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