Followup from How To Create New Standby Using Active Standby Duplication From Existing Standby
There are too many contents to post to blog.
Note: 12c = 12.1 and 12.2
Access 12c Dataguard Multiple Standby Databases Switchover Using DGMGRL for more details.
Thanks to CrossMyP4th on Twitter about Password file not syncing between primary and standby. As of 12.2, this is automatic.
What can happen when password files are not in sync: 12.1.0.2.0 ORA-01033: ORACLE initialization or shutdown in progress cascade standby
A useful enhancement in 12cR2 is that password files are automatically synchronized in a Data Guard environment: Auto Sync for Password Files in #Oracle 12.2 Data Guard