Major Description
It is currently possible for users to make a standby NameNode failover to itself and become active. We shouldn't allow this to happen in case operators mistype and miss the fact that there are now two active NNs.
bash-4.1$ hdfs haadmin -ns ha-nn-uri -failover nn2 nn2 Failover from nn2 to nn2 successful
After the failover above, nn2 will be active.