To check if you need to delete ZK Failover Controllers, on the Ambari Server host:

curl -u <AMBARI_USER>:<AMBARI_PW> -H "X-Requested-By: ambari" -i <AMBARI_PROTO>://localhost:<AMBARI_PORT>/api/v1/clusters/<CLUSTER_NAME>/host_components?HostRoles/component_name=ZKFC

If this returns an empty items array, you may proceed to Modify HDFS Configuration. Otherwise you must use the following DELETE commands:

To delete all ZK Failover Controllers, on the Ambari Server host:

curl -u <AMBARI_USER>:<AMBARI_PW> -H "X-Requested-By: ambari" -i -X DELETE <AMBARI_PROTO>://localhost:<AMBARI_PORT>/api/v1/clusters/<CLUSTER_NAME>/hosts/<NAMENODE_HOSTNAME>/host_components/ZKFC curl -u <AMBARI_USER>:<AMBARI_PW> -H "X-Requested-By: ambari" -i -X DELETE <AMBARI_PROTO>://localhost:<AMBARI_PORT>/api/v1/clusters/<CLUSTER_NAME>/hosts/<ADDITIONAL_NAMENODE_HOSTNAME>/host_components/ZKFC

Verify that the ZK Failover Controllers have been deleted. On the Ambari Server host:

curl -u <AMBARI_USER>:<AMBARI_PW> -H "X-Requested-By: ambari" -i <AMBARI_PROTO>://localhost:<AMBARI_PORT>/api/v1/clusters/<CLUSTER_NAME>/host_components?HostRoles/component_name=ZKFC

This command should return an empty items array.