This jira is for a ZK-based FailoverController daemon. The FailoverController is a separate daemon from the NN that does the following:
- Initiates leader election (via ZK) when necessary
- Performs health monitoring (aka failure detection)
- Performs fail-over (standby to active and active to standby transitions)
- Heartbeats to ensure the liveness
It should have the same/similar interface as the Linux HA RM to aid pluggability.