Each group can elect its own leader. There can be only one leader at a time in a group. Only members that are running for the election can be elected. As soon as one of leader steps down or dies, a new member that was running for the election will be elected.
import time import uuid import six from tooz import coordination ALIVE_TIME = 1 coordinator = coordination.get_coordinator('zake://', b'host-1') coordinator.start() # Create a group group = six.binary_type(six.text_type(uuid.uuid4()).encode('ascii')) request = coordinator.create_group(group) request.get() # Join a group request = coordinator.join_group(group) request.get() def when_i_am_elected_leader(event): # event is a LeaderElected event print(event.group_id, event.member_id) # Propose to be a leader for the group coordinator.watch_elected_as_leader(group, when_i_am_elected_leader) start = time.time() while time.time() - start < ALIVE_TIME: coordinator.heartbeat() coordinator.run_watchers() time.sleep(0.1) coordinator.stop()
The method tooz.coordination.CoordinationDriver.watch_elected_as_leader() allows to register for a function to be called back when the member is elected as a leader. Using this function indicates that the run is therefore running for the election. The member can stop running by unregistering all its callbacks with tooz.coordination.CoordinationDriver.unwatch_elected_as_leader(). It can also temporarily try to step down as a leader with tooz.coordination.CoordinationDriver.stand_down_group_leader(). If another member is in the run for election, it may be elected instead.
To retrieve the leader of a group, even when not being part of the group, the method tooz.coordination.CoordinationDriver.get_leader() can be used.