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 package org.opendaylight.controller.cluster.raft;
  10
  11 import static com.google.common.base.Verify.verify;
  12 import static java.util.Objects.requireNonNull;
  13
  14 import akka.actor.ActorRef;
  15 import akka.actor.ActorSelection;
  16 import akka.actor.PoisonPill;
  17 import akka.actor.Status;
  18 import akka.persistence.JournalProtocol;
  19 import akka.persistence.SnapshotProtocol;
  20 import com.google.common.annotations.VisibleForTesting;
  21 import com.google.common.collect.ImmutableList;
  22 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  23 import java.util.HashMap;
  24 import java.util.Map;
  25 import java.util.Objects;
  26 import java.util.Optional;
  27 import java.util.concurrent.TimeUnit;
  28 import org.apache.commons.lang3.time.DurationFormatUtils;
  29 import org.eclipse.jdt.annotation.NonNull;
  30 import org.eclipse.jdt.annotation.Nullable;
  31 import org.opendaylight.controller.cluster.DataPersistenceProvider;
  32 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
  33 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
  34 import org.opendaylight.controller.cluster.PersistentDataProvider;
  35 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
  36 import org.opendaylight.controller.cluster.mgmt.api.FollowerInfo;
  37 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
  38 import org.opendaylight.controller.cluster.notifications.RoleChanged;
  39 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  40 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
  41 import org.opendaylight.controller.cluster.raft.base.messages.InitiateCaptureSnapshot;
  42 import org.opendaylight.controller.cluster.raft.base.messages.LeaderTransitioning;
  43 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  44 import org.opendaylight.controller.cluster.raft.base.messages.SwitchBehavior;
  45 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
  46 import org.opendaylight.controller.cluster.raft.behaviors.AbstractRaftActorBehavior;
  47 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  48 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  49 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  50 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  51 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
  52 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
  53 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
  54 import org.opendaylight.controller.cluster.raft.messages.Payload;
  55 import org.opendaylight.controller.cluster.raft.messages.RequestLeadership;
  56 import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
  57 import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
  58 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  59 import org.opendaylight.controller.cluster.raft.persisted.SimpleReplicatedLogEntry;
  60 import org.opendaylight.yangtools.concepts.Identifier;
  61 import org.opendaylight.yangtools.concepts.Immutable;
  62
  63 /**
  64  * RaftActor encapsulates a state machine that needs to be kept synchronized
  65  * in a cluster. It implements the RAFT algorithm as described in the paper
  66  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  67  * In Search of an Understandable Consensus Algorithm</a>
  68  *
  69  * <p>
  70  * RaftActor has 3 states and each state has a certain behavior associated
  71  * with it. A Raft actor can behave as,
  72  * <ul>
  73  * <li> A Leader </li>
  74  * <li> A Follower (or) </li>
  75  * <li> A Candidate </li>
  76  * </ul>
  77  *
  78  * <p>
  79  * A RaftActor MUST be a Leader in order to accept requests from clients to
  80  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  81  * a Leader it is also responsible for ensuring that all followers ultimately
  82  * have the same log and therefore the same state machine as itself.
  83  *
  84  * <p>
  85  * The current behavior of a RaftActor determines how election for leadership
  86  * is initiated and how peer RaftActors react to request for votes.
  87  *
  88  * <p>
  89  * Each RaftActor also needs to know the current election term. It uses this
  90  * information for a couple of things. One is to simply figure out who it
  91  * voted for in the last election. Another is to figure out if the message
  92  * it received to update it's state is stale.
  93  *
  94  * <p>
  95  * The RaftActor uses akka-persistence to store it's replicated log.
  96  * Furthermore through it's behaviors a Raft Actor determines
  97  * <ul>
  98  * <li> when a log entry should be persisted </li>
  99  * <li> when a log entry should be applied to the state machine (and) </li>
 100  * <li> when a snapshot should be saved </li>
 101  * </ul>
 102  */
 103 public abstract class RaftActor extends AbstractUntypedPersistentActor {
 104     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50);
 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     @SuppressFBWarnings(value = "MC_OVERRIDABLE_METHOD_CALL_IN_CONSTRUCTOR", justification = "Akka class design")
 127     protected RaftActor(final String id, final Map<String, String> peerAddresses,
 128          final Optional<ConfigParams> configParams, final short payloadVersion) {
 129
 130         persistentProvider = new PersistentDataProvider(this);
 131         delegatingPersistenceProvider = new RaftActorDelegatingPersistentDataProvider(null, persistentProvider);
 132
 133         context = new RaftActorContextImpl(getSelf(), getContext(), id,
 134             new ElectionTermImpl(persistentProvider, id, LOG), -1, -1, peerAddresses,
 135             configParams.isPresent() ? configParams.orElseThrow() : new DefaultConfigParamsImpl(),
 136             delegatingPersistenceProvider, this::handleApplyState, LOG, this::executeInSelf);
 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() throws Exception {
 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 applyState) {
 229             if (!hasFollowers()) {
 230                 // for single node, the capture should happen after the apply state
 231                 // as we delete messages from the persistent journal which have made it to the snapshot
 232                 // capturing the snapshot before applying makes the persistent journal and snapshot out of sync
 233                 // and recovery shows data missing
 234                 context.getReplicatedLog().captureSnapshotIfReady(applyState.getReplicatedLogEntry());
 235
 236                 context.getSnapshotManager().trimLog(context.getLastApplied());
 237             }
 238
 239             possiblyHandleBehaviorMessage(message);
 240         } else if (message instanceof ApplyJournalEntries applyEntries) {
 241             LOG.debug("{}: Persisting ApplyJournalEntries with index={}", persistenceId(), applyEntries.getToIndex());
 242
 243             persistence().persistAsync(applyEntries, NoopProcedure.instance());
 244         } else if (message instanceof FindLeader) {
 245             getSender().tell(new FindLeaderReply(getLeaderAddress()), getSelf());
 246         } else if (message instanceof GetOnDemandRaftState) {
 247             onGetOnDemandRaftStats();
 248         } else if (message instanceof InitiateCaptureSnapshot) {
 249             captureSnapshot();
 250         } else if (message instanceof SwitchBehavior switchBehavior) {
 251             switchBehavior(switchBehavior);
 252         } else if (message instanceof LeaderTransitioning leaderTransitioning) {
 253             onLeaderTransitioning(leaderTransitioning);
 254         } else if (message instanceof Shutdown) {
 255             onShutDown();
 256         } else if (message instanceof Runnable runnable) {
 257             runnable.run();
 258         } else if (message instanceof NoopPayload noopPayload) {
 259             persistData(null, null, noopPayload, false);
 260         } else if (message instanceof RequestLeadership requestLeadership) {
 261             onRequestLeadership(requestLeadership);
 262         } else if (!possiblyHandleBehaviorMessage(message)) {
 263             if (message instanceof JournalProtocol.Response response
 264                 && delegatingPersistenceProvider.handleJournalResponse(response)) {
 265                 LOG.debug("{}: handled a journal response", persistenceId());
 266             } else if (message instanceof SnapshotProtocol.Response response
 267                 && delegatingPersistenceProvider.handleSnapshotResponse(response)) {
 268                 LOG.debug("{}: handled a snapshot response", persistenceId());
 269             } else {
 270                 handleNonRaftCommand(message);
 271             }
 272         }
 273     }
 274
 275     private void onRequestLeadership(final RequestLeadership message) {
 276         LOG.debug("{}: onRequestLeadership {}", persistenceId(), message);
 277         if (!isLeader()) {
 278             // non-leader cannot satisfy leadership request
 279             LOG.warn("{}: onRequestLeadership {} was sent to non-leader."
 280                     + " Current behavior: {}. Sending failure response",
 281                     persistenceId(), message, getCurrentBehavior().state());
 282             message.getReplyTo().tell(new LeadershipTransferFailedException("Cannot transfer leader to "
 283                     + message.getRequestedFollowerId()
 284                     + ". RequestLeadership message was sent to non-leader " + persistenceId()), getSelf());
 285             return;
 286         }
 287
 288         final String requestedFollowerId = message.getRequestedFollowerId();
 289         final ActorRef replyTo = message.getReplyTo();
 290         initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 291             @Override
 292             public void onSuccess(final ActorRef raftActorRef) {
 293                 // sanity check
 294                 if (!requestedFollowerId.equals(getLeaderId())) {
 295                     onFailure(raftActorRef);
 296                 }
 297
 298                 LOG.debug("{}: Leadership transferred successfully to {}", persistenceId(), requestedFollowerId);
 299                 replyTo.tell(new Status.Success(null), getSelf());
 300             }
 301
 302             @Override
 303             public void onFailure(final ActorRef raftActorRef) {
 304                 LOG.debug("{}: LeadershipTransfer request from {} failed", persistenceId(), requestedFollowerId);
 305                 replyTo.tell(new Status.Failure(
 306                         new LeadershipTransferFailedException(
 307                                 "Failed to transfer leadership to " + requestedFollowerId
 308                                         + ". Follower is not ready to become leader")),
 309                         getSelf());
 310             }
 311         }, message.getRequestedFollowerId(), RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
 312     }
 313
 314     private boolean possiblyHandleBehaviorMessage(final Object message) {
 315         final RaftActorBehavior currentBehavior = getCurrentBehavior();
 316         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
 317
 318         // A behavior indicates that it processed the change by returning a reference to the next behavior
 319         // to be used. A null return indicates it has not processed the message and we should be passing it to
 320         // the subclass for handling.
 321         final RaftActorBehavior nextBehavior = currentBehavior.handleMessage(getSender(), message);
 322         if (nextBehavior != null) {
 323             switchBehavior(state, nextBehavior);
 324             return true;
 325         }
 326
 327         return false;
 328     }
 329
 330     private void initiateLeadershipTransfer(final RaftActorLeadershipTransferCohort.OnComplete onComplete,
 331             final @Nullable String followerId, final long newLeaderTimeoutInMillis) {
 332         LOG.debug("{}: Initiating leader transfer", persistenceId());
 333
 334         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
 335         if (leadershipTransferInProgress == null) {
 336             leadershipTransferInProgress = new RaftActorLeadershipTransferCohort(this, followerId);
 337             leadershipTransferInProgress.setNewLeaderTimeoutInMillis(newLeaderTimeoutInMillis);
 338             leadershipTransferInProgress.addOnComplete(new RaftActorLeadershipTransferCohort.OnComplete() {
 339                 @Override
 340                 public void onSuccess(final ActorRef raftActorRef) {
 341                     context.setRaftActorLeadershipTransferCohort(null);
 342                 }
 343
 344                 @Override
 345                 public void onFailure(final ActorRef raftActorRef) {
 346                     context.setRaftActorLeadershipTransferCohort(null);
 347                 }
 348             });
 349
 350             leadershipTransferInProgress.addOnComplete(onComplete);
 351
 352             context.setRaftActorLeadershipTransferCohort(leadershipTransferInProgress);
 353             leadershipTransferInProgress.init();
 354
 355         } else {
 356             LOG.debug("{}: prior leader transfer in progress - adding callback", persistenceId());
 357             leadershipTransferInProgress.addOnComplete(onComplete);
 358         }
 359     }
 360
 361     private void onShutDown() {
 362         LOG.debug("{}: onShutDown", persistenceId());
 363
 364         if (shuttingDown) {
 365             return;
 366         }
 367
 368         shuttingDown = true;
 369
 370         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 371         switch (currentBehavior.state()) {
 372             case Leader:
 373             case PreLeader:
 374                 // Fall-through to more work
 375                 break;
 376             default:
 377                 // For non-leaders shutdown is a no-op
 378                 self().tell(PoisonPill.getInstance(), self());
 379                 return;
 380         }
 381
 382         if (context.hasFollowers()) {
 383             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 384                 @Override
 385                 public void onSuccess(final ActorRef raftActorRef) {
 386                     LOG.debug("{}: leader transfer succeeded - sending PoisonPill", persistenceId());
 387                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 388                 }
 389
 390                 @Override
 391                 public void onFailure(final ActorRef raftActorRef) {
 392                     LOG.debug("{}: leader transfer failed - sending PoisonPill", persistenceId());
 393                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
 394                 }
 395             }, null, TimeUnit.MILLISECONDS.convert(2, TimeUnit.SECONDS));
 396         } else {
 397             pauseLeader(new TimedRunnable(context.getConfigParams().getElectionTimeOutInterval(), this) {
 398                 @Override
 399                 protected void doRun() {
 400                     self().tell(PoisonPill.getInstance(), self());
 401                 }
 402
 403                 @Override
 404                 protected void doCancel() {
 405                     self().tell(PoisonPill.getInstance(), self());
 406                 }
 407             });
 408         }
 409     }
 410
 411     private void onLeaderTransitioning(final LeaderTransitioning leaderTransitioning) {
 412         LOG.debug("{}: onLeaderTransitioning: {}", persistenceId(), leaderTransitioning);
 413         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 414         if (getRaftState() == RaftState.Follower && roleChangeNotifier.isPresent()
 415                 && leaderTransitioning.getLeaderId().equals(getCurrentBehavior().getLeaderId())) {
 416             roleChangeNotifier.orElseThrow().tell(newLeaderStateChanged(getId(), null,
 417                 getCurrentBehavior().getLeaderPayloadVersion()), getSelf());
 418         }
 419     }
 420
 421     private void switchBehavior(final SwitchBehavior message) {
 422         if (!getRaftActorContext().getRaftPolicy().automaticElectionsEnabled()) {
 423             RaftState newState = message.getNewState();
 424             if (newState == RaftState.Leader || newState == RaftState.Follower) {
 425                 getRaftActorContext().getTermInformation().updateAndPersist(message.getNewTerm(), "");
 426                 switchBehavior(behaviorStateTracker.capture(getCurrentBehavior()),
 427                     AbstractRaftActorBehavior.createBehavior(context, message.getNewState()));
 428             } else {
 429                 LOG.warn("Switching to behavior : {} - not supported", newState);
 430             }
 431         }
 432     }
 433
 434     private void switchBehavior(final BehaviorState oldBehaviorState, final RaftActorBehavior nextBehavior) {
 435         setCurrentBehavior(nextBehavior);
 436         handleBehaviorChange(oldBehaviorState, nextBehavior);
 437     }
 438
 439     @VisibleForTesting
 440     RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
 441         return new RaftActorSnapshotMessageSupport(context, getRaftActorSnapshotCohort());
 442     }
 443
 444     private void onGetOnDemandRaftStats() {
 445         // Debugging message to retrieve raft stats.
 446
 447         Map<String, String> peerAddresses = new HashMap<>();
 448         Map<String, Boolean> peerVotingStates = new HashMap<>();
 449         for (PeerInfo info: context.getPeers()) {
 450             peerVotingStates.put(info.getId(), info.isVoting());
 451             peerAddresses.put(info.getId(), info.getAddress() != null ? info.getAddress() : "");
 452         }
 453
 454         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 455         final var builder = newOnDemandRaftStateBuilder()
 456                 .commitIndex(context.getCommitIndex())
 457                 .currentTerm(context.getTermInformation().getCurrentTerm())
 458                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 459                 .inMemoryJournalLogSize(replicatedLog().size())
 460                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 461                 .lastApplied(context.getLastApplied())
 462                 .lastIndex(replicatedLog().lastIndex())
 463                 .lastTerm(replicatedLog().lastTerm())
 464                 .leader(getLeaderId())
 465                 .raftState(currentBehavior.state().toString())
 466                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 467                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 468                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 469                 .votedFor(context.getTermInformation().getVotedFor())
 470                 .isVoting(context.isVotingMember())
 471                 .peerAddresses(peerAddresses)
 472                 .peerVotingStates(peerVotingStates)
 473                 .customRaftPolicyClassName(context.getConfigParams().getCustomRaftPolicyImplementationClass());
 474
 475         ReplicatedLogEntry lastLogEntry = replicatedLog().last();
 476         if (lastLogEntry != null) {
 477             builder.lastLogIndex(lastLogEntry.getIndex());
 478             builder.lastLogTerm(lastLogEntry.getTerm());
 479         }
 480
 481         if (getCurrentBehavior() instanceof AbstractLeader leader) {
 482             builder.followerInfoList(leader.getFollowerIds().stream()
 483                 .map(leader::getFollower)
 484                 .map(info -> new FollowerInfo(info.getId(), info.getNextIndex(), info.getMatchIndex(),
 485                     info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(
 486                         TimeUnit.NANOSECONDS.toMillis(info.nanosSinceLastActivity())),
 487                     context.getPeerInfo(info.getId()).isVoting()))
 488                 .collect(ImmutableList.toImmutableList()));
 489         }
 490
 491         sender().tell(builder.build(), self());
 492
 493     }
 494
 495     protected OnDemandRaftState.AbstractBuilder<?, ?> newOnDemandRaftStateBuilder() {
 496         return OnDemandRaftState.builder();
 497     }
 498
 499     private void handleBehaviorChange(final BehaviorState oldBehaviorState, final RaftActorBehavior currentBehavior) {
 500         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 501
 502         if (oldBehavior != currentBehavior) {
 503             onStateChanged();
 504         }
 505
 506         String lastLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastLeaderId();
 507         String lastValidLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastValidLeaderId();
 508         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 509
 510         // it can happen that the state has not changed but the leader has changed.
 511         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 512         if (!Objects.equals(lastLeaderId, currentBehavior.getLeaderId())
 513                 || oldBehaviorState.getLeaderPayloadVersion() != currentBehavior.getLeaderPayloadVersion()) {
 514             if (roleChangeNotifier.isPresent()) {
 515                 roleChangeNotifier.orElseThrow().tell(newLeaderStateChanged(getId(), currentBehavior.getLeaderId(),
 516                         currentBehavior.getLeaderPayloadVersion()), getSelf());
 517             }
 518
 519             onLeaderChanged(lastValidLeaderId, currentBehavior.getLeaderId());
 520
 521             RaftActorLeadershipTransferCohort leadershipTransferInProgress =
 522                     context.getRaftActorLeadershipTransferCohort();
 523             if (leadershipTransferInProgress != null) {
 524                 leadershipTransferInProgress.onNewLeader(currentBehavior.getLeaderId());
 525             }
 526
 527             serverConfigurationSupport.onNewLeader(currentBehavior.getLeaderId());
 528         }
 529
 530         if (roleChangeNotifier.isPresent()
 531                 && (oldBehavior == null || oldBehavior.state() != currentBehavior.state())) {
 532             roleChangeNotifier.orElseThrow().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 533                     currentBehavior.state().name()), getSelf());
 534         }
 535     }
 536
 537     private void handleApplyState(final ApplyState applyState) {
 538         long startTime = System.nanoTime();
 539
 540         Payload payload = applyState.getReplicatedLogEntry().getData();
 541         if (LOG.isDebugEnabled()) {
 542             LOG.debug("{}: Applying state for log index {} data {}",
 543                 persistenceId(), applyState.getReplicatedLogEntry().getIndex(), payload);
 544         }
 545
 546         if (!(payload instanceof NoopPayload) && !(payload instanceof ServerConfigurationPayload)) {
 547             applyState(applyState.getClientActor(), applyState.getIdentifier(), payload);
 548         }
 549
 550         long elapsedTime = System.nanoTime() - startTime;
 551         if (elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS) {
 552             LOG.debug("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 553                     TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 554         }
 555
 556         // Send the ApplyState message back to self to handle further processing asynchronously.
 557         self().tell(applyState, self());
 558     }
 559
 560     protected LeaderStateChanged newLeaderStateChanged(final String memberId, final String leaderId,
 561             final short leaderPayloadVersion) {
 562         return new LeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
 563     }
 564
 565     @Override
 566     public long snapshotSequenceNr() {
 567         // When we do a snapshot capture, we also capture and save the sequence-number of the persistent journal,
 568         // so that we can delete the persistent journal based on the saved sequence-number
 569         // However , when akka replays the journal during recovery, it replays it from the sequence number when the
 570         // snapshot was saved and not the number we saved. We would want to override it , by asking akka to use the
 571         // last-sequence number known to us.
 572         return context.getSnapshotManager().getLastSequenceNumber();
 573     }
 574
 575     /**
 576      * Persists the given Payload in the journal and replicates to any followers. After successful completion,
 577      * {@link #applyState(ActorRef, Identifier, Object)} is notified.
 578      *
 579      * @param clientActor optional ActorRef that is provided via the applyState callback
 580      * @param identifier the payload identifier
 581      * @param data the payload data to persist
 582      * @param batchHint if true, an attempt is made to delay immediate replication and batch the payload with
 583      *        subsequent payloads for efficiency. Otherwise the payload is immediately replicated.
 584      */
 585     protected final void persistData(final ActorRef clientActor, final Identifier identifier, final Payload data,
 586             final boolean batchHint) {
 587         ReplicatedLogEntry replicatedLogEntry = new SimpleReplicatedLogEntry(
 588             context.getReplicatedLog().lastIndex() + 1,
 589             context.getTermInformation().getCurrentTerm(), data);
 590         replicatedLogEntry.setPersistencePending(true);
 591
 592         LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 593
 594         final RaftActorContext raftContext = getRaftActorContext();
 595
 596         boolean wasAppended = replicatedLog().appendAndPersist(replicatedLogEntry, persistedLogEntry -> {
 597             // Clear the persistence pending flag in the log entry.
 598             persistedLogEntry.setPersistencePending(false);
 599
 600             if (!hasFollowers()) {
 601                 // Increment the Commit Index and the Last Applied values
 602                 raftContext.setCommitIndex(persistedLogEntry.getIndex());
 603                 raftContext.setLastApplied(persistedLogEntry.getIndex());
 604
 605                 // Apply the state immediately.
 606                 handleApplyState(new ApplyState(clientActor, identifier, persistedLogEntry));
 607
 608                 // Send a ApplyJournalEntries message so that we write the fact that we applied
 609                 // the state to durable storage
 610                 self().tell(new ApplyJournalEntries(persistedLogEntry.getIndex()), self());
 611
 612             } else {
 613                 context.getReplicatedLog().captureSnapshotIfReady(replicatedLogEntry);
 614
 615                 // Local persistence is complete so send the CheckConsensusReached message to the behavior (which
 616                 // normally should still be the leader) to check if consensus has now been reached in conjunction with
 617                 // follower replication.
 618                 getCurrentBehavior().handleMessage(getSelf(), CheckConsensusReached.INSTANCE);
 619             }
 620         }, true);
 621
 622         if (wasAppended && hasFollowers()) {
 623             // Send log entry for replication.
 624             getCurrentBehavior().handleMessage(getSelf(),
 625                 new Replicate(replicatedLogEntry.getIndex(), !batchHint, clientActor, identifier));
 626         }
 627     }
 628
 629     private ReplicatedLog replicatedLog() {
 630         return context.getReplicatedLog();
 631     }
 632
 633     protected String getId() {
 634         return context.getId();
 635     }
 636
 637     @VisibleForTesting
 638     void setCurrentBehavior(final RaftActorBehavior behavior) {
 639         context.setCurrentBehavior(behavior);
 640     }
 641
 642     protected RaftActorBehavior getCurrentBehavior() {
 643         return context.getCurrentBehavior();
 644     }
 645
 646     /**
 647      * Derived actors can call the isLeader method to check if the current
 648      * RaftActor is the Leader or not.
 649      *
 650      * @return true it this RaftActor is a Leader false otherwise
 651      */
 652     protected boolean isLeader() {
 653         return context.getId().equals(getCurrentBehavior().getLeaderId());
 654     }
 655
 656     protected final boolean isLeaderActive() {
 657         return getRaftState() != RaftState.IsolatedLeader && getRaftState() != RaftState.PreLeader
 658                 && !shuttingDown && !isLeadershipTransferInProgress();
 659     }
 660
 661     protected boolean isLeadershipTransferInProgress() {
 662         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
 663         return leadershipTransferInProgress != null && leadershipTransferInProgress.isTransferring();
 664     }
 665
 666     /**
 667      * Derived actor can call getLeader if they need a reference to the Leader.
 668      * This would be useful for example in forwarding a request to an actor
 669      * which is the leader
 670      *
 671      * @return A reference to the leader if known, null otherwise
 672      */
 673     public ActorSelection getLeader() {
 674         String leaderAddress = getLeaderAddress();
 675
 676         if (leaderAddress == null) {
 677             return null;
 678         }
 679
 680         return context.actorSelection(leaderAddress);
 681     }
 682
 683     /**
 684      * Returns the id of the current leader.
 685      *
 686      * @return the current leader's id
 687      */
 688     protected final String getLeaderId() {
 689         return getCurrentBehavior().getLeaderId();
 690     }
 691
 692     @VisibleForTesting
 693     protected final RaftState getRaftState() {
 694         return getCurrentBehavior().state();
 695     }
 696
 697     protected Long getCurrentTerm() {
 698         return context.getTermInformation().getCurrentTerm();
 699     }
 700
 701     protected RaftActorContext getRaftActorContext() {
 702         return context;
 703     }
 704
 705     protected void updateConfigParams(final ConfigParams configParams) {
 706
 707         // obtain the RaftPolicy for oldConfigParams and the updated one.
 708         String oldRaftPolicy = context.getConfigParams().getCustomRaftPolicyImplementationClass();
 709         String newRaftPolicy = configParams.getCustomRaftPolicyImplementationClass();
 710
 711         LOG.debug("{}: RaftPolicy used with prev.config {}, RaftPolicy used with newConfig {}", persistenceId(),
 712             oldRaftPolicy, newRaftPolicy);
 713         context.setConfigParams(configParams);
 714         if (!Objects.equals(oldRaftPolicy, newRaftPolicy)) {
 715             // The RaftPolicy was modified. If the current behavior is Follower then re-initialize to Follower
 716             // but transfer the previous leaderId so it doesn't immediately try to schedule an election. This
 717             // avoids potential disruption. Otherwise, switch to Follower normally.
 718             RaftActorBehavior behavior = getCurrentBehavior();
 719             if (behavior != null && behavior.state() == RaftState.Follower) {
 720                 String previousLeaderId = behavior.getLeaderId();
 721                 short previousLeaderPayloadVersion = behavior.getLeaderPayloadVersion();
 722
 723                 LOG.debug("{}: Re-initializing to Follower with previous leaderId {}", persistenceId(),
 724                         previousLeaderId);
 725
 726                 changeCurrentBehavior(new Follower(context, previousLeaderId, previousLeaderPayloadVersion));
 727             } else {
 728                 initializeBehavior();
 729             }
 730         }
 731     }
 732
 733     public final DataPersistenceProvider persistence() {
 734         return delegatingPersistenceProvider.getDelegate();
 735     }
 736
 737     public void setPersistence(final DataPersistenceProvider provider) {
 738         delegatingPersistenceProvider.setDelegate(provider);
 739     }
 740
 741     protected void setPersistence(final boolean persistent) {
 742         DataPersistenceProvider currentPersistence = persistence();
 743         if (persistent && (currentPersistence == null || !currentPersistence.isRecoveryApplicable())) {
 744             setPersistence(new PersistentDataProvider(this));
 745
 746             if (getCurrentBehavior() != null) {
 747                 LOG.info("{}: Persistence has been enabled - capturing snapshot", persistenceId());
 748                 captureSnapshot();
 749             }
 750         } else if (!persistent && (currentPersistence == null || currentPersistence.isRecoveryApplicable())) {
 751             setPersistence(new NonPersistentDataProvider(this) {
 752                 /*
 753                  * The way snapshotting works is,
 754                  * <ol>
 755                  * <li> RaftActor calls createSnapshot on the Shard
 756                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 757                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 758                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 759                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 760                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 761                  * </ol>
 762                  */
 763                 @Override
 764                 public void saveSnapshot(final Object object) {
 765                     // Make saving Snapshot successful
 766                     // Committing the snapshot here would end up calling commit in the creating state which would
 767                     // be a state violation. That's why now we send a message to commit the snapshot.
 768                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
 769                 }
 770             });
 771         }
 772     }
 773
 774     /**
 775      * setPeerAddress sets the address of a known peer at a later time.
 776      *
 777      * <p>
 778      * This is to account for situations where a we know that a peer
 779      * exists but we do not know an address up-front. This may also be used in
 780      * situations where a known peer starts off in a different location and we
 781      * need to change it's address
 782      *
 783      * <p>
 784      * Note that if the peerId does not match the list of peers passed to
 785      * this actor during construction an IllegalStateException will be thrown.
 786      */
 787     protected void setPeerAddress(final String peerId, final String peerAddress) {
 788         context.setPeerAddress(peerId, peerAddress);
 789     }
 790
 791     /**
 792      * The applyState method will be called by the RaftActor when some data
 793      * needs to be applied to the actor's state.
 794      *
 795      * @param clientActor A reference to the client who sent this message. This
 796      *                    is the same reference that was passed to persistData
 797      *                    by the derived actor. clientActor may be null when
 798      *                    the RaftActor is behaving as a follower or during
 799      *                    recovery.
 800      * @param identifier  The identifier of the persisted data. This is also
 801      *                    the same identifier that was passed to persistData by
 802      *                    the derived actor. identifier may be null when
 803      *                    the RaftActor is behaving as a follower or during
 804      *                    recovery
 805      * @param data        A piece of data that was persisted by the persistData call.
 806      *                    This should NEVER be null.
 807      */
 808     protected abstract void applyState(ActorRef clientActor, Identifier identifier, Object data);
 809
 810     /**
 811      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
 812      */
 813     protected abstract @NonNull RaftActorRecoveryCohort getRaftActorRecoveryCohort();
 814
 815     /**
 816      * This method is called when recovery is complete.
 817      */
 818     protected abstract void onRecoveryComplete();
 819
 820     /**
 821      * Returns the RaftActorSnapshotCohort to participate in snapshot captures.
 822      */
 823     protected abstract @NonNull RaftActorSnapshotCohort getRaftActorSnapshotCohort();
 824
 825     /**
 826      * This method will be called by the RaftActor when the state of the
 827      * RaftActor changes. The derived actor can then use methods like
 828      * isLeader or getLeader to do something useful
 829      */
 830     protected abstract void onStateChanged();
 831
 832     /**
 833      * Notifier Actor for this RaftActor to notify when a role change happens.
 834      *
 835      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 836      */
 837     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 838
 839     /**
 840      * This method is called on the leader when a voting change operation completes.
 841      */
 842     protected void onVotingStateChangeComplete() {
 843     }
 844
 845     /**
 846      * This method is called prior to operations such as leadership transfer and actor shutdown when the leader
 847      * must pause or stop its duties. This method allows derived classes to gracefully pause or finish current
 848      * work prior to performing the operation. On completion of any work, the run method must be called on the
 849      * given Runnable to proceed with the given operation. <b>Important:</b> the run method must be called on
 850      * this actor's thread dispatcher as as it modifies internal state.
 851      *
 852      * <p>
 853      * The default implementation immediately runs the operation.
 854      *
 855      * @param operation the operation to run
 856      */
 857     protected void pauseLeader(final Runnable operation) {
 858         operation.run();
 859     }
 860
 861     /**
 862      * This method is invoked when the actions hooked to the leader becoming paused failed to execute and the leader
 863      * should resume normal operations.
 864      *
 865      * <p>
 866      * Note this method can be invoked even before the operation supplied to {@link #pauseLeader(Runnable)} is invoked.
 867      */
 868     protected void unpauseLeader() {
 869
 870     }
 871
 872     protected void onLeaderChanged(final String oldLeader, final String newLeader) {
 873     }
 874
 875     private String getLeaderAddress() {
 876         if (isLeader()) {
 877             return getSelf().path().toString();
 878         }
 879         String leaderId = getLeaderId();
 880         if (leaderId == null) {
 881             return null;
 882         }
 883         String peerAddress = context.getPeerAddress(leaderId);
 884         LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}", persistenceId(), leaderId, peerAddress);
 885
 886         return peerAddress;
 887     }
 888
 889     protected boolean hasFollowers() {
 890         return getRaftActorContext().hasFollowers();
 891     }
 892
 893     private void captureSnapshot() {
 894         SnapshotManager snapshotManager = context.getSnapshotManager();
 895
 896         if (!snapshotManager.isCapturing()) {
 897             final long idx = getCurrentBehavior().getReplicatedToAllIndex();
 898             LOG.debug("Take a snapshot of current state. lastReplicatedLog is {} and replicatedToAllIndex is {}",
 899                 replicatedLog().last(), idx);
 900
 901             snapshotManager.captureWithForcedTrim(replicatedLog().last(), idx);
 902         }
 903     }
 904
 905     /**
 906      * Switch this member to non-voting status. This is a no-op for all behaviors except when we are the leader,
 907      * in which case we need to step down.
 908      */
 909     void becomeNonVoting() {
 910         if (isLeader()) {
 911             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
 912                 @Override
 913                 public void onSuccess(final ActorRef raftActorRef) {
 914                     LOG.debug("{}: leader transfer succeeded after change to non-voting", persistenceId());
 915                     ensureFollowerState();
 916                 }
 917
 918                 @Override
 919                 public void onFailure(final ActorRef raftActorRef) {
 920                     LOG.debug("{}: leader transfer failed after change to non-voting", persistenceId());
 921                     ensureFollowerState();
 922                 }
 923
 924                 private void ensureFollowerState() {
 925                     // Whether or not leadership transfer succeeded, we have to step down as leader and
 926                     // switch to Follower so ensure that.
 927                     if (getRaftState() != RaftState.Follower) {
 928                         initializeBehavior();
 929                     }
 930                 }
 931             }, null, RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
 932         }
 933     }
 934
 935     /**
 936      * A point-in-time capture of {@link RaftActorBehavior} state critical for transitioning between behaviors.
 937      */
 938     private abstract static class BehaviorState implements Immutable {
 939         @Nullable abstract RaftActorBehavior getBehavior();
 940
 941         @Nullable abstract String getLastValidLeaderId();
 942
 943         @Nullable abstract String getLastLeaderId();
 944
 945         abstract short getLeaderPayloadVersion();
 946     }
 947
 948     /**
 949      * A {@link BehaviorState} corresponding to non-null {@link RaftActorBehavior} state.
 950      */
 951     private static final class SimpleBehaviorState extends BehaviorState {
 952         private final RaftActorBehavior behavior;
 953         private final String lastValidLeaderId;
 954         private final String lastLeaderId;
 955         private final short leaderPayloadVersion;
 956
 957         SimpleBehaviorState(final String lastValidLeaderId, final String lastLeaderId,
 958                 final RaftActorBehavior behavior) {
 959             this.lastValidLeaderId = lastValidLeaderId;
 960             this.lastLeaderId = lastLeaderId;
 961             this.behavior = requireNonNull(behavior);
 962             leaderPayloadVersion = behavior.getLeaderPayloadVersion();
 963         }
 964
 965         @Override
 966         RaftActorBehavior getBehavior() {
 967             return behavior;
 968         }
 969
 970         @Override
 971         String getLastValidLeaderId() {
 972             return lastValidLeaderId;
 973         }
 974
 975         @Override
 976         short getLeaderPayloadVersion() {
 977             return leaderPayloadVersion;
 978         }
 979
 980         @Override
 981         String getLastLeaderId() {
 982             return lastLeaderId;
 983         }
 984     }
 985
 986     /**
 987      * Class tracking behavior-related information, which we need to keep around and pass across behavior switches.
 988      * An instance is created for each RaftActor. It has two functions:
 989      * - it keeps track of the last leader ID we have encountered since we have been created
 990      * - it creates state capture needed to transition from one behavior to the next
 991      */
 992     private static final class BehaviorStateTracker {
 993         /**
 994          * A {@link BehaviorState} corresponding to null {@link RaftActorBehavior} state. Since null behavior is only
 995          * allowed before we receive the first message, we know the leader ID to be null.
 996          */
 997         private static final BehaviorState NULL_BEHAVIOR_STATE = new BehaviorState() {
 998             @Override
 999             RaftActorBehavior getBehavior() {
1000                 return null;
1001             }
1002
1003             @Override
1004             String getLastValidLeaderId() {
1005                 return null;
1006             }
1007
1008             @Override
1009             short getLeaderPayloadVersion() {
1010                 return -1;
1011             }
1012
1013             @Override
1014             String getLastLeaderId() {
1015                 return null;
1016             }
1017         };
1018
1019         private String lastValidLeaderId;
1020         private String lastLeaderId;
1021
1022         BehaviorState capture(final RaftActorBehavior behavior) {
1023             if (behavior == null) {
1024                 verify(lastValidLeaderId == null, "Null behavior with non-null last leader");
1025                 return NULL_BEHAVIOR_STATE;
1026             }
1027
1028             lastLeaderId = behavior.getLeaderId();
1029             if (lastLeaderId != null) {
1030                 lastValidLeaderId = lastLeaderId;
1031             }
1032
1033             return new SimpleBehaviorState(lastValidLeaderId, lastLeaderId, behavior);
1034         }
1035     }
1036 }