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