opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Candidate.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.actor.ActorSelection;
  13 import java.util.ArrayList;
  14 import java.util.Collection;
  15 import org.opendaylight.controller.cluster.raft.PeerInfo;
  16 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  17 import org.opendaylight.controller.cluster.raft.RaftState;
  18 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  19 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  20 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  21 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  22 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  23 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  24
  25 /**
  26  * The behavior of a RaftActor when it is in the CandidateState
  27  * <p/>
  28  * Candidates (§5.2):
  29  * <ul>
  30  * <li> On conversion to candidate, start election:
  31  * <ul>
  32  * <li> Increment currentTerm
  33  * <li> Vote for self
  34  * <li> Reset election timer
  35  * <li> Send RequestVote RPCs to all other servers
  36  * </ul>
  37  * <li> If votes received from majority of servers: become leader
  38  * <li> If AppendEntries RPC received from new leader: convert to
  39  * follower
  40  * <li> If election timeout elapses: start new election
  41  * </ul>
  42  */
  43 public class Candidate extends AbstractRaftActorBehavior {
  44
  45     private int voteCount;
  46
  47     private final int votesRequired;
  48
  49     private final Collection<String> votingPeers = new ArrayList<>();
  50
  51     public Candidate(RaftActorContext context) {
  52         super(context, RaftState.Candidate);
  53
  54         for(PeerInfo peer: context.getPeers()) {
  55             if(peer.isVoting()) {
  56                 votingPeers.add(peer.getId());
  57             }
  58         }
  59
  60         if(LOG.isDebugEnabled()) {
  61             LOG.debug("{}: Election: Candidate has following voting peers: {}", logName(), votingPeers);
  62         }
  63
  64         votesRequired = getMajorityVoteCount(votingPeers.size());
  65
  66         startNewTerm();
  67
  68         if(votingPeers.isEmpty()){
  69             actor().tell(ElectionTimeout.INSTANCE, actor());
  70         } else {
  71             scheduleElection(electionDuration());
  72         }
  73     }
  74
  75     @Override
  76     public final String getLeaderId() {
  77         return null;
  78     }
  79
  80     @Override
  81     public final short getLeaderPayloadVersion() {
  82         return -1;
  83     }
  84
  85     @Override
  86     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
  87         AppendEntries appendEntries) {
  88
  89         if(LOG.isDebugEnabled()) {
  90             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  91         }
  92
  93         // Some other candidate for the same term became a leader and sent us an append entry
  94         if(currentTerm() == appendEntries.getTerm()){
  95             LOG.info("{}: New Leader {} sent an AppendEntries to Candidate for term {} - will switch to Follower",
  96                     logName(), appendEntries.getLeaderId(), currentTerm());
  97
  98             return switchBehavior(new Follower(context));
  99         }
 100
 101         return this;
 102     }
 103
 104     @Override
 105     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 106         return this;
 107     }
 108
 109     @Override
 110     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender, RequestVoteReply requestVoteReply) {
 111         LOG.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply, voteCount);
 112
 113         if (requestVoteReply.isVoteGranted()) {
 114             voteCount++;
 115         }
 116
 117         if (voteCount >= votesRequired) {
 118             if(context.getLastApplied() < context.getReplicatedLog().lastIndex()) {
 119                 LOG.info("{}: LastApplied index {} is behind last index {} - switching to PreLeader",
 120                         logName(), context.getLastApplied(), context.getReplicatedLog().lastIndex());
 121                 return internalSwitchBehavior(RaftState.PreLeader);
 122             } else {
 123                 return internalSwitchBehavior(RaftState.Leader);
 124             }
 125         }
 126
 127         return this;
 128     }
 129
 130     @Override
 131     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 132         if (message instanceof ElectionTimeout) {
 133             LOG.debug("{}: Received ElectionTimeout", logName());
 134
 135             if (votesRequired == 0) {
 136                 // If there are no peers then we should be a Leader
 137                 // We wait for the election timeout to occur before declare
 138                 // ourselves the leader. This gives enough time for a leader
 139                 // who we do not know about (as a peer)
 140                 // to send a message to the candidate
 141
 142                 return internalSwitchBehavior(RaftState.Leader);
 143             }
 144
 145             startNewTerm();
 146             scheduleElection(electionDuration());
 147             return this;
 148         }
 149
 150         if (message instanceof RaftRPC) {
 151
 152             RaftRPC rpc = (RaftRPC) message;
 153
 154             if(LOG.isDebugEnabled()) {
 155                 LOG.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 156                         context.getTermInformation().getCurrentTerm());
 157             }
 158
 159             // If RPC request or response contains term T > currentTerm:
 160             // set currentTerm = T, convert to follower (§5.1)
 161             // This applies to all RPC messages and responses
 162             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 163                 LOG.info("{}: Term {} in \"{}\" message is greater than Candidate's term {} - switching to Follower",
 164                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 165
 166                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 167
 168                 // The raft paper does not say whether or not a Candidate can/should process a RequestVote in
 169                 // this case but doing so gains quicker convergence when the sender's log is more up-to-date.
 170                 if (message instanceof RequestVote) {
 171                     super.handleMessage(sender, message);
 172                 }
 173
 174                 return internalSwitchBehavior(RaftState.Follower);
 175             }
 176         }
 177
 178         return super.handleMessage(sender, message);
 179     }
 180
 181
 182     private void startNewTerm() {
 183
 184
 185         // set voteCount back to 1 (that is voting for self)
 186         voteCount = 1;
 187
 188         // Increment the election term and vote for self
 189         long currentTerm = context.getTermInformation().getCurrentTerm();
 190         long newTerm = currentTerm + 1;
 191         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 192
 193         LOG.info("{}: Starting new election term {}", logName(), newTerm);
 194
 195         // Request for a vote
 196         // TODO: Retry request for vote if replies do not arrive in a reasonable
 197         // amount of time TBD
 198         for (String peerId : votingPeers) {
 199             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 200             if(peerActor != null) {
 201                 RequestVote requestVote = new RequestVote(
 202                         context.getTermInformation().getCurrentTerm(),
 203                         context.getId(),
 204                         context.getReplicatedLog().lastIndex(),
 205                         context.getReplicatedLog().lastTerm());
 206
 207                 LOG.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 208
 209                 peerActor.tell(requestVote, context.getActor());
 210             }
 211         }
 212     }
 213
 214     @Override
 215     public void close() {
 216         stopElection();
 217     }
 218 }