org.apache.flink.runtime.leaderelection

Interface LeaderElectionService

All Known Implementing Classes:

DefaultLeaderElectionService, StandaloneLeaderElectionService

public interface LeaderElectionService

Interface for a service which allows to elect a leader among a group of contenders.

Prior to using this service, it has to be started calling the start method. The start method takes the contender as a parameter. If there are multiple contenders, then each contender has to instantiate its own leader election service.

Once a contender has been granted leadership he has to confirm the received leader session ID by calling the method confirmLeadership(UUID, String). This will notify the leader election service, that the contender has accepted the leadership specified and that the leader session id as well as the leader address can now be published for leader retrieval services.

Method Summary

Modifier and Type	Method and Description
void	confirmLeadership(UUID leaderSessionID, String leaderAddress) Confirms that the LeaderContender has accepted the leadership identified by the given leader session id.
boolean	hasLeadership(UUID leaderSessionId) Returns true if the LeaderContender with which the service has been started owns currently the leadership under the given leader session id.
void	start(LeaderContender contender) Starts the leader election service.
void	stop() Stops the leader election service.

Method Detail

start

void start(LeaderContender contender)
    throws Exception

Starts the leader election service. This method can only be called once.

Parameters:

contender - LeaderContender which applies for the leadership

Throws:

Exception

stop

void stop()
   throws Exception

Stops the leader election service.

Throws:

Exception

confirmLeadership

void confirmLeadership(UUID leaderSessionID,
                       String leaderAddress)

Confirms that the LeaderContender has accepted the leadership identified by the given leader session id. It also publishes the leader address under which the leader is reachable.

The rational behind this method is to establish an order between setting the new leader session ID in the LeaderContender and publishing the new leader session ID as well as the leader address to the leader retrieval services.

Parameters:

leaderSessionID - The new leader session ID

leaderAddress - The address of the new leader

hasLeadership

boolean hasLeadership(@Nonnull
                      UUID leaderSessionId)

Returns true if the LeaderContender with which the service has been started owns currently the leadership under the given leader session id.

Parameters:

leaderSessionId - identifying the current leader

Returns:

true if the associated LeaderContender is the leader, otherwise false