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.messages.AppendEntriesReply;
  24
  25 /**
  26  * The behavior of a RaftActor when it is in the Leader state
  27  * <p/>
  28  * Leaders:
  29  * <ul>
  30  * <li> Upon election: send initial empty AppendEntries RPCs
  31  * (heartbeat) to each server; repeat during idle periods to
  32  * prevent election timeouts (§5.2)
  33  * <li> If command received from client: append entry to local log,
  34  * respond after entry applied to state machine (§5.3)
  35  * <li> If last log index ≥ nextIndex for a follower: send
  36  * AppendEntries RPC with log entries starting at nextIndex
  37  * <ul>
  38  * <li> If successful: update nextIndex and matchIndex for
  39  * follower (§5.3)
  40  * <li> If AppendEntries fails because of log inconsistency:
  41  * decrement nextIndex and retry (§5.3)
  42  * </ul>
  43  * <li> If there exists an N such that N > commitIndex, a majority
  44  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  45  * set commitIndex = N (§5.3, §5.4).
  46  */
  47 public class Leader extends AbstractLeader {
  48     /**
  49      * Internal message sent to periodically check if this leader has become isolated and should transition
  50      * to {@link IsolatedLeader}.
  51      */
  52     @VisibleForTesting
  53     static final Object ISOLATED_LEADER_CHECK = new Object();
  54
  55     private final Stopwatch isolatedLeaderCheck;
  56     private @Nullable LeadershipTransferContext leadershipTransferContext;
  57
  58     public Leader(RaftActorContext context) {
  59         super(context, RaftState.Leader);
  60         isolatedLeaderCheck = Stopwatch.createStarted();
  61     }
  62
  63     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
  64         Preconditions.checkNotNull(sender, "sender should not be null");
  65
  66         if (ISOLATED_LEADER_CHECK.equals(originalMessage)) {
  67             if (isLeaderIsolated()) {
  68                 LOG.warn("{}: At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
  69                         context.getId(), getMinIsolatedLeaderPeerCount(), leaderId);
  70
  71                 return internalSwitchBehavior(RaftState.IsolatedLeader);
  72             }
  73         }
  74
  75         return super.handleMessage(sender, originalMessage);
  76     }
  77
  78     @Override
  79     protected void beforeSendHeartbeat(){
  80         if(isolatedLeaderCheck.elapsed(TimeUnit.MILLISECONDS) > context.getConfigParams().getIsolatedCheckIntervalInMillis()){
  81             context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
  82             isolatedLeaderCheck.reset().start();
  83         }
  84
  85         if(leadershipTransferContext != null && leadershipTransferContext.isExpired(
  86                 context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
  87             LOG.debug("{}: Leadership transfer expired", logName());
  88             leadershipTransferContext = null;
  89         }
  90     }
  91
  92     @Override
  93     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
  94         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
  95         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
  96         return returnBehavior;
  97     }
  98
  99     /**
 100      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
 101      * <ul>
 102      * <li>Start a timer (Stopwatch).</li>
 103      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
 104      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
 105      * <li>If it matches, </li>
 106      *   <ul>
 107      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
 108      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
 109      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
 110      *   </ul>
 111      * <li>Otherwise if the election time out period elapses, notify
 112      *     {@link RaftActorLeadershipTransferCohort#abortTtransfer}.</li>
 113      * </ul>
 114      *
 115      * @param leadershipTransferCohort
 116      */
 117     public void transferLeadership(@Nonnull RaftActorLeadershipTransferCohort leadershipTransferCohort) {
 118         LOG.debug("{}: Attempting to transfer leadership", logName());
 119
 120         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
 121
 122         // Send an immediate heart beat to the followers.
 123         sendAppendEntries(0, false);
 124     }
 125
 126     private void tryToCompleteLeadershipTransfer(String followerId) {
 127         if(leadershipTransferContext == null) {
 128             return;
 129         }
 130
 131         FollowerLogInformation followerInfo = getFollower(followerId);
 132         if(followerInfo == null) {
 133             return;
 134         }
 135
 136         long lastIndex = context.getReplicatedLog().lastIndex();
 137         boolean isVoting = context.getPeerInfo(followerId).isVoting();
 138
 139         LOG.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
 140                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
 141
 142         if(isVoting && followerInfo.getMatchIndex() == lastIndex) {
 143             LOG.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
 144
 145             // We can't be sure if the follower has applied all its log entries to its state so send an
 146             // additional AppendEntries with the latest commit index.
 147             sendAppendEntries(0, false);
 148
 149             // Now send an ElectionTimeout to the matching follower to immediately start an election.
 150             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 151             followerActor.tell(ElectionTimeout.INSTANCE, context.getActor());
 152
 153             LOG.debug("{}: Leader transfer complete", logName());
 154
 155             leadershipTransferContext.transferCohort.transferComplete();
 156             leadershipTransferContext = null;
 157         }
 158     }
 159
 160     @Override
 161     public void close() {
 162         if(leadershipTransferContext != null) {
 163             leadershipTransferContext.transferCohort.abortTransfer();
 164         }
 165
 166         super.close();
 167     }
 168
 169     @VisibleForTesting
 170     void markFollowerActive(String followerId) {
 171         getFollower(followerId).markFollowerActive();
 172     }
 173
 174     @VisibleForTesting
 175     void markFollowerInActive(String followerId) {
 176         getFollower(followerId).markFollowerInActive();
 177     }
 178
 179     private static class LeadershipTransferContext {
 180         RaftActorLeadershipTransferCohort transferCohort;
 181         Stopwatch timer = Stopwatch.createStarted();
 182
 183         LeadershipTransferContext(RaftActorLeadershipTransferCohort transferCohort) {
 184             this.transferCohort = transferCohort;
 185         }
 186
 187         boolean isExpired(long timeout) {
 188             if(timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
 189                 transferCohort.abortTransfer();
 190                 return true;
 191             }
 192
 193             return false;
 194         }
 195     }
 196 }