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