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 package org.opendaylight.controller.cluster.raft.behaviors;
   9
  10 import akka.actor.ActorRef;
  11 import akka.actor.ActorSelection;
  12 import com.google.common.collect.ImmutableList;
  13 import org.opendaylight.controller.cluster.raft.PeerInfo;
  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.base.messages.ApplyState;
  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 import scala.concurrent.duration.FiniteDuration;
  25
  26 /**
  27  * The behavior of a RaftActor when it is in the Candidate raft state.
  28  *
  29  * <p>
  30  * Candidates (§5.2):
  31  * <ul>
  32  * <li> On conversion to candidate, start election:
  33  * <ul>
  34  * <li> Increment currentTerm
  35  * <li> Vote for self
  36  * <li> Reset election timer
  37  * <li> Send RequestVote RPCs to all other servers
  38  * </ul>
  39  * <li> If votes received from majority of servers: become leader
  40  * <li> If AppendEntries RPC received from new leader: convert to
  41  * follower
  42  * <li> If election timeout elapses: start new election
  43  * </ul>
  44  */
  45 public final class Candidate extends AbstractRaftActorBehavior {
  46     private final ImmutableList<String> votingPeers;
  47     private final int votesRequired;
  48
  49     private int voteCount;
  50
  51     public Candidate(final RaftActorContext context) {
  52         super(context, RaftState.Candidate);
  53
  54         votingPeers = context.getPeers().stream()
  55             .filter(PeerInfo::isVoting)
  56             .map(PeerInfo::getId)
  57             .collect(ImmutableList.toImmutableList());
  58
  59         log.debug("{}: Election: Candidate has following voting peers: {}", logName(), votingPeers);
  60
  61         votesRequired = getMajorityVoteCount(votingPeers.size());
  62
  63         startNewTerm();
  64
  65         if (votingPeers.isEmpty()) {
  66             actor().tell(ElectionTimeout.INSTANCE, actor());
  67         } else {
  68             scheduleElection(electionDuration());
  69         }
  70     }
  71
  72     @Override
  73     public String getLeaderId() {
  74         return null;
  75     }
  76
  77     @Override
  78     public short getLeaderPayloadVersion() {
  79         return -1;
  80     }
  81
  82     @Override
  83     protected RaftActorBehavior handleAppendEntries(final ActorRef sender, final AppendEntries appendEntries) {
  84
  85         log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  86
  87         // Some other candidate for the same term became a leader and sent us an append entry
  88         if (currentTerm() == appendEntries.getTerm()) {
  89             log.info("{}: New Leader {} sent an AppendEntries to Candidate for term {} - will switch to Follower",
  90                     logName(), appendEntries.getLeaderId(), currentTerm());
  91
  92             return switchBehavior(new Follower(context));
  93         }
  94
  95         return this;
  96     }
  97
  98     @Override
  99     protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
 100             final AppendEntriesReply appendEntriesReply) {
 101         return this;
 102     }
 103
 104     @Override
 105     protected RaftActorBehavior handleRequestVoteReply(final ActorRef sender, final RequestVoteReply requestVoteReply) {
 106         log.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply, voteCount);
 107
 108         if (requestVoteReply.isVoteGranted()) {
 109             voteCount++;
 110         }
 111
 112         if (voteCount >= votesRequired) {
 113             if (context.getLastApplied() < context.getReplicatedLog().lastIndex()) {
 114                 log.info("{}: LastApplied index {} is behind last index {} - switching to PreLeader",
 115                         logName(), context.getLastApplied(), context.getReplicatedLog().lastIndex());
 116                 return internalSwitchBehavior(RaftState.PreLeader);
 117             } else {
 118                 return internalSwitchBehavior(RaftState.Leader);
 119             }
 120         }
 121
 122         return this;
 123     }
 124
 125     @Override
 126     protected FiniteDuration electionDuration() {
 127         return super.electionDuration().$div(context.getConfigParams().getCandidateElectionTimeoutDivisor());
 128     }
 129
 130
 131     @Override
 132     ApplyState getApplyStateFor(final ReplicatedLogEntry entry) {
 133         throw new IllegalStateException("A candidate should never attempt to apply " + entry);
 134     }
 135
 136     @Override
 137     public RaftActorBehavior handleMessage(final ActorRef sender, final Object message) {
 138         if (message instanceof ElectionTimeout) {
 139             log.debug("{}: Received ElectionTimeout", logName());
 140
 141             if (votesRequired == 0) {
 142                 // If there are no peers then we should be a Leader
 143                 // We wait for the election timeout to occur before declare
 144                 // ourselves the leader. This gives enough time for a leader
 145                 // who we do not know about (as a peer)
 146                 // to send a message to the candidate
 147
 148                 return internalSwitchBehavior(RaftState.Leader);
 149             }
 150
 151             startNewTerm();
 152             scheduleElection(electionDuration());
 153             return this;
 154         }
 155
 156         if (message instanceof RaftRPC rpc) {
 157
 158             log.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 159                         context.getTermInformation().getCurrentTerm());
 160
 161             // If RPC request or response contains term T > currentTerm:
 162             // set currentTerm = T, convert to follower (§5.1)
 163             // This applies to all RPC messages and responses
 164             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 165                 log.info("{}: Term {} in \"{}\" message is greater than Candidate's term {} - switching to Follower",
 166                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 167
 168                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 169
 170                 // The raft paper does not say whether or not a Candidate can/should process a RequestVote in
 171                 // this case but doing so gains quicker convergence when the sender's log is more up-to-date.
 172                 if (message instanceof RequestVote) {
 173                     super.handleMessage(sender, message);
 174                 }
 175
 176                 return internalSwitchBehavior(RaftState.Follower);
 177             }
 178         }
 179
 180         return super.handleMessage(sender, message);
 181     }
 182
 183     private void startNewTerm() {
 184         // set voteCount back to 1 (that is voting for self)
 185         voteCount = 1;
 186
 187         // Increment the election term and vote for self
 188         long currentTerm = context.getTermInformation().getCurrentTerm();
 189         long newTerm = currentTerm + 1;
 190         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 191
 192         log.info("{}: Starting new election term {}", logName(), newTerm);
 193
 194         // Request for a vote
 195         // TODO: Retry request for vote if replies do not arrive in a reasonable
 196         // amount of time TBD
 197         for (String peerId : votingPeers) {
 198             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 199             if (peerActor != null) {
 200                 RequestVote requestVote = new RequestVote(
 201                         context.getTermInformation().getCurrentTerm(),
 202                         context.getId(),
 203                         context.getReplicatedLog().lastIndex(),
 204                         context.getReplicatedLog().lastTerm());
 205
 206                 log.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 207
 208                 peerActor.tell(requestVote, context.getActor());
 209             }
 210         }
 211     }
 212
 213     @Override
 214     public void close() {
 215         stopElection();
 216     }
 217 }