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

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8
   9 package org.opendaylight.controller.cluster.raft.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.actor.Address;
  14 import akka.cluster.Cluster;
  15 import akka.cluster.ClusterEvent.CurrentClusterState;
  16 import akka.cluster.Member;
  17 import akka.cluster.MemberStatus;
  18 import akka.japi.Procedure;
  19 import com.google.common.annotations.VisibleForTesting;
  20 import com.google.common.base.Stopwatch;
  21 import java.io.IOException;
  22 import java.util.ArrayList;
  23 import java.util.List;
  24 import java.util.Optional;
  25 import java.util.Set;
  26 import java.util.concurrent.TimeUnit;
  27 import java.util.concurrent.atomic.AtomicBoolean;
  28 import javax.annotation.Nullable;
  29 import org.opendaylight.controller.cluster.messaging.MessageAssembler;
  30 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  31 import org.opendaylight.controller.cluster.raft.RaftState;
  32 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  33 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  34 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  35 import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
  36 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  37 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  38 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  39 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  40 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  41 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  42 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  43 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  44 import org.opendaylight.controller.cluster.raft.persisted.Snapshot;
  45
  46 /**
  47  * The behavior of a RaftActor in the Follower raft state.
  48  * <ul>
  49  * <li> Respond to RPCs from candidates and leaders
  50  * <li> If election timeout elapses without receiving AppendEntries
  51  * RPC from current leader or granting vote to candidate:
  52  * convert to candidate
  53  * </ul>
  54  */
  55 public class Follower extends AbstractRaftActorBehavior {
  56     private static final long MAX_ELECTION_TIMEOUT_FACTOR = 18;
  57
  58     private final SyncStatusTracker initialSyncStatusTracker;
  59
  60     private final MessageAssembler appendEntriesMessageAssembler;
  61
  62     private final Stopwatch lastLeaderMessageTimer = Stopwatch.createStarted();
  63     private SnapshotTracker snapshotTracker = null;
  64     private String leaderId;
  65     private short leaderPayloadVersion;
  66
  67     public Follower(final RaftActorContext context) {
  68         this(context, null, (short)-1);
  69     }
  70
  71     public Follower(final RaftActorContext context, final String initialLeaderId,
  72             final short initialLeaderPayloadVersion) {
  73         super(context, RaftState.Follower);
  74         this.leaderId = initialLeaderId;
  75         this.leaderPayloadVersion = initialLeaderPayloadVersion;
  76
  77         initialSyncStatusTracker = new SyncStatusTracker(context.getActor(), getId(), context.getConfigParams()
  78             .getSyncIndexThreshold());
  79
  80         appendEntriesMessageAssembler = MessageAssembler.builder().logContext(logName())
  81                 .fileBackedStreamFactory(context.getFileBackedOutputStreamFactory())
  82                 .assembledMessageCallback((message, sender) -> handleMessage(sender, message)).build();
  83
  84         if (context.getPeerIds().isEmpty() && getLeaderId() == null) {
  85             actor().tell(TimeoutNow.INSTANCE, actor());
  86         } else {
  87             scheduleElection(electionDuration());
  88         }
  89     }
  90
  91     @Override
  92     public final String getLeaderId() {
  93         return leaderId;
  94     }
  95
  96     @VisibleForTesting
  97     protected final void setLeaderId(@Nullable final String leaderId) {
  98         this.leaderId = leaderId;
  99     }
 100
 101     @Override
 102     public short getLeaderPayloadVersion() {
 103         return leaderPayloadVersion;
 104     }
 105
 106     @VisibleForTesting
 107     protected final void setLeaderPayloadVersion(final short leaderPayloadVersion) {
 108         this.leaderPayloadVersion = leaderPayloadVersion;
 109     }
 110
 111     private void restartLastLeaderMessageTimer() {
 112         if (lastLeaderMessageTimer.isRunning()) {
 113             lastLeaderMessageTimer.reset();
 114         }
 115
 116         lastLeaderMessageTimer.start();
 117     }
 118
 119     private boolean isLogEntryPresent(final long index) {
 120         if (context.getReplicatedLog().isInSnapshot(index)) {
 121             return true;
 122         }
 123
 124         ReplicatedLogEntry entry = context.getReplicatedLog().get(index);
 125         return entry != null;
 126
 127     }
 128
 129     private void updateInitialSyncStatus(final long currentLeaderCommit, final String newLeaderId) {
 130         initialSyncStatusTracker.update(newLeaderId, currentLeaderCommit, context.getCommitIndex());
 131     }
 132
 133     @Override
 134     protected RaftActorBehavior handleAppendEntries(final ActorRef sender, final AppendEntries appendEntries) {
 135         int numLogEntries = appendEntries.getEntries().size();
 136         if (log.isTraceEnabled()) {
 137             log.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
 138         } else if (log.isDebugEnabled() && numLogEntries > 0) {
 139             log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 140         }
 141
 142         if (snapshotTracker != null && !snapshotTracker.getLeaderId().equals(appendEntries.getLeaderId())) {
 143             log.debug("{}: snapshot install is in progress but the prior snapshot leaderId {} does not match the "
 144                 + "AppendEntries leaderId {}", logName(), snapshotTracker.getLeaderId(), appendEntries.getLeaderId());
 145             closeSnapshotTracker();
 146         }
 147
 148         if (snapshotTracker != null || context.getSnapshotManager().isApplying()) {
 149             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
 150             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 151                     lastIndex(), lastTerm(), context.getPayloadVersion());
 152
 153             log.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
 154             sender.tell(reply, actor());
 155
 156             return this;
 157         }
 158
 159         // If we got here then we do appear to be talking to the leader
 160         leaderId = appendEntries.getLeaderId();
 161         leaderPayloadVersion = appendEntries.getPayloadVersion();
 162
 163         // First check if the logs are in sync or not
 164         if (isOutOfSync(appendEntries, sender)) {
 165             updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 166             return this;
 167         }
 168
 169         if (!processNewEntries(appendEntries, sender)) {
 170             updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 171             return this;
 172         }
 173
 174         long lastIndex = lastIndex();
 175         long prevCommitIndex = context.getCommitIndex();
 176
 177         // If leaderCommit > commitIndex, set commitIndex = min(leaderCommit, index of last new entry)
 178         if (appendEntries.getLeaderCommit() > prevCommitIndex) {
 179             context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 180         }
 181
 182         if (prevCommitIndex != context.getCommitIndex()) {
 183             log.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 184         }
 185
 186         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 187                 lastIndex, lastTerm(), context.getPayloadVersion());
 188
 189         if (log.isTraceEnabled()) {
 190             log.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 191         } else if (log.isDebugEnabled() && numLogEntries > 0) {
 192             log.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 193         }
 194
 195         // Reply to the leader before applying any previous state so as not to hold up leader consensus.
 196         sender.tell(reply, actor());
 197
 198         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 199
 200         // If leaderCommit > lastApplied, increment lastApplied and apply log[lastApplied] to state machine (§5.3).
 201         // lastApplied can be equal to lastIndex.
 202         if (appendEntries.getLeaderCommit() > context.getLastApplied() && context.getLastApplied() < lastIndex) {
 203             if (log.isDebugEnabled()) {
 204                 log.debug("{}: applyLogToStateMachine, appendEntries.getLeaderCommit(): {}, "
 205                         + "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 206                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 207             }
 208
 209             applyLogToStateMachine(appendEntries.getLeaderCommit());
 210         }
 211
 212         if (!context.getSnapshotManager().isCapturing()) {
 213             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 214         }
 215
 216         appendEntriesMessageAssembler.checkExpiredAssembledMessageState();
 217
 218         return this;
 219     }
 220
 221     private boolean processNewEntries(final AppendEntries appendEntries, final ActorRef sender) {
 222         int numLogEntries = appendEntries.getEntries().size();
 223         if (numLogEntries == 0) {
 224             return true;
 225         }
 226
 227         log.debug("{}: Number of entries to be appended = {}", logName(), numLogEntries);
 228
 229         long lastIndex = lastIndex();
 230         int addEntriesFrom = 0;
 231
 232         // First check for conflicting entries. If an existing entry conflicts with a new one (same index but different
 233         // term), delete the existing entry and all that follow it (§5.3)
 234         if (context.getReplicatedLog().size() > 0) {
 235             // Find the entry up until the one that is not in the follower's log
 236             for (int i = 0;i < numLogEntries; i++, addEntriesFrom++) {
 237                 ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 238
 239                 if (!isLogEntryPresent(matchEntry.getIndex())) {
 240                     // newEntry not found in the log
 241                     break;
 242                 }
 243
 244                 long existingEntryTerm = getLogEntryTerm(matchEntry.getIndex());
 245
 246                 log.debug("{}: matchEntry {} is present: existingEntryTerm: {}", logName(), matchEntry,
 247                         existingEntryTerm);
 248
 249                 // existingEntryTerm == -1 means it's in the snapshot and not in the log. We don't know
 250                 // what the term was so we'll assume it matches.
 251                 if (existingEntryTerm == -1 || existingEntryTerm == matchEntry.getTerm()) {
 252                     continue;
 253                 }
 254
 255                 if (!context.getRaftPolicy().applyModificationToStateBeforeConsensus()) {
 256                     log.info("{}: Removing entries from log starting at {}", logName(), matchEntry.getIndex());
 257
 258                     // Entries do not match so remove all subsequent entries
 259                     if (!context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex())) {
 260                         // Could not remove the entries - this means the matchEntry index must be in the
 261                         // snapshot and not the log. In this case the prior entries are part of the state
 262                         // so we must send back a reply to force a snapshot to completely re-sync the
 263                         // follower's log and state.
 264
 265                         log.info("{}: Could not remove entries - sending reply to force snapshot", logName());
 266                         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 267                                 lastTerm(), context.getPayloadVersion(), true), actor());
 268                         return false;
 269                     }
 270
 271                     break;
 272                 } else {
 273                     sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 274                             lastTerm(), context.getPayloadVersion(), true), actor());
 275                     return false;
 276                 }
 277             }
 278         }
 279
 280         lastIndex = lastIndex();
 281         log.debug("{}: After cleanup, lastIndex: {}, entries to be added from: {}", logName(), lastIndex,
 282                 addEntriesFrom);
 283
 284         // When persistence successfully completes for each new log entry appended, we need to determine if we
 285         // should capture a snapshot to compact the persisted log. shouldCaptureSnapshot tracks whether or not
 286         // one of the log entries has exceeded the log size threshold whereby a snapshot should be taken. However
 287         // we don't initiate the snapshot at that log entry but rather after the last log entry has been persisted.
 288         // This is done because subsequent log entries after the one that tripped the threshold may have been
 289         // applied to the state already, as the persistence callback occurs async, and we want those entries
 290         // purged from the persisted log as well.
 291         final AtomicBoolean shouldCaptureSnapshot = new AtomicBoolean(false);
 292         final Procedure<ReplicatedLogEntry> appendAndPersistCallback = logEntry -> {
 293             final List<ReplicatedLogEntry> entries = appendEntries.getEntries();
 294             final ReplicatedLogEntry lastEntryToAppend = entries.get(entries.size() - 1);
 295             if (shouldCaptureSnapshot.get() && logEntry == lastEntryToAppend) {
 296                 context.getSnapshotManager().capture(context.getReplicatedLog().last(), getReplicatedToAllIndex());
 297             }
 298         };
 299
 300         // Append any new entries not already in the log
 301         for (int i = addEntriesFrom; i < numLogEntries; i++) {
 302             ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 303
 304             log.debug("{}: Append entry to log {}", logName(), entry.getData());
 305
 306             context.getReplicatedLog().appendAndPersist(entry, appendAndPersistCallback, false);
 307
 308             shouldCaptureSnapshot.compareAndSet(false,
 309                     context.getReplicatedLog().shouldCaptureSnapshot(entry.getIndex()));
 310
 311             if (entry.getData() instanceof ServerConfigurationPayload) {
 312                 context.updatePeerIds((ServerConfigurationPayload)entry.getData());
 313             }
 314         }
 315
 316         log.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 317
 318         return true;
 319     }
 320
 321     private boolean isOutOfSync(final AppendEntries appendEntries, final ActorRef sender) {
 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
 332             sendOutOfSyncAppendEntriesReply(sender, false);
 333             return true;
 334         }
 335
 336         if (lastIndex > -1) {
 337             if (isLogEntryPresent(appendEntries.getPrevLogIndex())) {
 338                 final long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 339                 if (prevLogTerm != appendEntries.getPrevLogTerm()) {
 340
 341                     // The follower's log is out of sync because the Leader's prevLogIndex entry does exist
 342                     // in the follower's log but it has a different term in it
 343
 344                     log.info("{}: The prevLogIndex {} was found in the log but the term {} is not equal to the append "
 345                             + "entries prevLogTerm {} - lastIndex: {}, snapshotIndex: {}", logName(),
 346                             appendEntries.getPrevLogIndex(), prevLogTerm, appendEntries.getPrevLogTerm(), lastIndex,
 347                             context.getReplicatedLog().getSnapshotIndex());
 348
 349                     sendOutOfSyncAppendEntriesReply(sender, false);
 350                     return true;
 351                 }
 352             } else if (appendEntries.getPrevLogIndex() != -1) {
 353
 354                 // The follower's log is out of sync because the Leader's prevLogIndex entry was not found in it's log
 355
 356                 log.info("{}: The log is not empty but the prevLogIndex {} was not found in it - lastIndex: {}, "
 357                         + "snapshotIndex: {}", logName(), appendEntries.getPrevLogIndex(), lastIndex,
 358                         context.getReplicatedLog().getSnapshotIndex());
 359
 360                 sendOutOfSyncAppendEntriesReply(sender, false);
 361                 return true;
 362             }
 363         }
 364
 365         if (appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 366                 && appendEntries.getReplicatedToAllIndex() != -1) {
 367             if (!isLogEntryPresent(appendEntries.getReplicatedToAllIndex())) {
 368                 // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
 369                 // the previous entry in it's in-memory journal
 370
 371                 log.info("{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the "
 372                         + "in-memory journal", logName(), appendEntries.getReplicatedToAllIndex());
 373
 374                 sendOutOfSyncAppendEntriesReply(sender, false);
 375                 return true;
 376             }
 377
 378             final List<ReplicatedLogEntry> entries = appendEntries.getEntries();
 379             if (entries.size() > 0 && !isLogEntryPresent(entries.get(0).getIndex() - 1)) {
 380                 log.info("{}: Cannot append entries because the calculated previousIndex {} was not found in the "
 381                         + "in-memory journal", logName(), entries.get(0).getIndex() - 1);
 382
 383                 sendOutOfSyncAppendEntriesReply(sender, false);
 384                 return true;
 385             }
 386         }
 387
 388         return false;
 389     }
 390
 391     private void sendOutOfSyncAppendEntriesReply(final ActorRef sender, boolean forceInstallSnapshot) {
 392         // We found that the log was out of sync so just send a negative reply.
 393         final AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex(),
 394                 lastTerm(), context.getPayloadVersion(), forceInstallSnapshot);
 395
 396         log.info("{}: Follower is out-of-sync so sending negative reply: {}", logName(), reply);
 397         sender.tell(reply, actor());
 398     }
 399
 400     @Override
 401     protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
 402         final AppendEntriesReply appendEntriesReply) {
 403         return this;
 404     }
 405
 406     @Override
 407     protected RaftActorBehavior handleRequestVoteReply(final ActorRef sender,
 408         final RequestVoteReply requestVoteReply) {
 409         return this;
 410     }
 411
 412     @Override
 413     public RaftActorBehavior handleMessage(final ActorRef sender, final Object message) {
 414         if (message instanceof ElectionTimeout || message instanceof TimeoutNow) {
 415             return handleElectionTimeout(message);
 416         }
 417
 418         if (appendEntriesMessageAssembler.handleMessage(message, actor())) {
 419             return this;
 420         }
 421
 422         if (!(message instanceof RaftRPC)) {
 423             // The rest of the processing requires the message to be a RaftRPC
 424             return null;
 425         }
 426
 427         final RaftRPC rpc = (RaftRPC) message;
 428         // If RPC request or response contains term T > currentTerm:
 429         // set currentTerm = T, convert to follower (§5.1)
 430         // This applies to all RPC messages and responses
 431         if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 432             log.info("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 433                 logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 434
 435             context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 436         }
 437
 438         if (rpc instanceof InstallSnapshot) {
 439             handleInstallSnapshot(sender, (InstallSnapshot) rpc);
 440             restartLastLeaderMessageTimer();
 441             scheduleElection(electionDuration());
 442             return this;
 443         }
 444
 445         if (!(rpc instanceof RequestVote) || canGrantVote((RequestVote) rpc)) {
 446             restartLastLeaderMessageTimer();
 447             scheduleElection(electionDuration());
 448         }
 449
 450         return super.handleMessage(sender, rpc);
 451     }
 452
 453     private RaftActorBehavior handleElectionTimeout(final Object message) {
 454         // If the message is ElectionTimeout, verify we haven't actually seen a message from the leader
 455         // during the election timeout interval. It may that the election timer expired b/c this actor
 456         // was busy and messages got delayed, in which case leader messages would be backed up in the
 457         // queue but would be processed before the ElectionTimeout message and thus would restart the
 458         // lastLeaderMessageTimer.
 459         long lastLeaderMessageInterval = lastLeaderMessageTimer.elapsed(TimeUnit.MILLISECONDS);
 460         long electionTimeoutInMillis = context.getConfigParams().getElectionTimeOutInterval().toMillis();
 461         boolean noLeaderMessageReceived = !lastLeaderMessageTimer.isRunning()
 462                 || lastLeaderMessageInterval >= electionTimeoutInMillis;
 463
 464         if (canStartElection()) {
 465             if (message instanceof TimeoutNow) {
 466                 log.debug("{}: Received TimeoutNow - switching to Candidate", logName());
 467                 return internalSwitchBehavior(RaftState.Candidate);
 468             } else if (noLeaderMessageReceived) {
 469                 // Check the cluster state to see if the leader is known to be up before we go to Candidate.
 470                 // However if we haven't heard from the leader in a long time even though the cluster state
 471                 // indicates it's up then something is wrong - leader might be stuck indefinitely - so switch
 472                 // to Candidate,
 473                 long maxElectionTimeout = electionTimeoutInMillis * MAX_ELECTION_TIMEOUT_FACTOR;
 474                 if (isLeaderAvailabilityKnown() && lastLeaderMessageInterval < maxElectionTimeout) {
 475                     log.debug("{}: Received ElectionTimeout but leader appears to be available", logName());
 476                     scheduleElection(electionDuration());
 477                 } else {
 478                     log.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 479                     return internalSwitchBehavior(RaftState.Candidate);
 480                 }
 481             } else {
 482                 log.debug("{}: Received ElectionTimeout but lastLeaderMessageInterval {} < election timeout {}",
 483                         logName(), lastLeaderMessageInterval, context.getConfigParams().getElectionTimeOutInterval());
 484                 scheduleElection(electionDuration());
 485             }
 486         } else if (message instanceof ElectionTimeout) {
 487             if (noLeaderMessageReceived) {
 488                 setLeaderId(null);
 489             }
 490
 491             scheduleElection(electionDuration());
 492         }
 493
 494         return this;
 495     }
 496
 497     private boolean isLeaderAvailabilityKnown() {
 498         if (leaderId == null) {
 499             return false;
 500         }
 501
 502         Optional<Cluster> cluster = context.getCluster();
 503         if (!cluster.isPresent()) {
 504             return false;
 505         }
 506
 507         ActorSelection leaderActor = context.getPeerActorSelection(leaderId);
 508         if (leaderActor == null) {
 509             return false;
 510         }
 511
 512         Address leaderAddress = leaderActor.anchorPath().address();
 513
 514         CurrentClusterState state = cluster.get().state();
 515         Set<Member> unreachable = state.getUnreachable();
 516
 517         log.debug("{}: Checking for leader {} in the cluster unreachable set {}", logName(), leaderAddress,
 518                 unreachable);
 519
 520         for (Member m: unreachable) {
 521             if (leaderAddress.equals(m.address())) {
 522                 log.info("{}: Leader {} is unreachable", logName(), leaderAddress);
 523                 return false;
 524             }
 525         }
 526
 527         for (Member m: state.getMembers()) {
 528             if (leaderAddress.equals(m.address())) {
 529                 if (m.status() == MemberStatus.up() || m.status() == MemberStatus.weaklyUp()) {
 530                     log.debug("{}: Leader {} cluster status is {} - leader is available", logName(),
 531                             leaderAddress, m.status());
 532                     return true;
 533                 } else {
 534                     log.debug("{}: Leader {} cluster status is {} - leader is unavailable", logName(),
 535                             leaderAddress, m.status());
 536                     return false;
 537                 }
 538             }
 539         }
 540
 541         log.debug("{}: Leader {} not found in the cluster member set", logName(), leaderAddress);
 542
 543         return false;
 544     }
 545
 546     private void handleInstallSnapshot(final ActorRef sender, final InstallSnapshot installSnapshot) {
 547
 548         log.debug("{}: handleInstallSnapshot: {}", logName(), installSnapshot);
 549
 550         leaderId = installSnapshot.getLeaderId();
 551
 552         if (snapshotTracker == null) {
 553             snapshotTracker = new SnapshotTracker(log, installSnapshot.getTotalChunks(), installSnapshot.getLeaderId(),
 554                     context);
 555         }
 556
 557         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 558
 559         try {
 560             final InstallSnapshotReply reply = new InstallSnapshotReply(
 561                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 562
 563             if (snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 564                     installSnapshot.getLastChunkHashCode())) {
 565
 566                 log.info("{}: Snapshot installed from leader: {}", logName(), installSnapshot.getLeaderId());
 567
 568                 Snapshot snapshot = Snapshot.create(
 569                         context.getSnapshotManager().convertSnapshot(snapshotTracker.getSnapshotBytes()),
 570                         new ArrayList<>(),
 571                         installSnapshot.getLastIncludedIndex(),
 572                         installSnapshot.getLastIncludedTerm(),
 573                         installSnapshot.getLastIncludedIndex(),
 574                         installSnapshot.getLastIncludedTerm(),
 575                         context.getTermInformation().getCurrentTerm(),
 576                         context.getTermInformation().getVotedFor(),
 577                         installSnapshot.getServerConfig().orNull());
 578
 579                 ApplySnapshot.Callback applySnapshotCallback = new ApplySnapshot.Callback() {
 580                     @Override
 581                     public void onSuccess() {
 582                         log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 583
 584                         sender.tell(reply, actor());
 585                     }
 586
 587                     @Override
 588                     public void onFailure() {
 589                         sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(), -1, false), actor());
 590                     }
 591                 };
 592
 593                 actor().tell(new ApplySnapshot(snapshot, applySnapshotCallback), actor());
 594
 595                 closeSnapshotTracker();
 596             } else {
 597                 log.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 598
 599                 sender.tell(reply, actor());
 600             }
 601         } catch (IOException e) {
 602             log.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 603
 604             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 605                     -1, false), actor());
 606
 607             closeSnapshotTracker();
 608         }
 609     }
 610
 611     private void closeSnapshotTracker() {
 612         if (snapshotTracker != null) {
 613             snapshotTracker.close();
 614             snapshotTracker = null;
 615         }
 616     }
 617
 618     @Override
 619     public void close() {
 620         closeSnapshotTracker();
 621         stopElection();
 622         appendEntriesMessageAssembler.close();
 623     }
 624
 625     @VisibleForTesting
 626     SnapshotTracker getSnapshotTracker() {
 627         return snapshotTracker;
 628     }
 629 }