I'm orchestrating Postgres to behave as a leader-follower cluster. I've run into issues when I am scaling down a connection count for a cluster (scaling up is fine -- scaling down results in fatal errors). I use an open source tool I've written to orchestrate the cluster called Governor (http://github.com/compose/governor). It would work if I weren't running hot_standby, but alas…I'm running with it.
I found the code which throws the fatal is actually a pre-flight test for hot_standby written in 2009 (i.e. battle tested):
In researching these lines of code, it appears the original FATAL code was put in place to ensure that a hot_standby is as close as possibly configured the same as the leader.
This change will also allow backups taken using `pg_basebackup` to work with settings that different from the original host.
