Thanks @binduak,
I managed to make progress yesterday after looking at /etc/bahmni-backrest.conf contents. I see that documented in the wiki you mentioned, but I missed earlier. I got the backup/restore working, but I felt it is unnecessarily complicated. In general people don’t like to take partial backup. When things go wrong, they want their system to revert back to a previous stable checkpoint. So it is better to have one file that contains all the required data, instead of spreading it across many files. Customizations should be optional, and not difficult as backup file is understood by backup/restore commands. If there is any more work planned in this area, I am interested in contributing.