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  * <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         log.debug("{}: Election: Candidate has following voting peers: {}", logName(), votingPeers);
  61
  62         votesRequired = getMajorityVoteCount(votingPeers.size());
  63
  64         startNewTerm();
  65
  66         if (votingPeers.isEmpty()) {
  67             actor().tell(ElectionTimeout.INSTANCE, actor());
  68         } else {
  69             scheduleElection(electionDuration());
  70         }
  71     }
  72
  73     @Override
  74     public final String getLeaderId() {
  75         return null;
  76     }
  77
  78     @Override
  79     public final short getLeaderPayloadVersion() {
  80         return -1;
  81     }
  82
  83     @Override
  84     protected RaftActorBehavior handleAppendEntries(ActorRef sender, AppendEntries appendEntries) {
  85
  86         log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  87
  88         // Some other candidate for the same term became a leader and sent us an append entry
  89         if (currentTerm() == appendEntries.getTerm()) {
  90             log.debug("{}: New Leader sent an append entry to Candidate for term {} will switch to Follower",
  91                     logName(), currentTerm());
  92
  93             return switchBehavior(new Follower(context));
  94         }
  95
  96         return this;
  97     }
  98
  99     @Override
 100     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 101         return this;
 102     }
 103
 104     @Override
 105     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender, 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.debug("{}: LastApplied index {} is behind last index {}", logName(), context.getLastApplied(),
 115                         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     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 127         if (message instanceof ElectionTimeout) {
 128             log.debug("{}: Received ElectionTimeout", logName());
 129
 130             if (votesRequired == 0) {
 131                 // If there are no peers then we should be a Leader
 132                 // We wait for the election timeout to occur before declare
 133                 // ourselves the leader. This gives enough time for a leader
 134                 // who we do not know about (as a peer)
 135                 // to send a message to the candidate
 136
 137                 return internalSwitchBehavior(RaftState.Leader);
 138             }
 139
 140             startNewTerm();
 141             scheduleElection(electionDuration());
 142             return this;
 143         }
 144
 145         if (message instanceof RaftRPC) {
 146
 147             RaftRPC rpc = (RaftRPC) message;
 148
 149             log.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 150                         context.getTermInformation().getCurrentTerm());
 151
 152             // If RPC request or response contains term T > currentTerm:
 153             // set currentTerm = T, convert to follower (§5.1)
 154             // This applies to all RPC messages and responses
 155             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 156                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 157
 158                 // The raft paper does not say whether or not a Candidate can/should process a RequestVote in
 159                 // this case but doing so gains quicker convergence when the sender's log is more up-to-date.
 160                 if (message instanceof RequestVote) {
 161                     super.handleMessage(sender, message);
 162                 }
 163
 164                 return internalSwitchBehavior(RaftState.Follower);
 165             }
 166         }
 167
 168         return super.handleMessage(sender, message);
 169     }
 170
 171
 172     private void startNewTerm() {
 173
 174
 175         // set voteCount back to 1 (that is voting for self)
 176         voteCount = 1;
 177
 178         // Increment the election term and vote for self
 179         long currentTerm = context.getTermInformation().getCurrentTerm();
 180         long newTerm = currentTerm + 1;
 181         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 182
 183         log.debug("{}: Starting new term {}", logName(), newTerm);
 184
 185         // Request for a vote
 186         // TODO: Retry request for vote if replies do not arrive in a reasonable
 187         // amount of time TBD
 188         for (String peerId : votingPeers) {
 189             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 190             if (peerActor != null) {
 191                 RequestVote requestVote = new RequestVote(
 192                         context.getTermInformation().getCurrentTerm(),
 193                         context.getId(),
 194                         context.getReplicatedLog().lastIndex(),
 195                         context.getReplicatedLog().lastTerm());
 196
 197                 log.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 198
 199                 peerActor.tell(requestVote, context.getActor());
 200             }
 201         }
 202     }
 203
 204     @Override
 205     public void close() {
 206         stopElection();
 207     }
 208 }