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.japi.Procedure;
  13 import com.google.common.annotations.VisibleForTesting;
  14 import java.util.ArrayList;
  15 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  16 import org.opendaylight.controller.cluster.raft.RaftState;
  17 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  18 import org.opendaylight.controller.cluster.raft.ServerConfigurationPayload;
  19 import org.opendaylight.controller.cluster.raft.Snapshot;
  20 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  21 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  22 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  23 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  24 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  25 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  26 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  27 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  28 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  29
  30 /**
  31  * The behavior of a RaftActor in the Follower state
  32  * <p/>
  33  * <ul>
  34  * <li> Respond to RPCs from candidates and leaders
  35  * <li> If election timeout elapses without receiving AppendEntries
  36  * RPC from current leader or granting vote to candidate:
  37  * convert to candidate
  38  * </ul>
  39  */
  40 public class Follower extends AbstractRaftActorBehavior {
  41     private static final int SYNC_THRESHOLD = 10;
  42
  43     private final SyncStatusTracker initialSyncStatusTracker;
  44
  45     private final Procedure<ReplicatedLogEntry> appendAndPersistCallback = new Procedure<ReplicatedLogEntry>() {
  46         @Override
  47         public void apply(ReplicatedLogEntry logEntry) {
  48             context.getReplicatedLog().captureSnapshotIfReady(logEntry);
  49         }
  50     };
  51
  52     private SnapshotTracker snapshotTracker = null;
  53
  54     public Follower(RaftActorContext context) {
  55         this(context, null, (short)-1);
  56     }
  57
  58     public Follower(RaftActorContext context, String initialLeaderId, short initialLeaderPayloadVersion) {
  59         super(context, RaftState.Follower);
  60         leaderId = initialLeaderId;
  61         setLeaderPayloadVersion(initialLeaderPayloadVersion);
  62
  63         initialSyncStatusTracker = new SyncStatusTracker(context.getActor(), getId(), SYNC_THRESHOLD);
  64
  65         if(canStartElection()) {
  66             if (context.getPeerIds().isEmpty() && getLeaderId() == null) {
  67                 actor().tell(ElectionTimeout.INSTANCE, actor());
  68             } else {
  69                 scheduleElection(electionDuration());
  70             }
  71         }
  72
  73     }
  74
  75     private boolean isLogEntryPresent(long index){
  76         if(index == context.getReplicatedLog().getSnapshotIndex()){
  77             return true;
  78         }
  79
  80         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  81                 .get(index);
  82
  83         return previousEntry != null;
  84
  85     }
  86
  87     private long getLogEntryTerm(long index){
  88         if(index == context.getReplicatedLog().getSnapshotIndex()){
  89             return context.getReplicatedLog().getSnapshotTerm();
  90         }
  91
  92         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  93                 .get(index);
  94
  95         if(previousEntry != null){
  96             return previousEntry.getTerm();
  97         }
  98
  99         return -1;
 100     }
 101
 102     private void updateInitialSyncStatus(long currentLeaderCommit, String leaderId){
 103         initialSyncStatusTracker.update(leaderId, currentLeaderCommit, context.getCommitIndex());
 104     }
 105
 106     @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 107                                                               AppendEntries appendEntries) {
 108
 109         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
 110         if(LOG.isTraceEnabled()) {
 111             LOG.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
 112         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
 113             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 114         }
 115
 116         // TODO : Refactor this method into a bunch of smaller methods
 117         // to make it easier to read. Before refactoring ensure tests
 118         // cover the code properly
 119
 120         if (snapshotTracker != null || context.getSnapshotManager().isApplying()) {
 121             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
 122             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 123                     lastIndex(), lastTerm(), context.getPayloadVersion());
 124
 125             if(LOG.isDebugEnabled()) {
 126                 LOG.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
 127             }
 128             sender.tell(reply, actor());
 129
 130             return this;
 131         }
 132
 133         // If we got here then we do appear to be talking to the leader
 134         leaderId = appendEntries.getLeaderId();
 135
 136         setLeaderPayloadVersion(appendEntries.getPayloadVersion());
 137
 138         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 139         // First check if the logs are in sync or not
 140         long lastIndex = lastIndex();
 141
 142         if (isOutOfSync(appendEntries)) {
 143             // We found that the log was out of sync so just send a negative
 144             // reply and return
 145
 146             LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
 147                         logName(), lastIndex, lastTerm());
 148
 149             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 150                     lastTerm(), context.getPayloadVersion()), actor());
 151             return this;
 152         }
 153
 154         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
 155
 156             LOG.debug("{}: Number of entries to be appended = {}", logName(),
 157                         appendEntries.getEntries().size());
 158
 159             // 3. If an existing entry conflicts with a new one (same index
 160             // but different terms), delete the existing entry and all that
 161             // follow it (§5.3)
 162             int addEntriesFrom = 0;
 163             if (context.getReplicatedLog().size() > 0) {
 164
 165                 // Find the entry up until the one that is not in the follower's log
 166                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 167                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 168                     ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
 169
 170                     if (newEntry == null) {
 171                         //newEntry not found in the log
 172                         break;
 173                     }
 174
 175                     if (newEntry.getTerm() == matchEntry.getTerm()) {
 176                         continue;
 177                     }
 178
 179                     if(!context.getRaftPolicy().applyModificationToStateBeforeConsensus()) {
 180
 181                         LOG.debug("{}: Removing entries from log starting at {}", logName(),
 182                                 matchEntry.getIndex());
 183
 184                         // Entries do not match so remove all subsequent entries
 185                         context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex());
 186                         break;
 187                     } else {
 188                         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 189                                 lastTerm(), context.getPayloadVersion(), true), actor());
 190                         return this;
 191                     }
 192                 }
 193             }
 194
 195             lastIndex = lastIndex();
 196             LOG.debug("{}: After cleanup entries to be added from = {}", logName(),
 197                         (addEntriesFrom + lastIndex));
 198
 199             // 4. Append any new entries not already in the log
 200             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
 201                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 202
 203                 LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
 204
 205                 context.getReplicatedLog().appendAndPersist(entry, appendAndPersistCallback);
 206
 207                 if(entry.getData() instanceof ServerConfigurationPayload) {
 208                     context.updatePeerIds((ServerConfigurationPayload)entry.getData());
 209                 }
 210             }
 211
 212             LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 213         }
 214
 215         // 5. If leaderCommit > commitIndex, set commitIndex =
 216         // min(leaderCommit, index of last new entry)
 217
 218         lastIndex = lastIndex();
 219         long prevCommitIndex = context.getCommitIndex();
 220
 221         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 222
 223         if (prevCommitIndex != context.getCommitIndex()) {
 224             LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 225         }
 226
 227         // If commitIndex > lastApplied: increment lastApplied, apply
 228         // log[lastApplied] to state machine (§5.3)
 229         // check if there are any entries to be applied. last-applied can be equal to last-index
 230         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
 231             context.getLastApplied() < lastIndex) {
 232             if(LOG.isDebugEnabled()) {
 233                 LOG.debug("{}: applyLogToStateMachine, " +
 234                         "appendEntries.getLeaderCommit(): {}," +
 235                         "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 236                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 237             }
 238
 239             applyLogToStateMachine(appendEntries.getLeaderCommit());
 240         }
 241
 242         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 243             lastIndex, lastTerm(), context.getPayloadVersion());
 244
 245         if(LOG.isTraceEnabled()) {
 246             LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 247         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
 248             LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 249         }
 250
 251         sender.tell(reply, actor());
 252
 253         if (!context.getSnapshotManager().isCapturing()) {
 254             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 255         }
 256
 257         return this;
 258     }
 259
 260     private boolean isOutOfSync(AppendEntries appendEntries) {
 261
 262         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 263         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
 264         long lastIndex = lastIndex();
 265         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
 266         boolean outOfSync = true;
 267
 268         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 269
 270             // The follower's log is out of sync because the leader does have
 271             // an entry at prevLogIndex and this follower has no entries in
 272             // it's log.
 273
 274             LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
 275                         logName(), appendEntries.getPrevLogIndex());
 276         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
 277
 278             // The follower's log is out of sync because the Leader's
 279             // prevLogIndex entry was not found in it's log
 280
 281             LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it",
 282                         logName(), appendEntries.getPrevLogIndex());
 283         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
 284
 285             // The follower's log is out of sync because the Leader's
 286             // prevLogIndex entry does exist in the follower's log but it has
 287             // a different term in it
 288
 289             LOG.debug(
 290                     "{}: Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}",
 291                     logName(), prevLogTerm, appendEntries.getPrevLogTerm());
 292         } else if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 293                 && appendEntries.getReplicatedToAllIndex() != -1
 294                 && !isLogEntryPresent(appendEntries.getReplicatedToAllIndex())
 295                 && !context.getReplicatedLog().isInSnapshot(appendEntries.getReplicatedToAllIndex())) {
 296             // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
 297             // the previous entry in it's in-memory journal
 298
 299             LOG.debug(
 300                     "{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the in-memory journal",
 301                     logName(), appendEntries.getReplicatedToAllIndex());
 302         } else if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
 303                 && appendEntries.getReplicatedToAllIndex() != -1 && numLogEntries > 0
 304                 && !isLogEntryPresent(appendEntries.getEntries().get(0).getIndex() - 1)
 305                 && !context.getReplicatedLog().isInSnapshot(appendEntries.getEntries().get(0).getIndex() - 1)) {
 306             LOG.debug(
 307                     "{}: Cannot append entries because the calculated previousIndex {} was not found in the in-memory journal",
 308                     logName(), appendEntries.getEntries().get(0).getIndex() - 1);
 309         } else {
 310             outOfSync = false;
 311         }
 312         return outOfSync;
 313     }
 314
 315     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 316         AppendEntriesReply appendEntriesReply) {
 317         return this;
 318     }
 319
 320     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 321         RequestVoteReply requestVoteReply) {
 322         return this;
 323     }
 324
 325     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 326
 327         Object message = fromSerializableMessage(originalMessage);
 328
 329         if (message instanceof RaftRPC) {
 330             RaftRPC rpc = (RaftRPC) message;
 331             // If RPC request or response contains term T > currentTerm:
 332             // set currentTerm = T, convert to follower (§5.1)
 333             // This applies to all RPC messages and responses
 334             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 335                 LOG.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 336                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 337
 338                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 339             }
 340         }
 341
 342         if (message instanceof ElectionTimeout) {
 343             if(canStartElection()) {
 344                 LOG.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 345                 return internalSwitchBehavior(RaftState.Candidate);
 346             } else {
 347                 return this;
 348             }
 349
 350         } else if (message instanceof InstallSnapshot) {
 351             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 352             handleInstallSnapshot(sender, installSnapshot);
 353         }
 354
 355         if(message instanceof RaftRPC && (!(message instanceof RequestVote) || (canGrantVote((RequestVote) message)))){
 356             scheduleElection(electionDuration());
 357         }
 358
 359         return super.handleMessage(sender, message);
 360     }
 361
 362     private void handleInstallSnapshot(final ActorRef sender, InstallSnapshot installSnapshot) {
 363
 364         LOG.debug("{}: handleInstallSnapshot: {}", logName(), installSnapshot);
 365
 366         leaderId = installSnapshot.getLeaderId();
 367
 368         if(snapshotTracker == null){
 369             snapshotTracker = new SnapshotTracker(LOG, installSnapshot.getTotalChunks());
 370         }
 371
 372         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 373
 374         try {
 375             final InstallSnapshotReply reply = new InstallSnapshotReply(
 376                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 377
 378             if(snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 379                     installSnapshot.getLastChunkHashCode())){
 380                 Snapshot snapshot = Snapshot.create(snapshotTracker.getSnapshot(),
 381                         new ArrayList<ReplicatedLogEntry>(),
 382                         installSnapshot.getLastIncludedIndex(),
 383                         installSnapshot.getLastIncludedTerm(),
 384                         installSnapshot.getLastIncludedIndex(),
 385                         installSnapshot.getLastIncludedTerm(),
 386                         context.getTermInformation().getCurrentTerm(),
 387                         context.getTermInformation().getVotedFor(),
 388                         context.getPeerServerInfo(true));
 389
 390                 ApplySnapshot.Callback applySnapshotCallback = new ApplySnapshot.Callback() {
 391                     @Override
 392                     public void onSuccess() {
 393                         LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 394
 395                         sender.tell(reply, actor());
 396                     }
 397
 398                     @Override
 399                     public void onFailure() {
 400                         sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(), -1, false), actor());
 401                     }
 402                 };
 403
 404                 actor().tell(new ApplySnapshot(snapshot, applySnapshotCallback), actor());
 405
 406                 snapshotTracker = null;
 407             } else {
 408                 LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 409
 410                 sender.tell(reply, actor());
 411             }
 412         } catch (SnapshotTracker.InvalidChunkException e) {
 413             LOG.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 414
 415             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 416                     -1, false), actor());
 417             snapshotTracker = null;
 418
 419         } catch (Exception e){
 420             LOG.error("{}: Exception in InstallSnapshot of follower", logName(), e);
 421
 422             //send reply with success as false. The chunk will be sent again on failure
 423             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 424                     installSnapshot.getChunkIndex(), false), actor());
 425
 426         }
 427     }
 428
 429     @Override
 430     public void close() throws Exception {
 431         stopElection();
 432     }
 433
 434     @VisibleForTesting
 435     SnapshotTracker getSnapshotTracker(){
 436         return snapshotTracker;
 437     }
 438 }