This JIRA is for the Common (generic) portion of HDFS-2185. It can't run on its own, but this JIRA will include unit tests using mock/dummy services.
Improve ActiveStandbyElector's behavior when session expires
HA: HDFS portion of ZK-based FailoverController
Automatic failover support for NN HA
Edge case split-brain race in ZK-based auto-failover
Security support for ZK Failover controller