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 com.google.common.io.ByteSource;
  22 import java.io.IOException;
  23 import java.util.ArrayList;
  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 int SYNC_THRESHOLD = 10;
  56
  57     private static final long MAX_ELECTION_TIMEOUT_FACTOR = 18;
  58
  59     private final SyncStatusTracker initialSyncStatusTracker;
  60
  61     private final Stopwatch lastLeaderMessageTimer = Stopwatch.createStarted();
  62     private SnapshotTracker snapshotTracker = null;
  63     private String leaderId;
  64     private short leaderPayloadVersion;
  65
  66     public Follower(RaftActorContext context) {
  67         this(context, null, (short)-1);
  68     }
  69
  70     public Follower(RaftActorContext context, String initialLeaderId, short initialLeaderPayloadVersion) {
  71         super(context, RaftState.Follower);
  72         this.leaderId = initialLeaderId;
  73         this.leaderPayloadVersion = initialLeaderPayloadVersion;
  74
  75         initialSyncStatusTracker = new SyncStatusTracker(context.getActor(), getId(), SYNC_THRESHOLD);
  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(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(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(long currentLeaderCommit, String newLeaderId) {
 123         initialSyncStatusTracker.update(newLeaderId, currentLeaderCommit, context.getCommitIndex());
 124     }
 125
 126     @Override
 127     protected RaftActorBehavior handleAppendEntries(ActorRef sender, AppendEntries appendEntries) {
 128
 129         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
 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             snapshotTracker = null;
 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         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 162         // First check if the logs are in sync or not
 163         long lastIndex = lastIndex();
 164
 165         if (isOutOfSync(appendEntries)) {
 166             // We found that the log was out of sync so just send a negative
 167             // reply and return
 168
 169             log.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
 170                         logName(), lastIndex, lastTerm());
 171
 172             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 173                     lastTerm(), context.getPayloadVersion()), actor());
 174             return this;
 175         }
 176
 177         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
 178
 179             log.debug("{}: Number of entries to be appended = {}", logName(),
 180                         appendEntries.getEntries().size());
 181
 182             // 3. If an existing entry conflicts with a new one (same index
 183             // but different terms), delete the existing entry and all that
 184             // follow it (§5.3)
 185             int addEntriesFrom = 0;
 186             if (context.getReplicatedLog().size() > 0) {
 187
 188                 // Find the entry up until the one that is not in the follower's log
 189                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 190                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 191
 192                     if (!isLogEntryPresent(matchEntry.getIndex())) {
 193                         // newEntry not found in the log
 194                         break;
 195                     }
 196
 197                     long existingEntryTerm = getLogEntryTerm(matchEntry.getIndex());
 198
 199                     log.debug("{}: matchEntry {} is present: existingEntryTerm: {}", logName(), matchEntry,
 200                             existingEntryTerm);
 201
 202                     // existingEntryTerm == -1 means it's in the snapshot and not in the log. We don't know
 203                     // what the term was so we'll assume it matches.
 204                     if (existingEntryTerm == -1 || existingEntryTerm == matchEntry.getTerm()) {
 205                         continue;
 206                     }
 207
 208                     if (!context.getRaftPolicy().applyModificationToStateBeforeConsensus()) {
 209
 210                         log.debug("{}: Removing entries from log starting at {}", logName(),
 211                                 matchEntry.getIndex());
 212
 213                         // Entries do not match so remove all subsequent entries
 214                         if (!context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex())) {
 215                             // Could not remove the entries - this means the matchEntry index must be in the
 216                             // snapshot and not the log. In this case the prior entries are part of the state
 217                             // so we must send back a reply to force a snapshot to completely re-sync the
 218                             // follower's log and state.
 219
 220                             log.debug("{}: Could not remove entries - sending reply to force snapshot", logName());
 221                             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 222                                     lastTerm(), context.getPayloadVersion(), true), actor());
 223                             return this;
 224                         }
 225
 226                         break;
 227                     } else {
 228                         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 229                                 lastTerm(), context.getPayloadVersion(), true), actor());
 230                         return this;
 231                     }
 232                 }
 233             }
 234
 235             lastIndex = lastIndex();
 236             log.debug("{}: After cleanup, lastIndex: {}, entries to be added from: {}", logName(),
 237                     lastIndex, addEntriesFrom);
 238
 239             // When persistence successfully completes for each new log entry appended, we need to determine if we
 240             // should capture a snapshot to compact the persisted log. shouldCaptureSnapshot tracks whether or not
 241             // one of the log entries has exceeded the log size threshold whereby a snapshot should be taken. However
 242             // we don't initiate the snapshot at that log entry but rather after the last log entry has been persisted.
 243             // This is done because subsequent log entries after the one that tripped the threshold may have been
 244             // applied to the state already, as the persistence callback occurs async, and we want those entries
 245             // purged from the persisted log as well.
 246             final AtomicBoolean shouldCaptureSnapshot = new AtomicBoolean(false);
 247             final Procedure<ReplicatedLogEntry> appendAndPersistCallback = logEntry -> {
 248                 final ReplicatedLogEntry lastEntryToAppend = appendEntries.getEntries().get(
 249                         appendEntries.getEntries().size() - 1);
 250                 if (shouldCaptureSnapshot.get() && logEntry == lastEntryToAppend) {
 251                     context.getSnapshotManager().capture(context.getReplicatedLog().last(), getReplicatedToAllIndex());
 252                 }
 253             };
 254
 255             // 4. Append any new entries not already in the log
 256             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
 257                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 258
 259                 log.debug("{}: Append entry to log {}", logName(), entry.getData());
 260
 261                 context.getReplicatedLog().appendAndPersist(entry, appendAndPersistCallback, false);
 262
 263                 shouldCaptureSnapshot.compareAndSet(false,
 264                         context.getReplicatedLog().shouldCaptureSnapshot(entry.getIndex()));
 265
 266                 if (entry.getData() instanceof ServerConfigurationPayload) {
 267                     context.updatePeerIds((ServerConfigurationPayload)entry.getData());
 268                 }
 269             }
 270
 271             log.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 272         }
 273
 274         // 5. If leaderCommit > commitIndex, set commitIndex =
 275         // min(leaderCommit, index of last new entry)
 276
 277         lastIndex = lastIndex();
 278         long prevCommitIndex = context.getCommitIndex();
 279
 280         if (appendEntries.getLeaderCommit() > prevCommitIndex) {
 281             context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 282         }
 283
 284         if (prevCommitIndex != context.getCommitIndex()) {
 285             log.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 286         }
 287
 288         // If commitIndex > lastApplied: increment lastApplied, apply
 289         // log[lastApplied] to state machine (§5.3)
 290         // check if there are any entries to be applied. last-applied can be equal to last-index
 291         if (appendEntries.getLeaderCommit() > context.getLastApplied()
 292                 && context.getLastApplied() < lastIndex) {
 293             if (log.isDebugEnabled()) {
 294                 log.debug("{}: applyLogToStateMachine, appendEntries.getLeaderCommit(): {},"
 295                         + "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 296                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 297             }
 298
 299             applyLogToStateMachine(appendEntries.getLeaderCommit());
 300         }
 301
 302         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 303             lastIndex, lastTerm(), context.getPayloadVersion());
 304
 305         if (log.isTraceEnabled()) {
 306             log.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 307         } else if (log.isDebugEnabled() && numLogEntries > 0) {
 308             log.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 309         }
 310
 311         sender.tell(reply, actor());
 312
 313         if (!context.getSnapshotManager().isCapturing()) {
 314             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 315         }
 316
 317         return this;
 318     }
 319
 320     private boolean isOutOfSync(AppendEntries appendEntries) {
 321
 322         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 323         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
 324         long lastIndex = lastIndex();
 325         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
 326         boolean outOfSync = true;
 327
 328         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 329
 330             // The follower's log is out of sync because the leader does have
 331             // an entry at prevLogIndex and this follower has no entries in
 332             // it's log.
 333
 334             log.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
 335                         logName(), appendEntries.getPrevLogIndex());
 336         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
 337
 338             // The follower's log is out of sync because the Leader's
 339             // prevLogIndex entry was not found in it's log
 340
 341             log.debug("{}: The log is not empty but the prevLogIndex {} was not found in it - "
 342                     + "lastIndex: {}, snapshotIndex: {}", logName(), appendEntries.getPrevLogIndex(), lastIndex,
 343                     context.getReplicatedLog().getSnapshotIndex());
 344         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
 345
 346             // The follower's log is out of sync because the Leader's
 347             // prevLogIndex entry does exist in the follower's log but it has
 348             // a different term in it
 349
 350             log.debug("{}: The prevLogIndex {} was found in the log but the term {} is not equal to the append entries"
 351                       + "prevLogTerm {} - lastIndex: {}, snapshotIndex: {}", logName(), appendEntries.getPrevLogIndex(),
 352                       prevLogTerm, appendEntries.getPrevLogTerm(), lastIndex,
 353                       context.getReplicatedLog().getSnapshotIndex());
 354         } else if (appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 355                 && appendEntries.getReplicatedToAllIndex() != -1
 356                 && !isLogEntryPresent(appendEntries.getReplicatedToAllIndex())) {
 357             // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
 358             // the previous entry in it's in-memory journal
 359
 360             log.debug("{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the"
 361                     + " in-memory journal", logName(), appendEntries.getReplicatedToAllIndex());
 362         } else if (appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 363                 && appendEntries.getReplicatedToAllIndex() != -1 && numLogEntries > 0
 364                 && !isLogEntryPresent(appendEntries.getEntries().get(0).getIndex() - 1)) {
 365             log.debug("{}: Cannot append entries because the calculated previousIndex {} was not found in the "
 366                     + " in-memory journal", logName(), appendEntries.getEntries().get(0).getIndex() - 1);
 367         } else {
 368             outOfSync = false;
 369         }
 370         return outOfSync;
 371     }
 372
 373     @Override
 374     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 375         AppendEntriesReply appendEntriesReply) {
 376         return this;
 377     }
 378
 379     @Override
 380     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 381         RequestVoteReply requestVoteReply) {
 382         return this;
 383     }
 384
 385     @Override
 386     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 387         if (message instanceof ElectionTimeout || message instanceof TimeoutNow) {
 388             return handleElectionTimeout(message);
 389         }
 390
 391         if (!(message instanceof RaftRPC)) {
 392             // The rest of the processing requires the message to be a RaftRPC
 393             return null;
 394         }
 395
 396         final RaftRPC rpc = (RaftRPC) message;
 397         // If RPC request or response contains term T > currentTerm:
 398         // set currentTerm = T, convert to follower (§5.1)
 399         // This applies to all RPC messages and responses
 400         if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 401             log.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 402                 logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 403
 404             context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 405         }
 406
 407         if (rpc instanceof InstallSnapshot) {
 408             handleInstallSnapshot(sender, (InstallSnapshot) rpc);
 409             restartLastLeaderMessageTimer();
 410             scheduleElection(electionDuration());
 411             return this;
 412         }
 413
 414         if (!(rpc instanceof RequestVote) || canGrantVote((RequestVote) rpc)) {
 415             restartLastLeaderMessageTimer();
 416             scheduleElection(electionDuration());
 417         }
 418
 419         return super.handleMessage(sender, rpc);
 420     }
 421
 422     private RaftActorBehavior handleElectionTimeout(Object message) {
 423         // If the message is ElectionTimeout, verify we haven't actually seen a message from the leader
 424         // during the election timeout interval. It may that the election timer expired b/c this actor
 425         // was busy and messages got delayed, in which case leader messages would be backed up in the
 426         // queue but would be processed before the ElectionTimeout message and thus would restart the
 427         // lastLeaderMessageTimer.
 428         long lastLeaderMessageInterval = lastLeaderMessageTimer.elapsed(TimeUnit.MILLISECONDS);
 429         long electionTimeoutInMillis = context.getConfigParams().getElectionTimeOutInterval().toMillis();
 430         boolean noLeaderMessageReceived = !lastLeaderMessageTimer.isRunning()
 431                 || lastLeaderMessageInterval >= electionTimeoutInMillis;
 432
 433         if (canStartElection()) {
 434             if (message instanceof TimeoutNow) {
 435                 log.debug("{}: Received TimeoutNow - switching to Candidate", logName());
 436                 return internalSwitchBehavior(RaftState.Candidate);
 437             } else if (noLeaderMessageReceived) {
 438                 // Check the cluster state to see if the leader is known to be up before we go to Candidate.
 439                 // However if we haven't heard from the leader in a long time even though the cluster state
 440                 // indicates it's up then something is wrong - leader might be stuck indefinitely - so switch
 441                 // to Candidate,
 442                 long maxElectionTimeout = electionTimeoutInMillis * MAX_ELECTION_TIMEOUT_FACTOR;
 443                 if (isLeaderAvailabilityKnown() && lastLeaderMessageInterval < maxElectionTimeout) {
 444                     log.debug("{}: Received ElectionTimeout but leader appears to be available", logName());
 445                     scheduleElection(electionDuration());
 446                 } else {
 447                     log.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 448                     return internalSwitchBehavior(RaftState.Candidate);
 449                 }
 450             } else {
 451                 log.debug("{}: Received ElectionTimeout but lastLeaderMessageInterval {} < election timeout {}",
 452                         logName(), lastLeaderMessageInterval, context.getConfigParams().getElectionTimeOutInterval());
 453                 scheduleElection(electionDuration());
 454             }
 455         } else if (message instanceof ElectionTimeout) {
 456             if (noLeaderMessageReceived) {
 457                 setLeaderId(null);
 458             }
 459
 460             scheduleElection(electionDuration());
 461         }
 462
 463         return this;
 464     }
 465
 466     private boolean isLeaderAvailabilityKnown() {
 467         if (leaderId == null) {
 468             return false;
 469         }
 470
 471         Optional<Cluster> cluster = context.getCluster();
 472         if (!cluster.isPresent()) {
 473             return false;
 474         }
 475
 476         ActorSelection leaderActor = context.getPeerActorSelection(leaderId);
 477         if (leaderActor == null) {
 478             return false;
 479         }
 480
 481         Address leaderAddress = leaderActor.anchorPath().address();
 482
 483         CurrentClusterState state = cluster.get().state();
 484         Set<Member> unreachable = state.getUnreachable();
 485
 486         log.debug("{}: Checking for leader {} in the cluster unreachable set {}", logName(), leaderAddress,
 487                 unreachable);
 488
 489         for (Member m: unreachable) {
 490             if (leaderAddress.equals(m.address())) {
 491                 log.info("{}: Leader {} is unreachable", logName(), leaderAddress);
 492                 return false;
 493             }
 494         }
 495
 496         for (Member m: state.getMembers()) {
 497             if (leaderAddress.equals(m.address())) {
 498                 if (m.status() == MemberStatus.up() || m.status() == MemberStatus.weaklyUp()) {
 499                     log.debug("{}: Leader {} cluster status is {} - leader is available", logName(),
 500                             leaderAddress, m.status());
 501                     return true;
 502                 } else {
 503                     log.debug("{}: Leader {} cluster status is {} - leader is unavailable", logName(),
 504                             leaderAddress, m.status());
 505                     return false;
 506                 }
 507             }
 508         }
 509
 510         log.debug("{}: Leader {} not found in the cluster member set", logName(), leaderAddress);
 511
 512         return false;
 513     }
 514
 515     private void handleInstallSnapshot(final ActorRef sender, InstallSnapshot installSnapshot) {
 516
 517         log.debug("{}: handleInstallSnapshot: {}", logName(), installSnapshot);
 518
 519         leaderId = installSnapshot.getLeaderId();
 520
 521         if (snapshotTracker == null) {
 522             snapshotTracker = new SnapshotTracker(log, installSnapshot.getTotalChunks(), installSnapshot.getLeaderId());
 523         }
 524
 525         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 526
 527         try {
 528             final InstallSnapshotReply reply = new InstallSnapshotReply(
 529                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 530
 531             if (snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 532                     installSnapshot.getLastChunkHashCode())) {
 533                 ByteSource snapshotBytes = ByteSource.wrap(snapshotTracker.getSnapshot());
 534                 Snapshot snapshot = Snapshot.create(
 535                         context.getSnapshotManager().convertSnapshot(snapshotBytes),
 536                         new ArrayList<>(),
 537                         installSnapshot.getLastIncludedIndex(),
 538                         installSnapshot.getLastIncludedTerm(),
 539                         installSnapshot.getLastIncludedIndex(),
 540                         installSnapshot.getLastIncludedTerm(),
 541                         context.getTermInformation().getCurrentTerm(),
 542                         context.getTermInformation().getVotedFor(),
 543                         installSnapshot.getServerConfig().orNull());
 544
 545                 ApplySnapshot.Callback applySnapshotCallback = new ApplySnapshot.Callback() {
 546                     @Override
 547                     public void onSuccess() {
 548                         log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 549
 550                         sender.tell(reply, actor());
 551                     }
 552
 553                     @Override
 554                     public void onFailure() {
 555                         sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(), -1, false), actor());
 556                     }
 557                 };
 558
 559                 actor().tell(new ApplySnapshot(snapshot, applySnapshotCallback), actor());
 560
 561                 snapshotTracker = null;
 562             } else {
 563                 log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 564
 565                 sender.tell(reply, actor());
 566             }
 567         } catch (SnapshotTracker.InvalidChunkException | IOException e) {
 568             log.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 569
 570             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 571                     -1, false), actor());
 572             snapshotTracker = null;
 573
 574         }
 575     }
 576
 577     @Override
 578     public void close() {
 579         stopElection();
 580     }
 581
 582     @VisibleForTesting
 583     SnapshotTracker getSnapshotTracker() {
 584         return snapshotTracker;
 585     }
 586 }