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.Optional;
  16 import com.google.common.base.Stopwatch;
  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(RaftActorContext context, @Nullable AbstractLeader initializeFromLeader) {
  61         super(context, RaftState.Leader, initializeFromLeader);
  62     }
  63
  64     public Leader(RaftActorContext context) {
  65         this(context, null);
  66     }
  67
  68     @Override
  69     public RaftActorBehavior handleMessage(ActorRef sender, 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(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 102         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
 103         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
 104         return returnBehavior;
 105     }
 106
 107     /**
 108      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
 109      * <ul>
 110      * <li>Start a timer (Stopwatch).</li>
 111      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
 112      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
 113      * <li>If it matches,
 114      *   <ul>
 115      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
 116      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
 117      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
 118      *   </ul></li>
 119      * <li>Otherwise if the election time out period elapses, notify
 120      *     {@link RaftActorLeadershipTransferCohort#abortTransfer}.</li>
 121      * </ul>
 122      *
 123      * @param leadershipTransferCohort the cohort participating in the leadership transfer
 124      */
 125     public void transferLeadership(@NonNull RaftActorLeadershipTransferCohort leadershipTransferCohort) {
 126         log.debug("{}: Attempting to transfer leadership", logName());
 127
 128         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
 129
 130         // Send an immediate heart beat to the followers.
 131         sendAppendEntries(0, false);
 132     }
 133
 134     private void tryToCompleteLeadershipTransfer(String followerId) {
 135         if (leadershipTransferContext == null) {
 136             return;
 137         }
 138
 139         final Optional<String> requestedFollowerIdOptional
 140                 = leadershipTransferContext.transferCohort.getRequestedFollowerId();
 141         if (requestedFollowerIdOptional.isPresent() && !requestedFollowerIdOptional.get().equals(followerId)) {
 142             // we want to transfer leadership to specific follower
 143             return;
 144         }
 145
 146         FollowerLogInformation followerInfo = getFollower(followerId);
 147         if (followerInfo == null) {
 148             return;
 149         }
 150
 151         long lastIndex = context.getReplicatedLog().lastIndex();
 152         boolean isVoting = context.getPeerInfo(followerId).isVoting();
 153
 154         log.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
 155                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
 156
 157         if (isVoting && followerInfo.getMatchIndex() == lastIndex) {
 158             log.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
 159
 160             // We can't be sure if the follower has applied all its log entries to its state so send an
 161             // additional AppendEntries with the latest commit index.
 162             sendAppendEntries(0, false);
 163
 164             // Now send a TimeoutNow message to the matching follower to immediately start an election.
 165             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 166             followerActor.tell(TimeoutNow.INSTANCE, context.getActor());
 167
 168             log.debug("{}: Leader transfer complete", logName());
 169
 170             leadershipTransferContext.transferCohort.transferComplete();
 171             leadershipTransferContext = null;
 172         }
 173     }
 174
 175     @Override
 176     public void close() {
 177         if (leadershipTransferContext != null) {
 178             LeadershipTransferContext localLeadershipTransferContext = leadershipTransferContext;
 179             leadershipTransferContext = null;
 180             localLeadershipTransferContext.transferCohort.abortTransfer();
 181         }
 182
 183         super.close();
 184     }
 185
 186     @VisibleForTesting
 187     void markFollowerActive(String followerId) {
 188         getFollower(followerId).markFollowerActive();
 189     }
 190
 191     @VisibleForTesting
 192     void markFollowerInActive(String followerId) {
 193         getFollower(followerId).markFollowerInActive();
 194     }
 195
 196     private static class LeadershipTransferContext {
 197         RaftActorLeadershipTransferCohort transferCohort;
 198         Stopwatch timer = Stopwatch.createStarted();
 199
 200         LeadershipTransferContext(RaftActorLeadershipTransferCohort transferCohort) {
 201             this.transferCohort = transferCohort;
 202         }
 203
 204         boolean isExpired(long timeout) {
 205             if (timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
 206                 transferCohort.abortTransfer();
 207                 return true;
 208             }
 209
 210             return false;
 211         }
 212     }
 213 }