58cf7161062c1eb67568930fb15252aadd21a23e
[controller.git] / 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  * <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 = Stopwatch.createStarted();
56     private @Nullable 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(RaftState.IsolatedLeader);
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) > context.getConfigParams().getIsolatedCheckIntervalInMillis()){
86             context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
87             isolatedLeaderCheck.reset().start();
88         }
89
90         if(leadershipTransferContext != null && leadershipTransferContext.isExpired(
91                 context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
92             LOG.debug("{}: Leadership transfer expired", logName());
93             leadershipTransferContext = null;
94         }
95     }
96
97     @Override
98     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
99         RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
100         tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
101         return returnBehavior;
102     }
103
104     /**
105      * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
106      * <ul>
107      * <li>Start a timer (Stopwatch).</li>
108      * <li>Send an initial AppendEntries heartbeat to all followers.</li>
109      * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
110      * <li>If it matches, </li>
111      *   <ul>
112      *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
113      *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
114      *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
115      *   </ul>
116      * <li>Otherwise if the election time out period elapses, notify
117      *     {@link RaftActorLeadershipTransferCohort#abortTtransfer}.</li>
118      * </ul>
119      *
120      * @param leadershipTransferCohort
121      */
122     public void transferLeadership(@Nonnull RaftActorLeadershipTransferCohort leadershipTransferCohort) {
123         LOG.debug("{}: Attempting to transfer leadership", logName());
124
125         leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
126
127         // Send an immediate heart beat to the followers.
128         sendAppendEntries(0, false);
129     }
130
131     private void tryToCompleteLeadershipTransfer(String followerId) {
132         if(leadershipTransferContext == null) {
133             return;
134         }
135
136         FollowerLogInformation followerInfo = getFollower(followerId);
137         if(followerInfo == null) {
138             return;
139         }
140
141         long lastIndex = context.getReplicatedLog().lastIndex();
142         boolean isVoting = context.getPeerInfo(followerId).isVoting();
143
144         LOG.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
145                 logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
146
147         if(isVoting && followerInfo.getMatchIndex() == lastIndex) {
148             LOG.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
149
150             // We can't be sure if the follower has applied all its log entries to its state so send an
151             // additional AppendEntries with the latest commit index.
152             sendAppendEntries(0, false);
153
154             // Now send a TimeoutNow message to the matching follower to immediately start an election.
155             ActorSelection followerActor = context.getPeerActorSelection(followerId);
156             followerActor.tell(TimeoutNow.INSTANCE, context.getActor());
157
158             LOG.debug("{}: Leader transfer complete", logName());
159
160             leadershipTransferContext.transferCohort.transferComplete();
161             leadershipTransferContext = null;
162         }
163     }
164
165     @Override
166     public void close() {
167         if(leadershipTransferContext != null) {
168             LeadershipTransferContext localLeadershipTransferContext = leadershipTransferContext;
169             leadershipTransferContext = null;
170             localLeadershipTransferContext.transferCohort.abortTransfer();
171         }
172
173         super.close();
174     }
175
176     @VisibleForTesting
177     void markFollowerActive(String followerId) {
178         getFollower(followerId).markFollowerActive();
179     }
180
181     @VisibleForTesting
182     void markFollowerInActive(String followerId) {
183         getFollower(followerId).markFollowerInActive();
184     }
185
186     private static class LeadershipTransferContext {
187         RaftActorLeadershipTransferCohort transferCohort;
188         Stopwatch timer = Stopwatch.createStarted();
189
190         LeadershipTransferContext(RaftActorLeadershipTransferCohort transferCohort) {
191             this.transferCohort = transferCohort;
192         }
193
194         boolean isExpired(long timeout) {
195             if(timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
196                 transferCohort.abortTransfer();
197                 return true;
198             }
199
200             return false;
201         }
202     }
203 }

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