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.internal.messages.ApplySnapshot;
  16 import org.opendaylight.controller.cluster.raft.internal.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         // TODO : Refactor this method into a bunch of smaller methods
  44         // to make it easier to read. Before refactoring ensure tests
  45         // cover the code properly
  46
  47         // 1. Reply false if term < currentTerm (§5.1)
  48         // This is handled in the appendEntries method of the base class
  49
  50         // If we got here then we do appear to be talking to the leader
  51         leaderId = appendEntries.getLeaderId();
  52
  53         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
  54         // whose term matches prevLogTerm (§5.3)
  55
  56         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  57             .get(appendEntries.getPrevLogIndex());
  58
  59
  60         boolean outOfSync = true;
  61
  62         // First check if the logs are in sync or not
  63         if (lastIndex() == -1
  64             && appendEntries.getPrevLogIndex() != -1) {
  65
  66             // The follower's log is out of sync because the leader does have
  67             // an entry at prevLogIndex and this follower has no entries in
  68             // it's log.
  69
  70             context.getLogger().debug(
  71                 "The followers log is empty and the senders prevLogIndex is {}",
  72                 appendEntries.getPrevLogIndex());
  73
  74         } else if (lastIndex() > -1
  75             && appendEntries.getPrevLogIndex() != -1
  76             && previousEntry == null) {
  77
  78             // The follower's log is out of sync because the Leader's
  79             // prevLogIndex entry was not found in it's log
  80
  81             context.getLogger().debug(
  82                 "The log is not empty but the prevLogIndex {} was not found in it",
  83                 appendEntries.getPrevLogIndex());
  84
  85         } else if (lastIndex() > -1
  86             && previousEntry != null
  87             && previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
  88
  89             // The follower's log is out of sync because the Leader's
  90             // prevLogIndex entry does exist in the follower's log but it has
  91             // a different term in it
  92
  93             context.getLogger().debug(
  94                 "Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}"
  95                 , previousEntry.getTerm()
  96                 , appendEntries.getPrevLogTerm());
  97         } else {
  98             outOfSync = false;
  99         }
 100
 101         if (outOfSync) {
 102             // We found that the log was out of sync so just send a negative
 103             // reply and return
 104             sender.tell(
 105                 new AppendEntriesReply(context.getId(), currentTerm(), false,
 106                     lastIndex(), lastTerm()), actor()
 107             );
 108             return state();
 109         }
 110
 111         if (appendEntries.getEntries() != null
 112             && appendEntries.getEntries().size() > 0) {
 113             context.getLogger().debug(
 114                 "Number of entries to be appended = " + appendEntries
 115                     .getEntries().size()
 116             );
 117
 118             // 3. If an existing entry conflicts with a new one (same index
 119             // but different terms), delete the existing entry and all that
 120             // follow it (§5.3)
 121             int addEntriesFrom = 0;
 122             if (context.getReplicatedLog().size() > 0) {
 123
 124                 // Find the entry up until which the one that is not in the
 125                 // follower's log
 126                 for (int i = 0;
 127                      i < appendEntries.getEntries()
 128                          .size(); i++, addEntriesFrom++) {
 129                     ReplicatedLogEntry matchEntry =
 130                         appendEntries.getEntries().get(i);
 131                     ReplicatedLogEntry newEntry = context.getReplicatedLog()
 132                         .get(matchEntry.getIndex());
 133
 134                     if (newEntry == null) {
 135                         //newEntry not found in the log
 136                         break;
 137                     }
 138
 139                     if (newEntry.getTerm() == matchEntry
 140                         .getTerm()) {
 141                         continue;
 142                     }
 143
 144                     context.getLogger().debug(
 145                         "Removing entries from log starting at "
 146                             + matchEntry.getIndex()
 147                     );
 148
 149                     // Entries do not match so remove all subsequent entries
 150                     context.getReplicatedLog()
 151                         .removeFromAndPersist(matchEntry.getIndex());
 152                     break;
 153                 }
 154             }
 155
 156             context.getLogger().debug(
 157                 "After cleanup entries to be added from = " + (addEntriesFrom
 158                     + lastIndex())
 159             );
 160
 161             // 4. Append any new entries not already in the log
 162             for (int i = addEntriesFrom;
 163                  i < appendEntries.getEntries().size(); i++) {
 164
 165                 context.getLogger().debug(
 166                     "Append entry to log " + appendEntries.getEntries().get(i).getData()
 167                         .toString()
 168                 );
 169                 context.getReplicatedLog()
 170                     .appendAndPersist(appendEntries.getEntries().get(i));
 171             }
 172
 173             context.getLogger().debug(
 174                 "Log size is now " + context.getReplicatedLog().size());
 175         }
 176
 177
 178         // 5. If leaderCommit > commitIndex, set commitIndex =
 179         // min(leaderCommit, index of last new entry)
 180
 181         long prevCommitIndex = context.getCommitIndex();
 182
 183         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 184             context.getReplicatedLog().lastIndex()));
 185
 186         if (prevCommitIndex != context.getCommitIndex()) {
 187             context.getLogger()
 188                 .debug("Commit index set to " + context.getCommitIndex());
 189         }
 190
 191         // If commitIndex > lastApplied: increment lastApplied, apply
 192         // log[lastApplied] to state machine (§5.3)
 193         if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
 194             applyLogToStateMachine(appendEntries.getLeaderCommit());
 195         }
 196
 197         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 198             lastIndex(), lastTerm()), actor());
 199
 200         return state();
 201     }
 202
 203     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 204         AppendEntriesReply appendEntriesReply) {
 205         return state();
 206     }
 207
 208     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 209         RequestVoteReply requestVoteReply) {
 210         return state();
 211     }
 212
 213     @Override public RaftState state() {
 214         return RaftState.Follower;
 215     }
 216
 217     @Override public RaftState handleMessage(ActorRef sender, Object message) {
 218         if (message instanceof RaftRPC) {
 219             RaftRPC rpc = (RaftRPC) message;
 220             // If RPC request or response contains term T > currentTerm:
 221             // set currentTerm = T, convert to follower (§5.1)
 222             // This applies to all RPC messages and responses
 223             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 224                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 225             }
 226         }
 227
 228         if (message instanceof ElectionTimeout) {
 229             return RaftState.Candidate;
 230         } else if (message instanceof InstallSnapshot) {
 231             InstallSnapshot snapshot = (InstallSnapshot) message;
 232             actor().tell(new ApplySnapshot(snapshot), actor());
 233         }
 234
 235         scheduleElection(electionDuration());
 236
 237         return super.handleMessage(sender, message);
 238     }
 239
 240     @Override public void close() throws Exception {
 241         stopElection();
 242     }
 243 }