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