opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.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.annotations.VisibleForTesting;
  13 import com.google.common.base.Preconditions;
  14 import com.google.common.base.Stopwatch;
  15 import java.util.concurrent.TimeUnit;
  16 import javax.annotation.Nonnull;
  17 import javax.annotation.Nullable;
  18 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  19 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  20 import org.opendaylight.controller.cluster.raft.RaftActorLeadershipTransferCohort;
  21 import org.opendaylight.controller.cluster.raft.RaftState;
  22 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  23 import org.opendaylight.controller.cluster.raft.base.messages.IsolatedLeaderCheck;
  24 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  25
  26 /**
  27  * The behavior of a RaftActor when it is in the Leader state
  28  * <p/>
  29  * Leaders:
  30  * <ul>
  31  * <li> Upon election: send initial empty AppendEntries RPCs
  32  * (heartbeat) to each server; repeat during idle periods to
  33  * prevent election timeouts (§5.2)
  34  * <li> If command received from client: append entry to local log,
  35  * respond after entry applied to state machine (§5.3)
  36  * <li> If last log index ≥ nextIndex for a follower: send
  37  * AppendEntries RPC with log entries starting at nextIndex
  38  * <ul>
  39  * <li> If successful: update nextIndex and matchIndex for
  40  * follower (§5.3)
  41  * <li> If AppendEntries fails because of log inconsistency:
  42  * decrement nextIndex and retry (§5.3)
  43  * </ul>
  44  * <li> If there exists an N such that N > commitIndex, a majority
  45  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  46  * set commitIndex = N (§5.3, §5.4).
  47  */
  48 public class Leader extends AbstractLeader {
  49     private static final IsolatedLeaderCheck ISOLATED_LEADER_CHECK = new IsolatedLeaderCheck();
  50     private final Stopwatch isolatedLeaderCheck;
  51     private @Nullable LeadershipTransferContext leadershipTransferContext;
  52
  53     public Leader(RaftActorContext context) {
  54         super(context);
  55         isolatedLeaderCheck = Stopwatch.createStarted();
  56     }
  57
  58     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
  59         Preconditions.checkNotNull(sender, "sender should not be null");
  60
  61         if (originalMessage instanceof IsolatedLeaderCheck) {
  62             if (isLeaderIsolated()) {
  63                 LOG.warn("{}: At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
  64                         context.getId(), getMinIsolatedLeaderPeerCount(), leaderId);
  65
  66                 return internalSwitchBehavior(RaftState.IsolatedLeader);
  67             }
  68         }
  69
  70         return super.handleMessage(sender, originalMessage);
  71     }
  72
  73     @Override
  74     protected void beforeSendHeartbeat(){
  75         if(isolatedLeaderCheck.elapsed(TimeUnit.MILLISECONDS) > context.getConfigParams().getIsolatedCheckIntervalInMillis()){
  76             context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
  77             isolatedLeaderCheck.reset().start();
  78         }
  79
  80         if(leadershipTransferContext != null && leadershipTransferContext.isExpired(
  81                 context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
  82             LOG.debug("{}: Leadership transfer expired", logName());
  83             leadershipTransferContext = null;
  84         }
  85     }
  86
  87     @Override
  88     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
  89         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
  90         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
  91         return returnBehavior;
  92     }
  93
  94     /**
  95      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
  96      * <ul>
  97      * <li>Start a timer (Stopwatch).</li>
  98      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
  99      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
 100      * <li>If it matches, </li>
 101      *   <ul>
 102      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
 103      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
 104      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
 105      *   </ul>
 106      * <li>Otherwise if the election time out period elapses, notify
 107      *     {@link RaftActorLeadershipTransferCohort#abortTtransfer}.</li>
 108      * </ul>
 109      *
 110      * @param leadershipTransferCohort
 111      */
 112     public void transferLeadership(@Nonnull RaftActorLeadershipTransferCohort leadershipTransferCohort) {
 113         LOG.debug("{}: Attempting to transfer leadership", logName());
 114
 115         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
 116
 117         // Send an immediate heart beat to the followers.
 118         sendAppendEntries(0, false);
 119     }
 120
 121     private void tryToCompleteLeadershipTransfer(String followerId) {
 122         if(leadershipTransferContext == null) {
 123             return;
 124         }
 125
 126         FollowerLogInformation followerInfo = getFollower(followerId);
 127         if(followerInfo == null) {
 128             return;
 129         }
 130
 131         long lastIndex = context.getReplicatedLog().lastIndex();
 132         boolean isVoting = context.getPeerInfo(followerId).isVoting();
 133
 134         LOG.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
 135                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
 136
 137         if(isVoting && followerInfo.getMatchIndex() == lastIndex) {
 138             LOG.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
 139
 140             // We can't be sure if the follower has applied all its log entries to its state so send an
 141             // additional AppendEntries with the latest commit index.
 142             sendAppendEntries(0, false);
 143
 144             // Now send an ElectionTimeout to the matching follower to immediately start an election.
 145             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 146             followerActor.tell(ElectionTimeout.INSTANCE, context.getActor());
 147
 148             LOG.debug("{}: Leader transfer complete", logName());
 149
 150             leadershipTransferContext.transferCohort.transferComplete();
 151             leadershipTransferContext = null;
 152         }
 153     }
 154
 155     @Override
 156     public void close() throws Exception {
 157         if(leadershipTransferContext != null) {
 158             leadershipTransferContext.transferCohort.abortTransfer();
 159         }
 160
 161         super.close();
 162     }
 163
 164     @VisibleForTesting
 165     void markFollowerActive(String followerId) {
 166         getFollower(followerId).markFollowerActive();
 167     }
 168
 169     @VisibleForTesting
 170     void markFollowerInActive(String followerId) {
 171         getFollower(followerId).markFollowerInActive();
 172     }
 173
 174     private static class LeadershipTransferContext {
 175         RaftActorLeadershipTransferCohort transferCohort;
 176         Stopwatch timer = Stopwatch.createStarted();
 177
 178         LeadershipTransferContext(RaftActorLeadershipTransferCohort transferCohort) {
 179             this.transferCohort = transferCohort;
 180         }
 181
 182         boolean isExpired(long timeout) {
 183             if(timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
 184                 transferCohort.abortTransfer();
 185                 return true;
 186             }
 187
 188             return false;
 189         }
 190     }
 191 }