/*
* Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.cluster;
import com.hazelcast.core.Cluster;
import com.hazelcast.instance.NodeState;
import com.hazelcast.spi.impl.AllowedDuringPassiveState;
/**
* {@code ClusterState} consists several states of the cluster
* which each state can allow and/or deny specific actions
* and/or change behaviours of specific actions.
* <p/>
* There are 5 states:
* <ol>
* <li>
* {@link #ACTIVE}:
* Cluster will continue to operate without any restriction.
* </li>
* <li>
* {@link #NO_MIGRATION}:
* Migrations (partition rebalancing) and backup replications
* are not allowed. Cluster will continue to operate without any restriction.
* </li>
* <li>
* {@link #FROZEN}:
* New members are not allowed to join, partition table/assignments will be frozen.
* All other operations are allowed and will operate without any restriction.
* If some members leave the cluster during it is in {@code FROZEN} state, they can join back.
* </li>
* <li>
* {@link #PASSIVE}:
* New members are not allowed to join.
* All operations, except the ones marked with {@link AllowedDuringPassiveState},
* will be rejected immediately.
* </li>
* <li>
* {@link #IN_TRANSITION}:
* Shows that {@code ClusterState} is in transition.
* This is a temporary & intermediate state, not allowed to set explicitly.
* </li>
* </ol>
* <p/>
* By default, cluster will be in {@code ACTIVE} state. During split-brain merge process,
* state of the cluster, that is going to join to the major side,
* will be changed to {@code FROZEN} automatically before merge
* and will be set to the state of the new cluster after merge.
*
* @see Cluster#getClusterState()
* @see Cluster#changeClusterState(ClusterState)
* @see NodeState
* @since 3.6
*/
public enum ClusterState {
/**
* In {@code ACTIVE} state, cluster will continue to operate without any restriction.
* All operations are allowed. This is default state of a cluster.
*/
ACTIVE(true, true),
/**
* In {@code NO_MIGRATION} state of the cluster, migrations (partition rebalancing) and backup replications
* are not allowed.
* <ul>
* <li>
* When a new member joins, it will not be assigned any partitions until cluster state changes to {@link ClusterState#ACTIVE}.
* </li>
* <li>
* When a member leaves, backups of primary replicas owned by that member will be promoted to primary.
* But missing backup replicas will not be created/replicated until cluster state changes to {@link ClusterState#ACTIVE}.
* </li>
* </ul>
*
* Cluster will continue to operate without any restriction. All operations are allowed.
*
* @since 3.9
*/
NO_MIGRATION(true, false),
/**
* In {@code FROZEN} state of the cluster:
* <ul>
* <li>
* New members are not allowed to join, except the members left during {@code FROZEN} or {@link ClusterState#PASSIVE} state.
* For example, cluster has 3 nodes; A, B and C in {@code FROZEN} state. If member B leaves
* the cluster (either proper shutdown or crash), it will be allowed to re-join to the cluster.
* But another member D, won't be able to join.
* </li>
* <li>
* Partition table/assignments will be frozen. When a member leaves the cluster, its partition
* assignments (as primary and backup) will remain the same, until either that member re-joins
* to the cluster or {@code ClusterState} changes back to {@code ACTIVE}.
* If that member re-joins in {@code FROZEN}, it will own all previous partition assignments as it is.
* If {@code ClusterState} changes to {@code ACTIVE} then partition re-balancing process will
* kick-in and all unassigned partitions will be assigned to active members.
* It's not allowed to change {@code ClusterState} to {@code FROZEN}
* when there are pending migration/replication tasks in the system.
* </li>
* <li>
* Nodes continue to stay in {@link NodeState#ACTIVE} state when cluster goes into the {@code FROZEN} state.
* </li>
* <li>
* All other operations except migrations are allowed and will operate without any restriction.
* </li>
* </ul>
*/
FROZEN(false, false),
/**
* In {@code PASSIVE} state of the cluster:
* <ul>
* <li>
* New members are not allowed to join, except the members left during {@link ClusterState#FROZEN} or {@code PASSIVE} state.
* </li>
* * <li>
* Partition table/assignments will be frozen. It's not allowed to change {@code ClusterState}
* to {@code PASSIVE} when there are pending migration/replication tasks in the system. If some
* nodes leave the cluster while cluster is in {@code PASSIVE} state, they will be removed from the
* partition table if cluster state moves back to {@link #ACTIVE}.
* </li>
* <li>
* When cluster state is moved to {@code PASSIVE}, node are moved to {@link NodeState#PASSIVE}.
* In this regard, when cluster state moves to another state from {@code PASSIVE}, nodes become
* {@link NodeState#ACTIVE}.
* </li>
* <li>
* All operations, except the ones marked with {@link AllowedDuringPassiveState},
* will be rejected immediately.
* </li>
* </ul>
*/
PASSIVE(false, false),
/**
* Shows that ClusterState is in transition. When a state change transaction is started,
* ClusterState will be shown as {@code IN_TRANSITION} during the transaction lifecycle.
* After transaction completes, it will be in either new state or its previous state
* depending on transaction's result.
* <p/>
* This is a temporary & intermediate state, not allowed to set explicitly.
* <p/>
* <ul>
* <li>
* Similar to the {@code FROZEN} state, new members are not allowed
* and migration/replication process will be paused.
* </li>
* <li>
* If membership change occurs in the cluster, cluster state transition will fail
* and will be reverted back to the previous state.
* </li>
* </ul>
*/
IN_TRANSITION(false, false);
private final boolean joinAllowed;
private final boolean migrationAllowed;
ClusterState(boolean joinAllowed, boolean migrationAllowed) {
this.joinAllowed = joinAllowed;
this.migrationAllowed = migrationAllowed;
}
/**
* Shows whether new member join is allowed.
* @return true when join is allowed, false otherwise
*/
public boolean isJoinAllowed() {
return joinAllowed;
}
/**
* Shows whether migrations and replications are allowed.
* @return true when migrations and replications are allowed, false otherwise
*/
public boolean isMigrationAllowed() {
return migrationAllowed;
}
}