding callback", persistenceId());
 356             leadershipTransferInProgress.addOnComplete(onComplete);
 357         }
 358     }
 359
 360     private void onShutDown() {
 361         LOG.debug("{}: onShutDown", persistenceId());
 362
 363         if (shuttingDown) {
 364             return;
 365         }
 366
 367         shuttingDown = true;
 368
 369         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 370         switch (currentBehavior.state()) {
 371             case Leader:
 372             case PreLeader:
 373                 // Fall-through to more work
 374                 break;
 375             default:
 376                 // For non-leaders shutdown is a no-op
 377                 self().tell(PoisonPill.getInstance(), self());
 378                 return;
 379         }
 380
 381         if (context.hasFollowers()) {
 382             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 383                 @Override
 384                 public void onSuccess(final ActorRef raftActorRef) {
 385                     LOG.debug("{}: leader transfer succeeded - sending PoisonPill", persistenceId());
 386                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 387                 }
 388
 389                 @Override
 390                 public void onFailure(final ActorRef raftActorRef) {
 391                     LOG.debug("{}: leader transfer failed - sending PoisonPill", persistenceId());
 392                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 393                 }
 394             }, null, TimeUnit.MILLISECONDS.convert(2, TimeUnit.SECONDS));
 395         } else {
 396             pauseLeader(new TimedRunnable(context.getConfigParams().getElectionTimeOutInterval(), this) {
 397                 @Override
 398                 protected void doRun() {
 399                     self().tell(PoisonPill.getInstance(), self());
 400                 }
 401
 402                 @Override
 403                 protected void doCancel() {
 404                     self().tell(PoisonPill.getInstance(), self());
 405                 }
 406             });
 407         }
 408     }
 409
 410     private void onLeaderTransitioning(final LeaderTransitioning leaderTransitioning) {
 411         LOG.debug("{}: onLeaderTransitioning: {}", persistenceId(), leaderTransitioning);
 412         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 413         if (getRaftState() == RaftState.Follower && roleChangeNotifier.isPresent()
 414                 && leaderTransitioning.getLeaderId().equals(getCurrentBehavior().getLeaderId())) {
 415             roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), null,
 416                 getCurrentBehavior().getLeaderPayloadVersion()), getSelf());
 417         }
 418     }
 419
 420     private void switchBehavior(final SwitchBehavior message) {
 421         if (!getRaftActorContext().getRaftPolicy().automaticElectionsEnabled()) {
 422             RaftState newState = message.getNewState();
 423             if (newState == RaftState.Leader || newState == RaftState.Follower) {
 424                 getRaftActorContext().getTermInformation().updateAndPersist(message.getNewTerm(), "");
 425                 switchBehavior(behaviorStateTracker.capture(getCurrentBehavior()),
 426                     AbstractRaftActorBehavior.createBehavior(context, message.getNewState()));
 427             } else {
 428                 LOG.warn("Switching to behavior : {} - not supported", newState);
 429             }
 430         }
 431     }
 432
 433     private void switchBehavior(final BehaviorState oldBehaviorState, final RaftActorBehavior nextBehavior) {
 434         setCurrentBehavior(nextBehavior);
 435         handleBehaviorChange(oldBehaviorState, nextBehavior);
 436     }
 437
 438     @VisibleForTesting
 439     RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
 440         return new RaftActorSnapshotMessageSupport(context, getRaftActorSnapshotCohort());
 441     }
 442
 443     private void onGetOnDemandRaftStats() {
 444         // Debugging message to retrieve raft stats.
 445
 446         Map<String, String> peerAddresses = new HashMap<>();
 447         Map<String, Boolean> peerVotingStates = new HashMap<>();
 448         for (PeerInfo info: context.getPeers()) {
 449             peerVotingStates.put(info.getId(), info.isVoting());
 450             peerAddresses.put(info.getId(), info.getAddress() != null ? info.getAddress() : "");
 451         }
 452
 453         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 454         OnDemandRaftState.AbstractBuilder<?, ?> builder = newOnDemandRaftStateBuilder()
 455                 .commitIndex(context.getCommitIndex())
 456                 .currentTerm(context.getTermInformation().getCurrentTerm())
 457                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 458                 .inMemoryJournalLogSize(replicatedLog().size())
 459                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 460                 .lastApplied(context.getLastApplied())
 461                 .lastIndex(replicatedLog().lastIndex())
 462                 .lastTerm(replicatedLog().lastTerm())
 463                 .leader(getLeaderId())
 464                 .raftState(currentBehavior.state().toString())
 465                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 466                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 467                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 468                 .votedFor(context.getTermInformation().getVotedFor())
 469                 .isVoting(context.isVotingMember())
 470                 .peerAddresses(peerAddresses)
 471                 .peerVotingStates(peerVotingStates)
 472                 .customRaftPolicyClassName(context.getConfigParams().getCustomRaftPolicyImplementationClass());
 473
 474         ReplicatedLogEntry lastLogEntry = replicatedLog().last();
 475         if (lastLogEntry != null) {
 476             builder.lastLogIndex(lastLogEntry.getIndex());
 477             builder.lastLogTerm(lastLogEntry.getTerm());
 478         }
 479
 480         if (getCurrentBehavior() instanceof AbstractLeader) {
 481             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
 482             Collection<String> followerIds = leader.getFollowerIds();
 483             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
 484             for (String id: followerIds) {
 485                 final FollowerLogInformation info = leader.getFollower(id);
 486                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
 487                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity()),
 488                         context.getPeerInfo(info.getId()).isVoting()));
 489             }
 490
 491             builder.followerInfoList(followerInfoList);
 492         }
 493
 494         sender().tell(builder.build(), self());
 495
 496     }
 497
 498     protected OnDemandRaftState.AbstractBuilder<?, ?> newOnDemandRaftStateBuilder() {
 499         return OnDemandRaftState.builder();
 500     }
 501
 502     private void handleBehaviorChange(final BehaviorState oldBehaviorState, final RaftActorBehavior currentBehavior) {
 503         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 504
 505         if (oldBehavior != currentBehavior) {
 506             onStateChanged();
 507         }
 508
 509         String lastLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastLeaderId();
 510         String lastValidLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastValidLeaderId();
 511         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 512
 513         // it can happen that the state has not changed but the leader has changed.
 514         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 515         if (!Objects.equals(lastLeaderId, currentBehavior.getLeaderId())
 516                 || oldBehaviorState.getLeaderPayloadVersion() != currentBehavior.getLeaderPayloadVersion()) {
 517             if (roleChangeNotifier.isPresent()) {
 518                 roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), currentBehavior.getLeaderId(),
 519                         currentBehavior.getLeaderPayloadVersion()), getSelf());
 520             }
 521
 522             onLeaderChanged(lastValidLeaderId, currentBehavior.getLeaderId());
 523
 524             RaftActorLeadershipTransferCohort leadershipTransferInProgress =
 525                     context.getRaftActorLeadershipTransferCohort();
 526             if (leadershipTransferInProgress != null) {
 527                 leadershipTransferInProgress.onNewLeader(currentBehavior.getLeaderId());
 528             }
 529
 530             serverConfigurationSupport.onNewLeader(currentBehavior.getLeaderId());
 531         }
 532
 533         if (roleChangeNotifier.isPresent()
 534                 && (oldBehavior == null || oldBehavior.state() != currentBehavior.state())) {
 535             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 536                     currentBehavior.state().name()), getSelf());
 537         }
 538     }
 539
 540     private void handleApplyState(final ApplyState applyState) {
 541         long startTime = System.nanoTime();
 542
 543         Payload payload = applyState.getReplicatedLogEntry().getData();
 544         if (LOG.isDebugEnabled()) {
 545             LOG.debug("{}: Applying state for log index {} data {}",
 546                 persistenceId(), applyState.getReplicatedLogEntry().getIndex(), payload);
 547         }
 548
 549         if (!(payload instanceof NoopPayload) && !(payload instanceof ServerConfigurationPayload)) {
 550             applyState(applyState.getClientActor(), applyState.getIdentifier(), payload);
 551         }
 552
 553         long elapsedTime = System.nanoTime() - startTime;
 554         if (elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS) {
 555             LOG.debug("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 556                     TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 557         }
 558
 559         // Send the ApplyState message back to self to handle further processing asynchronously.
 560         self().tell(applyState, self());
 561     }
 562
 563     protected LeaderStateChanged newLeaderStateChanged(final String memberId, final String leaderId,
 564             final short leaderPayloadVersion) {
 565         return new LeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
 566     }
 567
 568     @Override
 569     public long snapshotSequenceNr() {
 570         // When we do a snapshot capture, we also capture and save the sequence-number of the persistent journal,
 571         // so that we can delete the persistent journal based on the saved sequence-number
 572         // However , when akka replays the journal during recovery, it replays it from the sequence number when the
 573         // snapshot was saved and not the number we saved. We would want to override it , by asking akka to use the
 574         // last-sequence number known to us.
 575         return context.getSnapshotManager().getLastSequenceNumber();
 576     }
 577
 578     /**
 579      * Persists the given Payload in the journal and replicates to any followers. After successful completion,
 580      * {@link #applyState(ActorRef, Identifier, Object)} is notified.
 581      *
 582      * @param clientActor optional ActorRef that is provided via the applyState callback
 583      * @param identifier the payload identifier
 584      * @param data the payload data to persist
 585      * @param batchHint if true, an attempt is made to delay immediate replication and batch the payload with
 586      *        subsequent payloads for efficiency. Otherwise the payload is immediately replicated.
 587      */
 588     protected final void persistData(final ActorRef clientActor, final Identifier identifier, final Payload data,
 589             final boolean batchHint) {
 590         ReplicatedLogEntry replicatedLogEntry = new SimpleReplicatedLogEntry(
 591             context.getReplicatedLog().lastIndex() + 1,
 592             context.getTermInformation().getCurrentTerm(), data);
 593         replicatedLogEntry.setPersistencePending(true);
 594
 595         LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 596
 597         final RaftActorContext raftContext = getRaftActorContext();
 598
 599         boolean wasAppended = replicatedLog().appendAndPersist(replicatedLogEntry, persistedLogEntry -> {
 600             // Clear the persistence pending flag in the log entry.
 601             persistedLogEntry.setPersistencePending(false);
 602
 603             if (!hasFollowers()) {
 604                 // Increment the Commit Index and the Last Applied values
 605                 raftContext.setCommitIndex(persistedLogEntry.getIndex());
 606                 raftContext.setLastApplied(persistedLogEntry.getIndex());
 607
 608                 // Apply the state immediately.
 609                 handleApplyState(new ApplyState(clientActor, identifier, persistedLogEntry));
 610
 611                 // Send a ApplyJournalEntries message so that we write the fact that we applied
 612                 // the state to durable storage
 613                 self().tell(new ApplyJournalEntries(persistedLogEntry.getIndex()), self());
 614
 615             } else {
 616                 context.getReplicatedLog().captureSnapshotIfReady(replicatedLogEntry);
 617
 618                 // Local persistence is complete so send the CheckConsensusReached message to the behavior (which
 619                 // normally should still be the leader) to check if consensus has now been reached in conjunction with
 620                 // follower replication.
 621                 getCurrentBehavior().handleMessage(getSelf(), CheckConsensusReached.INSTANCE);
 622             }
 623         }, true);
 624
 625         if (wasAppended && hasFollowers()) {
 626             // Send log entry for replication.
 627             getCurrentBehavior().handleMessage(getSelf(), new Replicate(clientActor, identifier, replicatedLogEntry,
 628                     !batchHint));
 629         }
 630     }
 631
 632     private ReplicatedLog replicatedLog() {
 633         return context.getReplicatedLog();
 634     }
 635
 636     protected String getId() {
 637         return context.getId();
 638     }
 639
 640     @VisibleForTesting
 641     void setCurrentBehavior(final RaftActorBehavior behavior) {
 642         context.setCurrentBehavior(behavior);
 643     }
 644
 645     protected RaftActorBehavior getCurrentBehavior() {
 646         return context.getCurrentBehavior();
 647     }
 648
 649     /**
 650      * Derived actors can call the isLeader method to check if the current
 651      * RaftActor is the Leader or not.
 652      *
 653      * @return true it this RaftActor is a Leader false otherwise
 654      */
 655     protected boolean isLeader() {
 656         return context.getId().equals(getCurrentBehavior().getLeaderId());
 657     }
 658
 659     protected final boolean isLeaderActive() {
 660         return getRaftState() != RaftState.IsolatedLeader && getRaftState() != RaftState.PreLeader
 661                 && !shuttingDown && !isLeadershipTransferInProgress();
 662     }
 663
 664     protected boolean isLeadershipTransferInProgress() {
 665         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
 666         return leadershipTransferInProgress != null && leadershipTransferInProgress.isTransferring();
 667     }
 668
 669     /**
 670      * Derived actor can call getLeader if they need a reference to the Leader.
 671      * This would be useful for example in forwarding a request to an actor
 672      * which is the leader
 673      *
 674      * @return A reference to the leader if known, null otherwise
 675      */
 676     public ActorSelection getLeader() {
 677         String leaderAddress = getLeaderAddress();
 678
 679         if (leaderAddress == null) {
 680             return null;
 681         }
 682
 683         return context.actorSelection(leaderAddress);
 684     }
 685
 686     /**
 687      * Returns the id of the current leader.
 688      *
 689      * @return the current leader's id
 690      */
 691     protected final String getLeaderId() {
 692         return getCurrentBehavior().getLeaderId();
 693     }
 694
 695     @VisibleForTesting
 696     protected final RaftState getRaftState() {
 697         return getCurrentBehavior().state();
 698     }
 699
 700     protected Long getCurrentTerm() {
 701         return context.getTermInformation().getCurrentTerm();
 702     }
 703
 704     protected RaftActorContext getRaftActorContext() {
 705         return context;
 706     }
 707
 708     protected void updateConfigParams(final ConfigParams configParams) {
 709
 710         // obtain the RaftPolicy for oldConfigParams and the updated one.
 711         String oldRaftPolicy = context.getConfigParams().getCustomRaftPolicyImplementationClass();
 712         String newRaftPolicy = configParams.getCustomRaftPolicyImplementationClass();
 713
 714         LOG.debug("{}: RaftPolicy used with prev.config {}, RaftPolicy used with newConfig {}", persistenceId(),
 715             oldRaftPolicy, newRaftPolicy);
 716         context.setConfigParams(configParams);
 717         if (!Objects.equals(oldRaftPolicy, newRaftPolicy)) {
 718             // The RaftPolicy was modified. If the current behavior is Follower then re-initialize to Follower
 719             // but transfer the previous leaderId so it doesn't immediately try to schedule an election. This
 720             // avoids potential disruption. Otherwise, switch to Follower normally.
 721             RaftActorBehavior behavior = getCurrentBehavior();
 722             if (behavior != null && behavior.state() == RaftState.Follower) {
 723                 String previousLeaderId = behavior.getLeaderId();
 724                 short previousLeaderPayloadVersion = behavior.getLeaderPayloadVersion();
 725
 726                 LOG.debug("{}: Re-initializing to Follower with previous leaderId {}", persistenceId(),
 727                         previousLeaderId);
 728
 729                 changeCurrentBehavior(new Follower(context, previousLeaderId, previousLeaderPayloadVersion));
 730             } else {
 731                 initializeBehavior();
 732             }
 733         }
 734     }
 735
 736     public final DataPersistenceProvider persistence() {
 737         return delegatingPersistenceProvider.getDelegate();
 738     }
 739
 740     public void setPersistence(final DataPersistenceProvider provider) {
 741         delegatingPersistenceProvider.setDelegate(provider);
 742     }
 743
 744     protected void setPersistence(final boolean persistent) {
 745         DataPersistenceProvider currentPersistence = persistence();
 746         if (persistent && (currentPersistence == null || !currentPersistence.isRecoveryApplicable())) {
 747             setPersistence(new PersistentDataProvider(this));
 748
 749             if (getCurrentBehavior() != null) {
 750                 LOG.info("{}: Persistence has been enabled - capturing snapshot", persistenceId());
 751                 captureSnapshot();
 752             }
 753         } else if (!persistent && (currentPersistence == null || currentPersistence.isRecoveryApplicable())) {
 754             setPersistence(new NonPersistentDataProvider(this) {
 755                 /*
 756                  * The way snapshotting works is,
 757                  * <ol>
 758                  * <li> RaftActor calls createSnapshot on the Shard
 759                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 760                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 761                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 762                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 763                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 764                  * </ol>
 765                  */
 766                 @Override
 767                 public void saveSnapshot(final Object object) {
 768                     // Make saving Snapshot successful
 769                     // Committing the snapshot here would end up calling commit in the creating state which would
 770                     // be a state violation. That's why now we send a message to commit the snapshot.
 771                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
 772                 }
 773             });
 774         }
 775     }
 776
 777     /**
 778      * setPeerAddress sets the address of a known peer at a later time.
 779      *
 780      * <p>
 781      * This is to account for situations where a we know that a peer
 782      * exists but we do not know an address up-front. This may also be used in
 783      * situations where a known peer starts off in a different location and we
 784      * need to change it's address
 785      *
 786      * <p>
 787      * Note that if the peerId does not match the list of peers passed to
 788      * this actor during construction an IllegalStateException will be thrown.
 789      */
 790     protected void setPeerAddress(final String peerId, final String peerAddress) {
 791         context.setPeerAddress(peerId, peerAddress);
 792     }
 793
 794     /**
 795      * The applyState method will be called by the RaftActor when some data
 796      * needs to be applied to the actor's state.
 797      *
 798      * @param clientActor A reference to the client who sent this message. This
 799      *                    is the same reference that was passed to persistData
 800      *                    by the derived actor. clientActor may be null when
 801      *                    the RaftActor is behaving as a follower or during
 802      *                    recovery.
 803      * @param identifier  The identifier of the persisted data. This is also
 804      *                    the same identifier that was passed to persistData by
 805      *                    the derived actor. identifier may be null when
 806      *                    the RaftActor is behaving as a follower or during
 807      *                    recovery
 808      * @param data        A piece of data that was persisted by the persistData call.
 809      *                    This should NEVER be null.
 810      */
 811     protected abstract void applyState(ActorRef clientActor, Identifier identifier, Object data);
 812
 813     /**
 814      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
 815      */
 816     @Nonnull
 817     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
 818
 819     /**
 820      * This method is called when recovery is complete.
 821      */
 822     protected abstract void onRecoveryComplete();
 823
 824     /**
 825      * Returns the RaftActorSnapshotCohort to participate in snapshot captures.
 826      */
 827     @Nonnull
 828     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
 829
 830     /**
 831      * This method will be called by the RaftActor when the state of the
 832      * RaftActor changes. The derived actor can then use methods like
 833      * isLeader or getLeader to do something useful
 834      */
 835     protected abstract void onStateChanged();
 836
 837     /**
 838      * Notifier Actor for this RaftActor to notify when a role change happens.
 839      *
 840      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 841      */
 842     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 843
 844     /**
 845      * This method is called on the leader when a voting change operation completes.
 846      */
 847     protected void onVotingStateChangeComplete() {
 848     }
 849
 850     /**
 851      * This method is called prior to operations such as leadership transfer and actor shutdown when the leader
 852      * must pause or stop its duties. This method allows derived classes to gracefully pause or finish current
 853      * work prior to performing the operation. On completion of any work, the run method must be called on the
 854      * given Runnable to proceed with the given operation. <b>Important:</b> the run method must be called on
 855      * this actor's thread dispatcher as as it modifies internal state.
 856      *
 857      * <p>
 858      * The default implementation immediately runs the operation.
 859      *
 860      * @param operation the operation to run
 861      */
 862     protected void pauseLeader(final Runnable operation) {
 863         operation.run();
 864     }
 865
 866     /**
 867      * This method is invoked when the actions hooked to the leader becoming paused failed to execute and the leader
 868      * should resume normal operations.
 869      *
 870      * <p>
 871      * Note this method can be invoked even before the operation supplied to {@link #pauseLeader(Runnable)} is invoked.
 872      */
 873     protected void unpauseLeader() {
 874
 875     }
 876
 877     protected void onLeaderChanged(final String oldLeader, final String newLeader) {
 878     }
 879
 880     private String getLeaderAddress() {
 881         if (isLeader()) {
 882             return getSelf().path().toString();
 883         }
 884         String leaderId = getLeaderId();
 885         if (leaderId == null) {
 886             return null;
 887         }
 888         String peerAddress = context.getPeerAddress(leaderId);
 889         LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}", persistenceId(), leaderId, peerAddress);
 890
 891         return peerAddress;
 892     }
 893
 894     protected boolean hasFollowers() {
 895         return getRaftActorContext().hasFollowers();
 896     }
 897
 898     private void captureSnapshot() {
 899         SnapshotManager snapshotManager = context.getSnapshotManager();
 900
 901         if (!snapshotManager.isCapturing()) {
 902             final long idx = getCurrentBehavior().getReplicatedToAllIndex();
 903             LOG.debug("Take a snapshot of current state. lastReplicatedLog is {} and replicatedToAllIndex is {}",
 904                 replicatedLog().last(), idx);
 905
 906             snapshotManager.capture(replicatedLog().last(), idx);
 907         }
 908     }
 909
 910     /**
 911      * Switch this member to non-voting status. This is a no-op for all behaviors except when we are the leader,
 912      * in which case we need to step down.
 913      */
 914     void becomeNonVoting() {
 915         if (isLeader()) {
 916             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 917                 @Override
 918                 public void onSuccess(final ActorRef raftActorRef) {
 919                     LOG.debug("{}: leader transfer succeeded after change to non-voting", persistenceId());
 920                     ensureFollowerState();
 921                 }
 922
 923                 @Override
 924                 public void onFailure(final ActorRef raftActorRef) {
 925                     LOG.debug("{}: leader transfer failed after change to non-voting", persistenceId());
 926                     ensureFollowerState();
 927                 }
 928
 929                 private void ensureFollowerState() {
 930                     // Whether or not leadership transfer succeeded, we have to step down as leader and
 931                     // switch to Follower so ensure that.
 932                     if (getRaftState() != RaftState.Follower) {
 933                         initializeBehavior();
 934                     }
 935                 }
 936             }, null, RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
 937         }
 938     }
 939
 940     /**
 941      * A point-in-time capture of {@link RaftActorBehavior} state critical for transitioning between behaviors.
 942      */
 943     private abstract static class BehaviorState implements Immutable {
 944         @Nullable abstract RaftActorBehavior getBehavior();
 945
 946         @Nullable abstract String getLastValidLeaderId();
 947
 948         @Nullable abstract String getLastLeaderId();
 949
 950         @Nullable abstract short getLeaderPayloadVersion();
 951     }
 952
 953     /**
 954      * A {@link BehaviorState} corresponding to non-null {@link RaftActorBehavior} state.
 955      */
 956     private static final class SimpleBehaviorState extends BehaviorState {
 957         private final RaftActorBehavior behavior;
 958         private final String lastValidLeaderId;
 959         private final String lastLeaderId;
 960         private final short leaderPayloadVersion;
 961
 962         SimpleBehaviorState(final String lastValidLeaderId, final String lastLeaderId,
 963                 final RaftActorBehavior behavior) {
 964             this.lastValidLeaderId = lastValidLeaderId;
 965             this.lastLeaderId = lastLeaderId;
 966             this.behavior = Preconditions.checkNotNull(behavior);
 967             this.leaderPayloadVersion = behavior.getLeaderPayloadVersion();
 968         }
 969
 970         @Override
 971         RaftActorBehavior getBehavior() {
 972             return behavior;
 973         }
 974
 975         @Override
 976         String getLastValidLeaderId() {
 977             return lastValidLeaderId;
 978         }
 979
 980         @Override
 981         short getLeaderPayloadVersion() {
 982             return leaderPayloadVersion;
 983         }
 984
 985         @Override
 986         String getLastLeaderId() {
 987             return lastLeaderId;
 988         }
 989     }
 990
 991     /**
 992      * Class tracking behavior-related information, which we need to keep around and pass across behavior switches.
 993      * An instance is created for each RaftActor. It has two functions:
 994      * - it keeps track of the last leader ID we have encountered since we have been created
 995      * - it creates state capture needed to transition from one behavior to the next
 996      */
 997     private static final class BehaviorStateTracker {
 998         /**
 999          * A {@link BehaviorState} corresponding to null {@link RaftActorBehavior} state. Since null behavior is only
1000          * allowed before we receive the first message, we know the leader ID to be null.
1001          */
1002         private static final BehaviorState NULL_BEHAVIOR_STATE = new BehaviorState() {
1003             @Override
1004             RaftActorBehavior getBehavior() {
1005                 return null;
1006             }
1007
1008             @Override
1009             String getLastValidLeaderId() {
1010                 return null;
1011             }
1012
1013             @Override
1014             short getLeaderPayloadVersion() {
1015                 return -1;
1016             }
1017
1018             @Override
1019             String getLastLeaderId() {
1020                 return null;
1021             }
1022         };
1023
1024         private String lastValidLeaderId;
1025         private String lastLeaderId;
1026
1027         BehaviorState capture(final RaftActorBehavior behavior) {
1028             if (behavior == null) {
1029                 Verify.verify(lastValidLeaderId == null, "Null behavior with non-null last leader");
1030                 return NULL_BEHAVIOR_STATE;
1031             }
1032
1033             lastLeaderId = behavior.getLeaderId();
1034             if (lastLeaderId != null) {
1035                 lastValidLeaderId = lastLeaderId;
1036             }
1037
1038             return new SimpleBehaviorState(lastValidLeaderId, lastLeaderId, behavior);
1039         }
1040     }
1041 }