This diagram of automatic failover shows the following relationships:

Two failover controllers have lines pointing to the ZooKeeper. Each failover controller has a line pointing to a JobTracker on the same server (3 or 4). The JobTracker on server 3 is in active mode, and the JobTracker on server 4 is in hot standby mode.

The active JobTracker has lines pointing to the three TaskTrackers, and they have lines pointing to both JobTrackers.