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 org.opendaylight.controller.cluster.raft.RaftActorContext;
  13 import org.opendaylight.controller.cluster.raft.RaftState;
  14 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  15 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  16 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  17 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  18 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  19 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  20 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  21 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  22
  23 /**
  24  * The behavior of a RaftActor in the Follower state
  25  * <p/>
  26  * <ul>
  27  * <li> Respond to RPCs from candidates and leaders
  28  * <li> If election timeout elapses without receiving AppendEntries
  29  * RPC from current leader or granting vote to candidate:
  30  * convert to candidate
  31  * </ul>
  32  */
  33 public class Follower extends AbstractRaftActorBehavior {
  34     public Follower(RaftActorContext context) {
  35         super(context);
  36
  37         scheduleElection(electionDuration());
  38     }
  39
  40     @Override protected RaftState handleAppendEntries(ActorRef sender,
  41         AppendEntries appendEntries) {
  42
  43         if(appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
  44             context.getLogger()
  45                 .info("Follower: Received {}", appendEntries.toString());
  46         }
  47
  48         // TODO : Refactor this method into a bunch of smaller methods
  49         // to make it easier to read. Before refactoring ensure tests
  50         // cover the code properly
  51
  52         // 1. Reply false if term < currentTerm (§5.1)
  53         // This is handled in the appendEntries method of the base class
  54
  55         // If we got here then we do appear to be talking to the leader
  56         leaderId = appendEntries.getLeaderId();
  57
  58         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
  59         // whose term matches prevLogTerm (§5.3)
  60
  61         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  62             .get(appendEntries.getPrevLogIndex());
  63
  64
  65         boolean outOfSync = true;
  66
  67         // First check if the logs are in sync or not
  68         if (lastIndex() == -1
  69             && appendEntries.getPrevLogIndex() != -1) {
  70
  71             // The follower's log is out of sync because the leader does have
  72             // an entry at prevLogIndex and this follower has no entries in
  73             // it's log.
  74
  75             context.getLogger().debug(
  76                 "The followers log is empty and the senders prevLogIndex is {}",
  77                 appendEntries.getPrevLogIndex());
  78
  79         } else if (lastIndex() > -1
  80             && appendEntries.getPrevLogIndex() != -1
  81             && previousEntry == null) {
  82
  83             // The follower's log is out of sync because the Leader's
  84             // prevLogIndex entry was not found in it's log
  85
  86             context.getLogger().debug(
  87                 "The log is not empty but the prevLogIndex {} was not found in it",
  88                 appendEntries.getPrevLogIndex());
  89
  90         } else if (lastIndex() > -1
  91             && previousEntry != null
  92             && previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
  93
  94             // The follower's log is out of sync because the Leader's
  95             // prevLogIndex entry does exist in the follower's log but it has
  96             // a different term in it
  97
  98             context.getLogger().debug(
  99                 "Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}"
 100                 , previousEntry.getTerm()
 101                 , appendEntries.getPrevLogTerm());
 102         } else {
 103             outOfSync = false;
 104         }
 105
 106         if (outOfSync) {
 107             // We found that the log was out of sync so just send a negative
 108             // reply and return
 109             sender.tell(
 110                 new AppendEntriesReply(context.getId(), currentTerm(), false,
 111                     lastIndex(), lastTerm()), actor()
 112             );
 113             return state();
 114         }
 115
 116         if (appendEntries.getEntries() != null
 117             && appendEntries.getEntries().size() > 0) {
 118             context.getLogger().debug(
 119                 "Number of entries to be appended = " + appendEntries
 120                     .getEntries().size()
 121             );
 122
 123             // 3. If an existing entry conflicts with a new one (same index
 124             // but different terms), delete the existing entry and all that
 125             // follow it (§5.3)
 126             int addEntriesFrom = 0;
 127             if (context.getReplicatedLog().size() > 0) {
 128
 129                 // Find the entry up until which the one that is not in the
 130                 // follower's log
 131                 for (int i = 0;
 132                      i < appendEntries.getEntries()
 133                          .size(); i++, addEntriesFrom++) {
 134                     ReplicatedLogEntry matchEntry =
 135                         appendEntries.getEntries().get(i);
 136                     ReplicatedLogEntry newEntry = context.getReplicatedLog()
 137                         .get(matchEntry.getIndex());
 138
 139                     if (newEntry == null) {
 140                         //newEntry not found in the log
 141                         break;
 142                     }
 143
 144                     if (newEntry.getTerm() == matchEntry
 145                         .getTerm()) {
 146                         continue;
 147                     }
 148
 149                     context.getLogger().debug(
 150                         "Removing entries from log starting at "
 151                             + matchEntry.getIndex()
 152                     );
 153
 154                     // Entries do not match so remove all subsequent entries
 155                     context.getReplicatedLog()
 156                         .removeFromAndPersist(matchEntry.getIndex());
 157                     break;
 158                 }
 159             }
 160
 161             context.getLogger().debug(
 162                 "After cleanup entries to be added from = " + (addEntriesFrom
 163                     + lastIndex())
 164             );
 165
 166             // 4. Append any new entries not already in the log
 167             for (int i = addEntriesFrom;
 168                  i < appendEntries.getEntries().size(); i++) {
 169
 170                 context.getLogger().info(
 171                     "Append entry to log " + appendEntries.getEntries().get(
 172                         i).getData()
 173                         .toString()
 174                 );
 175                 context.getReplicatedLog()
 176                     .appendAndPersist(appendEntries.getEntries().get(i));
 177             }
 178
 179             context.getLogger().debug(
 180                 "Log size is now " + context.getReplicatedLog().size());
 181         }
 182
 183
 184         // 5. If leaderCommit > commitIndex, set commitIndex =
 185         // min(leaderCommit, index of last new entry)
 186
 187         long prevCommitIndex = context.getCommitIndex();
 188
 189         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 190             context.getReplicatedLog().lastIndex()));
 191
 192         if (prevCommitIndex != context.getCommitIndex()) {
 193             context.getLogger()
 194                 .debug("Commit index set to " + context.getCommitIndex());
 195         }
 196
 197         // If commitIndex > lastApplied: increment lastApplied, apply
 198         // log[lastApplied] to state machine (§5.3)
 199         if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
 200             applyLogToStateMachine(appendEntries.getLeaderCommit());
 201         }
 202
 203         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 204             lastIndex(), lastTerm()), actor());
 205
 206         return state();
 207     }
 208
 209     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 210         AppendEntriesReply appendEntriesReply) {
 211         return state();
 212     }
 213
 214     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 215         RequestVoteReply requestVoteReply) {
 216         return state();
 217     }
 218
 219     @Override public RaftState state() {
 220         return RaftState.Follower;
 221     }
 222
 223     @Override public RaftState handleMessage(ActorRef sender, Object originalMessage) {
 224
 225         Object message = fromSerializableMessage(originalMessage);
 226
 227         if (message instanceof RaftRPC) {
 228             RaftRPC rpc = (RaftRPC) message;
 229             // If RPC request or response contains term T > currentTerm:
 230             // set currentTerm = T, convert to follower (§5.1)
 231             // This applies to all RPC messages and responses
 232             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 233                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 234             }
 235         }
 236
 237         if (message instanceof ElectionTimeout) {
 238             return RaftState.Candidate;
 239
 240         } else if (message instanceof InstallSnapshot) {
 241             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 242             actor().tell(new ApplySnapshot(installSnapshot.getData()), actor());
 243         }
 244
 245         scheduleElection(electionDuration());
 246
 247         return super.handleMessage(sender, message);
 248     }
 249
 250     @Override public void close() throws Exception {
 251         stopElection();
 252     }
 253 }