BUG 2185 : Introduce RaftPolicy & DefaultRaftPolicy

[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / policy / RaftPolicy.java

diff --git a/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/policy/RaftPolicy.java b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/policy/RaftPolicy.java
new file mode 100644 (file)
index 0000000..a66caa4
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+++ b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/policy/RaftPolicy.java
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2015 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+
+package org.opendaylight.controller.cluster.raft.policy;
+
+/**
+ * The RaftPolicy is intended to change the default behavior of Raft. For example
+ * we may want to be able to determine which Raft replica should become the leader - with Raft elections are
+ * randomized so it is not possible to specify which replica should be the leader. The ability to specify
+ * the leader would be quite useful when testing a raft cluster.
+ *
+ * Similarly we may want to customize when exactly we apply a modification to the state - with Raft a modification
+ * is only applied to the state when the modification is replicated to a majority of the replicas. The ability to
+ * apply a modification to the state before consensus would be useful in scenarios where you have only 2 nodes
+ * in a Raft cluster and one of them is down but you still want the RaftActor to apply a modification to the state.
+ *
+ */
+public interface RaftPolicy {
+    /**
+     * According to Raft a Follower which does not receive a heartbeat (aka AppendEntries) in a given period should
+     * become a Candidate and trigger an election.
+     *
+     * @return true to enable automatic Raft elections, false to disable them
+     */
+    boolean automaticElectionsEnabled();
+
+    /**
+     * According to Raft consensus on a Raft entry is achieved only after a Leader replicates a log entry to a
+     * majority of it's followers
+     *
+     * @return true if modification should be applied before consensus, false to apply modification to state
+     * as per Raft
+     */
+    boolean applyModificationToStateBeforeConsensus();
+}