software.amazon.kinesis.leader

Class DynamoDBLockBasedLeaderDecider

java.lang.Object

software.amazon.kinesis.leader.DynamoDBLockBasedLeaderDecider

All Implemented Interfaces:

LeaderDecider

public class DynamoDBLockBasedLeaderDecider
extends Object
implements LeaderDecider

Implementation for LeaderDecider to elect leader using lock on dynamo db table. This class uses AmazonDynamoDBLockClient library to perform the leader election.

The lock client is obtained from CoordinatorStateDAO.getDDBLockClient() on each isLeader() call, which routes to the appropriate table based on the current TableMigrationStatus. When migration completes (PENDING → COMPLETE), the DAO transparently switches from the legacy table lock client to the lease table lock client.

Field Summary

Fields inherited from interface software.amazon.kinesis.coordinator.LeaderDecider

METRIC_OPERATION_LEADER_DECIDER, METRIC_OPERATION_LEADER_DECIDER_IS_LEADER

Constructor Summary

Constructors

Constructor and Description
DynamoDBLockBasedLeaderDecider()

Method Summary

Modifier and Type	Method and Description
static DynamoDBLockBasedLeaderDecider	create(CoordinatorStateDAO coordinatorStateDao, String workerId, MetricsFactory metricsFactory, long leaseDurationInMillis, long heartbeatPeriodInMillis, TableMigrationStateMachine tableMigrationStateMachine)
void	initialize() Performs initialization tasks for decider if any.
Boolean	isLeader(String workerId) Check the lockItem in storage and if the current worker is not leader worker, then tries to acquire lock and returns true if it was able to acquire lock else false.
void	releaseLeadershipIfHeld() If the current worker is the leader, then releases the leadership else does nothing.
void	shutdown() Shuts down the leader decider, releasing any held lock and closing all lock clients.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DynamoDBLockBasedLeaderDecider

public DynamoDBLockBasedLeaderDecider()

Method Detail

create

public static DynamoDBLockBasedLeaderDecider create(CoordinatorStateDAO coordinatorStateDao,
                                                    String workerId,
                                                    MetricsFactory metricsFactory,
                                                    long leaseDurationInMillis,
                                                    long heartbeatPeriodInMillis,
                                                    TableMigrationStateMachine tableMigrationStateMachine)

initialize

public void initialize()

Description copied from interface: LeaderDecider

Performs initialization tasks for decider if any.

Specified by:

initialize in interface LeaderDecider

isLeader

public Boolean isLeader(String workerId)

Check the lockItem in storage and if the current worker is not leader worker, then tries to acquire lock and returns true if it was able to acquire lock else false.

Specified by:

isLeader in interface LeaderDecider

Parameters:

workerId - ID of the worker

Returns:

true if current worker is leader else false.

shutdown

public void shutdown()

Shuts down the leader decider, releasing any held lock and closing all lock clients.

This method releases the leadership lock if held and then closes the underlying DynamoDB lock clients (both legacy and lease table) via the DAO to stop their background heartbeat threads. This ensures that no locks are kept alive after shutdown.

Specified by:

shutdown in interface LeaderDecider

releaseLeadershipIfHeld

public void releaseLeadershipIfHeld()

Description copied from interface: LeaderDecider

If the current worker is the leader, then releases the leadership else does nothing. This might not be relevant for some implementations, for e.g. DeterministicShuffleShardSyncLeaderDecider does not have mechanism to release leadership. Current worker if leader releases leadership, it's possible that the current worker assume leadership sometime later again in future elections.

Specified by:

releaseLeadershipIfHeld in interface LeaderDecider