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 follower's log
 130                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 131                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 132                     ReplicatedLogEntry newEntry = context.getReplicatedLog().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().info(
 166                     "Append entry to log " + appendEntries.getEntries().get(
 167                         i).getData()
 168                         .toString()
 169                 );
 170                 context.getReplicatedLog()
 171                     .appendAndPersist(appendEntries.getEntries().get(i));
 172             }
 173
 174             context.getLogger().debug(
 175                 "Log size is now " + context.getReplicatedLog().size());
 176         }
 177
 178
 179         // 5. If leaderCommit > commitIndex, set commitIndex =
 180         // min(leaderCommit, index of last new entry)
 181
 182         long prevCommitIndex = context.getCommitIndex();
 183
 184         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 185             context.getReplicatedLog().lastIndex()));
 186
 187         if (prevCommitIndex != context.getCommitIndex()) {
 188             context.getLogger()
 189                 .debug("Commit index set to " + context.getCommitIndex());
 190         }
 191
 192         // If commitIndex > lastApplied: increment lastApplied, apply
 193         // log[lastApplied] to state machine (§5.3)
 194         if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
 195             applyLogToStateMachine(appendEntries.getLeaderCommit());
 196         }
 197
 198         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 199             lastIndex(), lastTerm()), actor());
 200
 201         return state();
 202     }
 203
 204     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 205         AppendEntriesReply appendEntriesReply) {
 206         return state();
 207     }
 208
 209     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 210         RequestVoteReply requestVoteReply) {
 211         return state();
 212     }
 213
 214     @Override public RaftState state() {
 215         return RaftState.Follower;
 216     }
 217
 218     @Override public RaftState handleMessage(ActorRef sender, Object originalMessage) {
 219
 220         Object message = fromSerializableMessage(originalMessage);
 221
 222         if (message instanceof RaftRPC) {
 223             RaftRPC rpc = (RaftRPC) message;
 224             // If RPC request or response contains term T > currentTerm:
 225             // set currentTerm = T, convert to follower (§5.1)
 226             // This applies to all RPC messages and responses
 227             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 228                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 229             }
 230         }
 231
 232         if (message instanceof ElectionTimeout) {
 233             return RaftState.Candidate;
 234
 235         } else if (message instanceof InstallSnapshot) {
 236             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 237             actor().tell(new ApplySnapshot(installSnapshot.getData()), actor());
 238         }
 239
 240         scheduleElection(electionDuration());
 241
 242         return super.handleMessage(sender, message);
 243     }
 244
 245     @Override public void close() throws Exception {
 246         stopElection();
 247     }
 248 }