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Managing Cluster States

With the release of 3.6, Hazelcast introduces two new operations to manage the states of your cluster. These operations can be performed using the new methods changeClusterState() and shutdown() which are in the Cluster interface.

By changing the state of your cluster, you can allow/restrict several cluster operations or change the behavior of those operations. Hazelcast clusters have the following states:

  • ACTIVE: This is the default cluster state. Cluster continues to operate without restrictions.

  • FROZEN:
    • In this state, the partition table is frozen and partition assignments are not performed.
    • Your cluster does not accept new members.
    • If a member leaves, it can join back. Its partition assignments (both primary and replica) remain the same until either it joins back or the cluster state is changed to ACTIVE. When it joins back to the cluster, it will own all previous partition assignments as it was. On the other hand, when the cluster state changes to ACTIVE, re-partitioning starts and unassigned partitions are assigned to the active members.
    • All other operations in the cluster, except migration, continue without restrictions.
    • You cannot change the state of a cluster to FROZEN when migration/replication tasks are being performed.

  • PASSIVE:
    • In this state, the partition table is frozen and partition assignments are not performed.
    • Your cluster does not accept new members.
    • If a member leaves while the cluster is in this state, the member will be removed from the partition table if cluster state moves back to ACTIVE.
    • This state rejects ALL operations immediately EXCEPT the read-only operations like map.get() and cache.get(), replication and cluster heartbeat tasks.
    • You cannot change the state of a cluster to PASSIVE when migration/replication tasks are being performed.

  • IN_TRANSITION:
    • This state shows that the state of the cluster is in transition.
    • You cannot set your cluster's state as IN_TRANSITION explicitly.
    • It is a temporary and intermediate state.
    • During this state, your cluster does not accept new members and migration/replication tasks are paused.

image NOTE: All in-cluster methods are fail-fast, i.e. when a method fails in the cluster, it throws an exception immediately (it will not be retried).

The following snippet is from the Cluster interface showing the new methods used to manage your cluster's states.

public interface Cluster {
...
...
    ClusterState getClusterState();
    void changeClusterState(ClusterState newState);
    void changeClusterState(ClusterState newState, TransactionOptions transactionOptions);
    void shutdown();
    void shutdown(TransactionOptions transactionOptions);

Please refer to the Cluster interface for information on these methods.