Is there a reason why repmgr cannot automatically fence the old primary postgres server after the standby has been promoted?
In my current setup, if it's not a network failure, I use a custom script to promote the standby server to be the primary server, then ssh over the old primary server and disable Postgres by renaming the postgres.conf file. This does not guard against all scenerio.
What would be nice is if repmgr could check its own state tables (cluster show) and if it sees that a standby has been promoted, then repmgr on the old primary should automatically disable postgres. This should be possible once the network is restored, for example, and it notices that there's a new primary server.