[andruby]

PG's internal wal-level replication? primary to a read-replica, and then switch the read to become the primary. You'll have a bit of downtime while you stop connections on the original server, switch the new server to primary, and update your app config to connect to the new server.

I believe that's a pretty standard way to provide "HA" postgres. (We use Patroni for our HA setup)

https://github.com/patroni/patroni

[dikei]

We use the same setup, though we use PGBouncer so after switching primary we just force reconnect all clients from PGBouncer instead.

The clients will have to retry on-going transactions, but that's a basic fault tolerant requirement anyway.