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