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 java.util.ArrayList;
  13 import java.util.Collection;
  14 import org.opendaylight.controller.cluster.raft.PeerInfo;
  15 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  16 import org.opendaylight.controller.cluster.raft.RaftState;
  17 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  18 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  19 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  20 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  21 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  22 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  23 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  24 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  25 import scala.concurrent.duration.FiniteDuration;
  26
  27 /**
  28  * The behavior of a RaftActor when it is in the Candidate raft state.
  29  *
  30  * <p>
  31  * Candidates (§5.2):
  32  * <ul>
  33  * <li> On conversion to candidate, start election:
  34  * <ul>
  35  * <li> Increment currentTerm
  36  * <li> Vote for self
  37  * <li> Reset election timer
  38  * <li> Send RequestVote RPCs to all other servers
  39  * </ul>
  40  * <li> If votes received from majority of servers: become leader
  41  * <li> If AppendEntries RPC received from new leader: convert to
  42  * follower
  43  * <li> If election timeout elapses: start new election
  44  * </ul>
  45  */
  46 public final class Candidate extends AbstractRaftActorBehavior {
  47
  48     private int voteCount;
  49
  50     private final int votesRequired;
  51
  52     private final Collection<String> votingPeers = new ArrayList<>();
  53
  54     public Candidate(final RaftActorContext context) {
  55         super(context, RaftState.Candidate);
  56
  57         for (PeerInfo peer: context.getPeers()) {
  58             if (peer.isVoting()) {
  59                 votingPeers.add(peer.getId());
  60             }
  61         }
  62
  63         log.debug("{}: Election: Candidate has following voting peers: {}", logName(), votingPeers);
  64
  65         votesRequired = getMajorityVoteCount(votingPeers.size());
  66
  67         startNewTerm();
  68
  69         if (votingPeers.isEmpty()) {
  70             actor().tell(ElectionTimeout.INSTANCE, actor());
  71         } else {
  72             scheduleElection(electionDuration());
  73         }
  74     }
  75
  76     @Override
  77     public String getLeaderId() {
  78         return null;
  79     }
  80
  81     @Override
  82     public short getLeaderPayloadVersion() {
  83         return -1;
  84     }
  85
  86     @Override
  87     protected RaftActorBehavior handleAppendEntries(final ActorRef sender, final AppendEntries appendEntries) {
  88
  89         log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  90
  91         // Some other candidate for the same term became a leader and sent us an append entry
  92         if (currentTerm() == appendEntries.getTerm()) {
  93             log.info("{}: New Leader {} sent an AppendEntries to Candidate for term {} - will switch to Follower",
  94                     logName(), appendEntries.getLeaderId(), currentTerm());
  95
  96             return switchBehavior(new Follower(context));
  97         }
  98
  99         return this;
 100     }
 101
 102     @Override
 103     protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
 104             final AppendEntriesReply appendEntriesReply) {
 105         return this;
 106     }
 107
 108     @Override
 109     protected RaftActorBehavior handleRequestVoteReply(final ActorRef sender, final RequestVoteReply requestVoteReply) {
 110         log.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply, voteCount);
 111
 112         if (requestVoteReply.isVoteGranted()) {
 113             voteCount++;
 114         }
 115
 116         if (voteCount >= votesRequired) {
 117             if (context.getLastApplied() < context.getReplicatedLog().lastIndex()) {
 118                 log.info("{}: LastApplied index {} is behind last index {} - switching to PreLeader",
 119                         logName(), context.getLastApplied(), context.getReplicatedLog().lastIndex());
 120                 return internalSwitchBehavior(RaftState.PreLeader);
 121             } else {
 122                 return internalSwitchBehavior(RaftState.Leader);
 123             }
 124         }
 125
 126         return this;
 127     }
 128
 129     @Override
 130     protected FiniteDuration electionDuration() {
 131         return super.electionDuration().$div(context.getConfigParams().getCandidateElectionTimeoutDivisor());
 132     }
 133
 134
 135     @Override
 136     ApplyState getApplyStateFor(final ReplicatedLogEntry entry) {
 137         throw new IllegalStateException("A candidate should never attempt to apply " + entry);
 138     }
 139
 140     @Override
 141     public RaftActorBehavior handleMessage(final ActorRef sender, final Object message) {
 142         if (message instanceof ElectionTimeout) {
 143             log.debug("{}: Received ElectionTimeout", logName());
 144
 145             if (votesRequired == 0) {
 146                 // If there are no peers then we should be a Leader
 147                 // We wait for the election timeout to occur before declare
 148                 // ourselves the leader. This gives enough time for a leader
 149                 // who we do not know about (as a peer)
 150                 // to send a message to the candidate
 151
 152                 return internalSwitchBehavior(RaftState.Leader);
 153             }
 154
 155             startNewTerm();
 156             scheduleElection(electionDuration());
 157             return this;
 158         }
 159
 160         if (message instanceof RaftRPC) {
 161
 162             RaftRPC rpc = (RaftRPC) message;
 163
 164             log.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 165                         context.getTermInformation().getCurrentTerm());
 166
 167             // If RPC request or response contains term T > currentTerm:
 168             // set currentTerm = T, convert to follower (§5.1)
 169             // This applies to all RPC messages and responses
 170             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 171                 log.info("{}: Term {} in \"{}\" message is greater than Candidate's term {} - switching to Follower",
 172                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 173
 174                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 175
 176                 // The raft paper does not say whether or not a Candidate can/should process a RequestVote in
 177                 // this case but doing so gains quicker convergence when the sender's log is more up-to-date.
 178                 if (message instanceof RequestVote) {
 179                     super.handleMessage(sender, message);
 180                 }
 181
 182                 return internalSwitchBehavior(RaftState.Follower);
 183             }
 184         }
 185
 186         return super.handleMessage(sender, message);
 187     }
 188
 189     private void startNewTerm() {
 190         // set voteCount back to 1 (that is voting for self)
 191         voteCount = 1;
 192
 193         // Increment the election term and vote for self
 194         long currentTerm = context.getTermInformation().getCurrentTerm();
 195         long newTerm = currentTerm + 1;
 196         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 197
 198         log.info("{}: Starting new election term {}", logName(), newTerm);
 199
 200         // Request for a vote
 201         // TODO: Retry request for vote if replies do not arrive in a reasonable
 202         // amount of time TBD
 203         for (String peerId : votingPeers) {
 204             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 205             if (peerActor != null) {
 206                 RequestVote requestVote = new RequestVote(
 207                         context.getTermInformation().getCurrentTerm(),
 208                         context.getId(),
 209                         context.getReplicatedLog().lastIndex(),
 210                         context.getReplicatedLog().lastTerm());
 211
 212                 log.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 213
 214                 peerActor.tell(requestVote, context.getActor());
 215             }
 216         }
 217     }
 218
 219     @Override
 220     public void close() {
 221         stopElection();
 222     }
 223 }