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.TimeoutNow;
  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  *
  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  * <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  * <li> If there exists an N such that N &gt; commitIndex, a majority
  43  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  44  * set commitIndex = N (§5.3, §5.4).
  45  * </ul>
  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 = Stopwatch.createStarted();
  56     @Nullable private LeadershipTransferContext leadershipTransferContext;
  57
  58     Leader(RaftActorContext context, @Nullable AbstractLeader initializeFromLeader) {
  59         super(context, RaftState.Leader, initializeFromLeader);
  60     }
  61
  62     public Leader(RaftActorContext context) {
  63         this(context, null);
  64     }
  65
  66     @Override
  67     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
  68         Preconditions.checkNotNull(sender, "sender should not be null");
  69
  70         if (ISOLATED_LEADER_CHECK.equals(originalMessage)) {
  71             if (isLeaderIsolated()) {
  72                 log.warn("{}: At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
  73                     context.getId(), getMinIsolatedLeaderPeerCount(), getLeaderId());
  74                 return internalSwitchBehavior(new IsolatedLeader(context, this));
  75             } else {
  76                 return this;
  77             }
  78         } else {
  79             return super.handleMessage(sender, originalMessage);
  80         }
  81     }
  82
  83     @Override
  84     protected void beforeSendHeartbeat() {
  85         if (isolatedLeaderCheck.elapsed(TimeUnit.MILLISECONDS)
  86                 > context.getConfigParams().getIsolatedCheckIntervalInMillis()) {
  87             context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
  88             isolatedLeaderCheck.reset().start();
  89         }
  90
  91         if (leadershipTransferContext != null && leadershipTransferContext.isExpired(
  92                 context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
  93             log.debug("{}: Leadership transfer expired", logName());
  94             leadershipTransferContext = null;
  95         }
  96     }
  97
  98     @Override
  99     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 100         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
 101         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
 102         return returnBehavior;
 103     }
 104
 105     /**
 106      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
 107      * <ul>
 108      * <li>Start a timer (Stopwatch).</li>
 109      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
 110      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
 111      * <li>If it matches,
 112      *   <ul>
 113      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
 114      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
 115      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
 116      *   </ul></li>
 117      * <li>Otherwise if the election time out period elapses, notify
 118      *     {@link RaftActorLeadershipTransferCohort#abortTransfer}.</li>
 119      * </ul>
 120      *
 121      * @param leadershipTransferCohort the cohort participating in the leadership transfer
 122      */
 123     public void transferLeadership(@Nonnull RaftActorLeadershipTransferCohort leadershipTransferCohort) {
 124         log.debug("{}: Attempting to transfer leadership", logName());
 125
 126         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
 127
 128         // Send an immediate heart beat to the followers.
 129         sendAppendEntries(0, false);
 130     }
 131
 132     private void tryToCompleteLeadershipTransfer(String followerId) {
 133         if (leadershipTransferContext == null) {
 134             return;
 135         }
 136
 137         FollowerLogInformation followerInfo = getFollower(followerId);
 138         if (followerInfo == null) {
 139             return;
 140         }
 141
 142         long lastIndex = context.getReplicatedLog().lastIndex();
 143         boolean isVoting = context.getPeerInfo(followerId).isVoting();
 144
 145         log.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
 146                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
 147
 148         if (isVoting && followerInfo.getMatchIndex() == lastIndex) {
 149             log.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
 150
 151             // We can't be sure if the follower has applied all its log entries to its state so send an
 152             // additional AppendEntries with the latest commit index.
 153             sendAppendEntries(0, false);
 154
 155             // Now send a TimeoutNow message to the matching follower to immediately start an election.
 156             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 157             followerActor.tell(TimeoutNow.INSTANCE, context.getActor());
 158
 159             log.debug("{}: Leader transfer complete", logName());
 160
 161             leadershipTransferContext.transferCohort.transferComplete();
 162             leadershipTransferContext = null;
 163         }
 164     }
 165
 166     @Override
 167     public void close() {
 168         if (leadershipTransferContext != null) {
 169             LeadershipTransferContext localLeadershipTransferContext = leadershipTransferContext;
 170             leadershipTransferContext = null;
 171             localLeadershipTransferContext.transferCohort.abortTransfer();
 172         }
 173
 174         super.close();
 175     }
 176
 177     @VisibleForTesting
 178     void markFollowerActive(String followerId) {
 179         getFollower(followerId).markFollowerActive();
 180     }
 181
 182     @VisibleForTesting
 183     void markFollowerInActive(String followerId) {
 184         getFollower(followerId).markFollowerInActive();
 185     }
 186
 187     private static class LeadershipTransferContext {
 188         RaftActorLeadershipTransferCohort transferCohort;
 189         Stopwatch timer = Stopwatch.createStarted();
 190
 191         LeadershipTransferContext(RaftActorLeadershipTransferCohort transferCohort) {
 192             this.transferCohort = transferCohort;
 193         }
 194
 195         boolean isExpired(long timeout) {
 196             if (timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
 197                 transferCohort.abortTransfer();
 198                 return true;
 199             }
 200
 201             return false;
 202         }
 203     }
 204 }