Always is a trivial implementation that asserts the current instance to always be the leader (or not).

NewPoller returns a detector implementation given the poll interval and function that polls.

Leader means the current node / instance is a leader.

NotLeader means the current node is not a leader.

Unknown indicates some exception happened while determining leadership.

Leadership is a struct that captures the leadership state, possibly error if exception occurs.

Detector is the interface for determining whether this instance is a leader.

CheckLeaderFunc is all that a special backend needs to implement.

Status indicates leadership status.