Create DB Control in Active/Passive High Availability Environments H/A

Before create DB Control, if environment variable ORACLE_HOSTNAME is not exported. The default DB Control Agent Name would be DBConsole__SID.

Since it is using actual hostname, this will cause DB control can't work upon failover.

The idea way is using virtual name.
Should you forget this , you can try to re-create DB control on both node, prior to create database or run dbua
i.e
export ORACLE_HOSTNAME=
emca -config dbcontrol db -repos recreate