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

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8
   9 package org.opendaylight.controller.cluster.raft.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.actor.Address;
  14 import akka.cluster.Cluster;
  15 import akka.cluster.ClusterEvent.CurrentClusterState;
  16 import akka.cluster.Member;
  17 import akka.cluster.MemberStatus;
  18 import akka.japi.Procedure;
  19 import com.google.common.annotations.VisibleForTesting;
  20 import com.google.common.base.Stopwatch;
  21 import java.io.IOException;
  22 import java.util.ArrayList;
  23 import java.util.List;
  24 import java.util.Optional;
  25 import java.util.Set;
  26 import java.util.concurrent.TimeUnit;
  27 import java.util.concurrent.atomic.AtomicBoolean;
  28 import javax.annotation.Nullable;
  29 import org.opendaylight.controller.cluster.messaging.MessageAssembler;
  30 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  31 import org.opendaylight.controller.cluster.raft.RaftState;
  32 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  33 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  34 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  35 import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
  36 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  37 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  38 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  39 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  40 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  41 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  42 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  43 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  44 import org.opendaylight.controller.cluster.raft.persisted.Snapshot;
  45
  46 /**
  47  * The behavior of a RaftActor in the Follower raft state.
  48  * <ul>
  49  * <li> Respond to RPCs from candidates and leaders
  50  * <li> If election timeout elapses without receiving AppendEntries
  51  * RPC from current leader or granting vote to candidate:
  52  * convert to candidate
  53  * </ul>
  54  */
  55 public class Follower extends AbstractRaftActorBehavior {
  56     private static final long MAX_ELECTION_TIMEOUT_FACTOR = 18;
  57
  58     private final SyncStatusTracker initialSyncStatusTracker;
  59
  60     private final MessageAssembler appendEntriesMessageAssembler;
  61
  62     private final Stopwatch lastLeaderMessageTimer = Stopwatch.createStarted();
  63     private SnapshotTracker snapshotTracker = null;
  64     private String leaderId;
  65     private short leaderPayloadVersion;
  66
  67     public Follower(final RaftActorContext context) {
  68         this(context, null, (short)-1);
  69     }
  70
  71     public Follower(final RaftActorContext context, final String initialLeaderId,
  72             final short initialLeaderPayloadVersion) {
  73         super(context, RaftState.Follower);
  74         this.leaderId = initialLeaderId;
  75         this.leaderPayloadVersion = initialLeaderPayloadVersion;
  76
  77         initialSyncStatusTracker = new SyncStatusTracker(context.getActor(), getId(), context.getConfigParams()
  78             .getSyncIndexThreshold());
  79
  80         appendEntriesMessageAssembler = MessageAssembler.builder().logContext(logName())
  81                 .filedBackedStreamFactory(context.getFileBackedOutputStreamFactory())
  82                 .assembledMessageCallback((message, sender) -> handleMessage(sender, message)).build();
  83
  84         if (context.getPeerIds().isEmpty() && getLeaderId() == null) {
  85             actor().tell(TimeoutNow.INSTANCE, actor());
  86         } else {
  87             scheduleElection(electionDuration());
  88         }
  89     }
  90
  91     @Override
  92     public final String getLeaderId() {
  93         return leaderId;
  94     }
  95
  96     @VisibleForTesting
  97     protected final void setLeaderId(@Nullable final String leaderId) {
  98         this.leaderId = leaderId;
  99     }
 100
 101     @Override
 102     public short getLeaderPayloadVersion() {
 103         return leaderPayloadVersion;
 104     }
 105
 106     @VisibleForTesting
 107     protected final void setLeaderPayloadVersion(final short leaderPayloadVersion) {
 108         this.leaderPayloadVersion = leaderPayloadVersion;
 109     }
 110
 111     private void restartLastLeaderMessageTimer() {
 112         if (lastLeaderMessageTimer.isRunning()) {
 113             lastLeaderMessageTimer.reset();
 114         }
 115
 116         lastLeaderMessageTimer.start();
 117     }
 118
 119     private boolean isLogEntryPresent(final long index) {
 120         if (context.getReplicatedLog().isInSnapshot(index)) {
 121             return true;
 122         }
 123
 124         ReplicatedLogEntry entry = context.getReplicatedLog().get(index);
 125         return entry != null;
 126
 127     }
 128
 129     private void updateInitialSyncStatus(final long currentLeaderCommit, final String newLeaderId) {
 130         initialSyncStatusTracker.update(newLeaderId, currentLeaderCommit, context.getCommitIndex());
 131     }
 132
 133     @Override
 134     protected RaftActorBehavior handleAppendEntries(final ActorRef sender, final AppendEntries appendEntries) {
 135
 136         int numLogEntries = appendEntries.getEntries().size();
 137         if (log.isTraceEnabled()) {
 138             log.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
 139         } else if (log.isDebugEnabled() && numLogEntries > 0) {
 140             log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 141         }
 142
 143         // TODO : Refactor this method into a bunch of smaller methods
 144         // to make it easier to read. Before refactoring ensure tests
 145         // cover the code properly
 146
 147         if (snapshotTracker != null && !snapshotTracker.getLeaderId().equals(appendEntries.getLeaderId())) {
 148             log.debug("{}: snapshot install is in progress but the prior snapshot leaderId {} does not match the "
 149                 + "AppendEntries leaderId {}", logName(), snapshotTracker.getLeaderId(), appendEntries.getLeaderId());
 150             closeSnapshotTracker();
 151         }
 152
 153         if (snapshotTracker != null || context.getSnapshotManager().isApplying()) {
 154             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
 155             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 156                     lastIndex(), lastTerm(), context.getPayloadVersion());
 157
 158             log.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
 159             sender.tell(reply, actor());
 160
 161             return this;
 162         }
 163
 164         // If we got here then we do appear to be talking to the leader
 165         leaderId = appendEntries.getLeaderId();
 166         leaderPayloadVersion = appendEntries.getPayloadVersion();
 167
 168         // First check if the logs are in sync or not
 169         long lastIndex = lastIndex();
 170
 171         if (isOutOfSync(appendEntries)) {
 172             // We found that the log was out of sync so just send a negative
 173             // reply and return
 174
 175             final AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 176                     lastTerm(), context.getPayloadVersion());
 177
 178             log.info("{}: Follower is out-of-sync so sending negative reply: {}", logName(), reply);
 179             updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 180             sender.tell(reply, actor());
 181             return this;
 182         }
 183
 184         if (numLogEntries > 0) {
 185             log.debug("{}: Number of entries to be appended = {}", logName(), numLogEntries);
 186
 187             // 3. If an existing entry conflicts with a new one (same index
 188             // but different terms), delete the existing entry and all that
 189             // follow it (§5.3)
 190             int addEntriesFrom = 0;
 191             if (context.getReplicatedLog().size() > 0) {
 192
 193                 // Find the entry up until the one that is not in the follower's log
 194                 for (int i = 0;i < numLogEntries; i++, addEntriesFrom++) {
 195                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 196
 197                     if (!isLogEntryPresent(matchEntry.getIndex())) {
 198                         // newEntry not found in the log
 199                         break;
 200                     }
 201
 202                     long existingEntryTerm = getLogEntryTerm(matchEntry.getIndex());
 203
 204                     log.debug("{}: matchEntry {} is present: existingEntryTerm: {}", logName(), matchEntry,
 205                             existingEntryTerm);
 206
 207                     // existingEntryTerm == -1 means it's in the snapshot and not in the log. We don't know
 208                     // what the term was so we'll assume it matches.
 209                     if (existingEntryTerm == -1 || existingEntryTerm == matchEntry.getTerm()) {
 210                         continue;
 211                     }
 212
 213                     if (!context.getRaftPolicy().applyModificationToStateBeforeConsensus()) {
 214
 215                         log.info("{}: Removing entries from log starting at {}", logName(), matchEntry.getIndex());
 216
 217                         // Entries do not match so remove all subsequent entries
 218                         if (!context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex())) {
 219                             // Could not remove the entries - this means the matchEntry index must be in the
 220                             // snapshot and not the log. In this case the prior entries are part of the state
 221                             // so we must send back a reply to force a snapshot to completely re-sync the
 222                             // follower's log and state.
 223
 224                             log.info("{}: Could not remove entries - sending reply to force snapshot", logName());
 225                             updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 226                             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 227                                     lastTerm(), context.getPayloadVersion(), true), actor());
 228                             return this;
 229                         }
 230
 231                         break;
 232                     } else {
 233                         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 234                         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 235                                 lastTerm(), context.getPayloadVersion(), true), actor());
 236                         return this;
 237                     }
 238                 }
 239             }
 240
 241             lastIndex = lastIndex();
 242             log.debug("{}: After cleanup, lastIndex: {}, entries to be added from: {}", logName(),
 243                     lastIndex, addEntriesFrom);
 244
 245             // When persistence successfully completes for each new log entry appended, we need to determine if we
 246             // should capture a snapshot to compact the persisted log. shouldCaptureSnapshot tracks whether or not
 247             // one of the log entries has exceeded the log size threshold whereby a snapshot should be taken. However
 248             // we don't initiate the snapshot at that log entry but rather after the last log entry has been persisted.
 249             // This is done because subsequent log entries after the one that tripped the threshold may have been
 250             // applied to the state already, as the persistence callback occurs async, and we want those entries
 251             // purged from the persisted log as well.
 252             final AtomicBoolean shouldCaptureSnapshot = new AtomicBoolean(false);
 253             final Procedure<ReplicatedLogEntry> appendAndPersistCallback = logEntry -> {
 254                 final List<ReplicatedLogEntry> entries = appendEntries.getEntries();
 255                 final ReplicatedLogEntry lastEntryToAppend = entries.get(entries.size() - 1);
 256                 if (shouldCaptureSnapshot.get() && logEntry == lastEntryToAppend) {
 257                     context.getSnapshotManager().capture(context.getReplicatedLog().last(), getReplicatedToAllIndex());
 258                 }
 259             };
 260
 261             // 4. Append any new entries not already in the log
 262             for (int i = addEntriesFrom; i < numLogEntries; i++) {
 263                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 264
 265                 log.debug("{}: Append entry to log {}", logName(), entry.getData());
 266
 267                 context.getReplicatedLog().appendAndPersist(entry, appendAndPersistCallback, false);
 268
 269                 shouldCaptureSnapshot.compareAndSet(false,
 270                         context.getReplicatedLog().shouldCaptureSnapshot(entry.getIndex()));
 271
 272                 if (entry.getData() instanceof ServerConfigurationPayload) {
 273                     context.updatePeerIds((ServerConfigurationPayload)entry.getData());
 274                 }
 275             }
 276
 277             log.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 278         }
 279
 280         // 5. If leaderCommit > commitIndex, set commitIndex =
 281         // min(leaderCommit, index of last new entry)
 282
 283         lastIndex = lastIndex();
 284         long prevCommitIndex = context.getCommitIndex();
 285
 286         if (appendEntries.getLeaderCommit() > prevCommitIndex) {
 287             context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 288         }
 289
 290         if (prevCommitIndex != context.getCommitIndex()) {
 291             log.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 292         }
 293
 294         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 295                 lastIndex, lastTerm(), context.getPayloadVersion());
 296
 297         if (log.isTraceEnabled()) {
 298             log.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 299         } else if (log.isDebugEnabled() && numLogEntries > 0) {
 300             log.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 301         }
 302
 303         // Reply to the leader before applying any previous state so as not to hold up leader consensus.
 304         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 305         sender.tell(reply, actor());
 306
 307         // If commitIndex > lastApplied: increment lastApplied, apply
 308         // log[lastApplied] to state machine (§5.3)
 309         // check if there are any entries to be applied. last-applied can be equal to last-index
 310         if (appendEntries.getLeaderCommit() > context.getLastApplied()
 311                 && context.getLastApplied() < lastIndex) {
 312             if (log.isDebugEnabled()) {
 313                 log.debug("{}: applyLogToStateMachine, appendEntries.getLeaderCommit(): {}, "
 314                         + "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 315                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 316             }
 317
 318             applyLogToStateMachine(appendEntries.getLeaderCommit());
 319         }
 320
 321         if (!context.getSnapshotManager().isCapturing()) {
 322             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 323         }
 324
 325         appendEntriesMessageAssembler.checkExpiredAssembledMessageState();
 326
 327         return this;
 328     }
 329
 330     private boolean isOutOfSync(final AppendEntries appendEntries) {
 331
 332         final long lastIndex = lastIndex();
 333         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 334
 335             // The follower's log is out of sync because the leader does have an entry at prevLogIndex and this
 336             // follower has no entries in it's log.
 337
 338             log.info("{}: The followers log is empty and the senders prevLogIndex is {}", logName(),
 339                 appendEntries.getPrevLogIndex());
 340             return true;
 341         }
 342
 343         if (lastIndex > -1) {
 344             if (isLogEntryPresent(appendEntries.getPrevLogIndex())) {
 345                 final long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 346                 if (prevLogTerm != appendEntries.getPrevLogTerm()) {
 347
 348                     // The follower's log is out of sync because the Leader's prevLogIndex entry does exist
 349                     // in the follower's log but it has a different term in it
 350
 351                     log.info("{}: The prevLogIndex {} was found in the log but the term {} is not equal to the append "
 352                             + "entries prevLogTerm {} - lastIndex: {}, snapshotIndex: {}", logName(),
 353                             appendEntries.getPrevLogIndex(), prevLogTerm, appendEntries.getPrevLogTerm(), lastIndex,
 354                             context.getReplicatedLog().getSnapshotIndex());
 355                     return true;
 356                 }
 357             } else if (appendEntries.getPrevLogIndex() != -1) {
 358
 359                 // The follower's log is out of sync because the Leader's prevLogIndex entry was not found in it's log
 360
 361                 log.info("{}: The log is not empty but the prevLogIndex {} was not found in it - lastIndex: {}, "
 362                         + "snapshotIndex: {}", logName(), appendEntries.getPrevLogIndex(), lastIndex,
 363                         context.getReplicatedLog().getSnapshotIndex());
 364                 return true;
 365             }
 366         }
 367
 368         if (appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 369                 && appendEntries.getReplicatedToAllIndex() != -1) {
 370             if (!isLogEntryPresent(appendEntries.getReplicatedToAllIndex())) {
 371                 // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
 372                 // the previous entry in it's in-memory journal
 373
 374                 log.info("{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the "
 375                         + "in-memory journal", logName(), appendEntries.getReplicatedToAllIndex());
 376                 return true;
 377             }
 378
 379             final List<ReplicatedLogEntry> entries = appendEntries.getEntries();
 380             if (entries.size() > 0 && !isLogEntryPresent(entries.get(0).getIndex() - 1)) {
 381                 log.info("{}: Cannot append entries because the calculated previousIndex {} was not found in the "
 382                         + "in-memory journal", logName(), entries.get(0).getIndex() - 1);
 383                 return true;
 384             }
 385         }
 386
 387         return false;
 388     }
 389
 390     @Override
 391     protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
 392         final AppendEntriesReply appendEntriesReply) {
 393         return this;
 394     }
 395
 396     @Override
 397     protected RaftActorBehavior handleRequestVoteReply(final ActorRef sender,
 398         final RequestVoteReply requestVoteReply) {
 399         return this;
 400     }
 401
 402     @Override
 403     public RaftActorBehavior handleMessage(final ActorRef sender, final Object message) {
 404         if (message instanceof ElectionTimeout || message instanceof TimeoutNow) {
 405             return handleElectionTimeout(message);
 406         }
 407
 408         if (appendEntriesMessageAssembler.handleMessage(message, actor())) {
 409             return this;
 410         }
 411
 412         if (!(message instanceof RaftRPC)) {
 413             // The rest of the processing requires the message to be a RaftRPC
 414             return null;
 415         }
 416
 417         final RaftRPC rpc = (RaftRPC) message;
 418         // If RPC request or response contains term T > currentTerm:
 419         // set currentTerm = T, convert to follower (§5.1)
 420         // This applies to all RPC messages and responses
 421         if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 422             log.info("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 423                 logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 424
 425             context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 426         }
 427
 428         if (rpc instanceof InstallSnapshot) {
 429             handleInstallSnapshot(sender, (InstallSnapshot) rpc);
 430             restartLastLeaderMessageTimer();
 431             scheduleElection(electionDuration());
 432             return this;
 433         }
 434
 435         if (!(rpc instanceof RequestVote) || canGrantVote((RequestVote) rpc)) {
 436             restartLastLeaderMessageTimer();
 437             scheduleElection(electionDuration());
 438         }
 439
 440         return super.handleMessage(sender, rpc);
 441     }
 442
 443     private RaftActorBehavior handleElectionTimeout(final Object message) {
 444         // If the message is ElectionTimeout, verify we haven't actually seen a message from the leader
 445         // during the election timeout interval. It may that the election timer expired b/c this actor
 446         // was busy and messages got delayed, in which case leader messages would be backed up in the
 447         // queue but would be processed before the ElectionTimeout message and thus would restart the
 448         // lastLeaderMessageTimer.
 449         long lastLeaderMessageInterval = lastLeaderMessageTimer.elapsed(TimeUnit.MILLISECONDS);
 450         long electionTimeoutInMillis = context.getConfigParams().getElectionTimeOutInterval().toMillis();
 451         boolean noLeaderMessageReceived = !lastLeaderMessageTimer.isRunning()
 452                 || lastLeaderMessageInterval >= electionTimeoutInMillis;
 453
 454         if (canStartElection()) {
 455             if (message instanceof TimeoutNow) {
 456                 log.debug("{}: Received TimeoutNow - switching to Candidate", logName());
 457                 return internalSwitchBehavior(RaftState.Candidate);
 458             } else if (noLeaderMessageReceived) {
 459                 // Check the cluster state to see if the leader is known to be up before we go to Candidate.
 460                 // However if we haven't heard from the leader in a long time even though the cluster state
 461                 // indicates it's up then something is wrong - leader might be stuck indefinitely - so switch
 462                 // to Candidate,
 463                 long maxElectionTimeout = electionTimeoutInMillis * MAX_ELECTION_TIMEOUT_FACTOR;
 464                 if (isLeaderAvailabilityKnown() && lastLeaderMessageInterval < maxElectionTimeout) {
 465                     log.debug("{}: Received ElectionTimeout but leader appears to be available", logName());
 466                     scheduleElection(electionDuration());
 467                 } else {
 468                     log.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 469                     return internalSwitchBehavior(RaftState.Candidate);
 470                 }
 471             } else {
 472                 log.debug("{}: Received ElectionTimeout but lastLeaderMessageInterval {} < election timeout {}",
 473                         logName(), lastLeaderMessageInterval, context.getConfigParams().getElectionTimeOutInterval());
 474                 scheduleElection(electionDuration());
 475             }
 476         } else if (message instanceof ElectionTimeout) {
 477             if (noLeaderMessageReceived) {
 478                 setLeaderId(null);
 479             }
 480
 481             scheduleElection(electionDuration());
 482         }
 483
 484         return this;
 485     }
 486
 487     private boolean isLeaderAvailabilityKnown() {
 488         if (leaderId == null) {
 489             return false;
 490         }
 491
 492         Optional<Cluster> cluster = context.getCluster();
 493         if (!cluster.isPresent()) {
 494             return false;
 495         }
 496
 497         ActorSelection leaderActor = context.getPeerActorSelection(leaderId);
 498         if (leaderActor == null) {
 499             return false;
 500         }
 501
 502         Address leaderAddress = leaderActor.anchorPath().address();
 503
 504         CurrentClusterState state = cluster.get().state();
 505         Set<Member> unreachable = state.getUnreachable();
 506
 507         log.debug("{}: Checking for leader {} in the cluster unreachable set {}", logName(), leaderAddress,
 508                 unreachable);
 509
 510         for (Member m: unreachable) {
 511             if (leaderAddress.equals(m.address())) {
 512                 log.info("{}: Leader {} is unreachable", logName(), leaderAddress);
 513                 return false;
 514             }
 515         }
 516
 517         for (Member m: state.getMembers()) {
 518             if (leaderAddress.equals(m.address())) {
 519                 if (m.status() == MemberStatus.up() || m.status() == MemberStatus.weaklyUp()) {
 520                     log.debug("{}: Leader {} cluster status is {} - leader is available", logName(),
 521                             leaderAddress, m.status());
 522                     return true;
 523                 } else {
 524                     log.debug("{}: Leader {} cluster status is {} - leader is unavailable", logName(),
 525                             leaderAddress, m.status());
 526                     return false;
 527                 }
 528             }
 529         }
 530
 531         log.debug("{}: Leader {} not found in the cluster member set", logName(), leaderAddress);
 532
 533         return false;
 534     }
 535
 536     private void handleInstallSnapshot(final ActorRef sender, final InstallSnapshot installSnapshot) {
 537
 538         log.debug("{}: handleInstallSnapshot: {}", logName(), installSnapshot);
 539
 540         leaderId = installSnapshot.getLeaderId();
 541
 542         if (snapshotTracker == null) {
 543             snapshotTracker = new SnapshotTracker(log, installSnapshot.getTotalChunks(), installSnapshot.getLeaderId(),
 544                     context);
 545         }
 546
 547         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 548
 549         try {
 550             final InstallSnapshotReply reply = new InstallSnapshotReply(
 551                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 552
 553             if (snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 554                     installSnapshot.getLastChunkHashCode())) {
 555
 556                 log.info("{}: Snapshot installed from leader: {}", logName(), installSnapshot.getLeaderId());
 557
 558                 Snapshot snapshot = Snapshot.create(
 559                         context.getSnapshotManager().convertSnapshot(snapshotTracker.getSnapshotBytes()),
 560                         new ArrayList<>(),
 561                         installSnapshot.getLastIncludedIndex(),
 562                         installSnapshot.getLastIncludedTerm(),
 563                         installSnapshot.getLastIncludedIndex(),
 564                         installSnapshot.getLastIncludedTerm(),
 565                         context.getTermInformation().getCurrentTerm(),
 566                         context.getTermInformation().getVotedFor(),
 567                         installSnapshot.getServerConfig().orNull());
 568
 569                 ApplySnapshot.Callback applySnapshotCallback = new ApplySnapshot.Callback() {
 570                     @Override
 571                     public void onSuccess() {
 572                         log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 573
 574                         sender.tell(reply, actor());
 575                     }
 576
 577                     @Override
 578                     public void onFailure() {
 579                         sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(), -1, false), actor());
 580                     }
 581                 };
 582
 583                 actor().tell(new ApplySnapshot(snapshot, applySnapshotCallback), actor());
 584
 585                 closeSnapshotTracker();
 586             } else {
 587                 log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 588
 589                 sender.tell(reply, actor());
 590             }
 591         } catch (IOException e) {
 592             log.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 593
 594             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 595                     -1, false), actor());
 596
 597             closeSnapshotTracker();
 598         }
 599     }
 600
 601     private void closeSnapshotTracker() {
 602         if (snapshotTracker != null) {
 603             snapshotTracker.close();
 604             snapshotTracker = null;
 605         }
 606     }
 607
 608     @Override
 609     public void close() {
 610         closeSnapshotTracker();
 611         stopElection();
 612         appendEntriesMessageAssembler.close();
 613     }
 614
 615     @VisibleForTesting
 616     SnapshotTracker getSnapshotTracker() {
 617         return snapshotTracker;
 618     }
 619 }