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 static java.util.Objects.requireNonNull;
  11
  12 import akka.actor.ActorRef;
  13 import akka.actor.ActorSelection;
  14 import com.google.common.annotations.VisibleForTesting;
  15 import com.google.common.base.Stopwatch;
  16 import java.util.Optional;
  17 import java.util.concurrent.TimeUnit;
  18 import org.eclipse.jdt.annotation.NonNull;
  19 import org.eclipse.jdt.annotation.Nullable;
  20 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  21 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  22 import org.opendaylight.controller.cluster.raft.RaftActorLeadershipTransferCohort;
  23 import org.opendaylight.controller.cluster.raft.RaftState;
  24 import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
  25 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  26
  27 /**
  28  * The behavior of a RaftActor when it is in the Leader state.
  29  *
  30  * <p>
  31  * Leaders:
  32  * <ul>
  33  * <li> Upon election: send initial empty AppendEntries RPCs
  34  * (heartbeat) to each server; repeat during idle periods to
  35  * prevent election timeouts (§5.2)
  36  * <li> If command received from client: append entry to local log,
  37  * respond after entry applied to state machine (§5.3)
  38  * <li> If last log index ≥ nextIndex for a follower: send
  39  * AppendEntries RPC with log entries starting at nextIndex
  40  * <li> If successful: update nextIndex and matchIndex for
  41  * follower (§5.3)
  42  * <li> If AppendEntries fails because of log inconsistency:
  43  * decrement nextIndex and retry (§5.3)
  44  * <li> If there exists an N such that N &gt; commitIndex, a majority
  45  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  46  * set commitIndex = N (§5.3, §5.4).
  47  * </ul>
  48  */
  49 public class Leader extends AbstractLeader {
  50     /**
  51      * Internal message sent to periodically check if this leader has become isolated and should transition
  52      * to {@link IsolatedLeader}.
  53      */
  54     @VisibleForTesting
  55     static final Object ISOLATED_LEADER_CHECK = new Object();
  56
  57     private final Stopwatch isolatedLeaderCheck = Stopwatch.createStarted();
  58     private @Nullable LeadershipTransferContext leadershipTransferContext;
  59
  60     Leader(final RaftActorContext context, @Nullable final AbstractLeader initializeFromLeader) {
  61         super(context, RaftState.Leader, initializeFromLeader);
  62     }
  63
  64     public Leader(final RaftActorContext context) {
  65         this(context, null);
  66     }
  67
  68     @Override
  69     public RaftActorBehavior handleMessage(final ActorRef sender, final Object originalMessage) {
  70         requireNonNull(sender, "sender should not be null");
  71
  72         if (ISOLATED_LEADER_CHECK.equals(originalMessage)) {
  73             if (isLeaderIsolated()) {
  74                 log.warn("{}: At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
  75                     context.getId(), getMinIsolatedLeaderPeerCount(), getLeaderId());
  76                 return internalSwitchBehavior(new IsolatedLeader(context, this));
  77             } else {
  78                 return this;
  79             }
  80         } else {
  81             return super.handleMessage(sender, originalMessage);
  82         }
  83     }
  84
  85     @Override
  86     protected void beforeSendHeartbeat() {
  87         if (isolatedLeaderCheck.elapsed(TimeUnit.MILLISECONDS)
  88                 > context.getConfigParams().getIsolatedCheckIntervalInMillis()) {
  89             context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
  90             isolatedLeaderCheck.reset().start();
  91         }
  92
  93         if (leadershipTransferContext != null && leadershipTransferContext.isExpired(
  94                 context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
  95             log.debug("{}: Leadership transfer expired", logName());
  96             leadershipTransferContext = null;
  97         }
  98     }
  99
 100     @Override
 101     protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
 102             final AppendEntriesReply appendEntriesReply) {
 103         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
 104         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
 105         return returnBehavior;
 106     }
 107
 108     /**
 109      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
 110      * <ul>
 111      * <li>Start a timer (Stopwatch).</li>
 112      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
 113      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
 114      * <li>If it matches,
 115      *   <ul>
 116      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
 117      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
 118      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
 119      *   </ul></li>
 120      * <li>Otherwise if the election time out period elapses, notify
 121      *     {@link RaftActorLeadershipTransferCohort#abortTransfer}.</li>
 122      * </ul>
 123      *
 124      * @param leadershipTransferCohort the cohort participating in the leadership transfer
 125      */
 126     public void transferLeadership(@NonNull final RaftActorLeadershipTransferCohort leadershipTransferCohort) {
 127         log.debug("{}: Attempting to transfer leadership", logName());
 128
 129         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
 130
 131         // Send an immediate heart beat to the followers.
 132         sendAppendEntries(0, false);
 133     }
 134
 135     private void tryToCompleteLeadershipTransfer(final String followerId) {
 136         if (leadershipTransferContext == null) {
 137             return;
 138         }
 139
 140         final Optional<String> requestedFollowerIdOptional
 141                 = leadershipTransferContext.transferCohort.getRequestedFollowerId();
 142         if (requestedFollowerIdOptional.isPresent() && !requestedFollowerIdOptional.get().equals(followerId)) {
 143             // we want to transfer leadership to specific follower
 144             return;
 145         }
 146
 147         FollowerLogInformation followerInfo = getFollower(followerId);
 148         if (followerInfo == null) {
 149             return;
 150         }
 151
 152         long lastIndex = context.getReplicatedLog().lastIndex();
 153         boolean isVoting = context.getPeerInfo(followerId).isVoting();
 154
 155         log.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
 156                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
 157
 158         if (isVoting && followerInfo.getMatchIndex() == lastIndex) {
 159             log.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
 160
 161             // We can't be sure if the follower has applied all its log entries to its state so send an
 162             // additional AppendEntries with the latest commit index.
 163             sendAppendEntries(0, false);
 164
 165             // Now send a TimeoutNow message to the matching follower to immediately start an election.
 166             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 167             followerActor.tell(TimeoutNow.INSTANCE, context.getActor());
 168
 169             log.debug("{}: Leader transfer complete", logName());
 170
 171             leadershipTransferContext.transferCohort.transferComplete();
 172             leadershipTransferContext = null;
 173         }
 174     }
 175
 176     @Override
 177     public void close() {
 178         if (leadershipTransferContext != null) {
 179             LeadershipTransferContext localLeadershipTransferContext = leadershipTransferContext;
 180             leadershipTransferContext = null;
 181             localLeadershipTransferContext.transferCohort.abortTransfer();
 182         }
 183
 184         super.close();
 185     }
 186
 187     @VisibleForTesting
 188     void markFollowerActive(final String followerId) {
 189         getFollower(followerId).markFollowerActive();
 190     }
 191
 192     @VisibleForTesting
 193     void markFollowerInActive(final String followerId) {
 194         getFollower(followerId).markFollowerInActive();
 195     }
 196
 197     private static class LeadershipTransferContext {
 198         RaftActorLeadershipTransferCohort transferCohort;
 199         Stopwatch timer = Stopwatch.createStarted();
 200
 201         LeadershipTransferContext(final RaftActorLeadershipTransferCohort transferCohort) {
 202             this.transferCohort = transferCohort;
 203         }
 204
 205         boolean isExpired(final long timeout) {
 206             if (timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
 207                 transferCohort.abortTransfer();
 208                 return true;
 209             }
 210
 211             return false;
 212         }
 213     }
 214 }