you can use pg_basebackup to kickstart a replication slave. You can then just just down old and use new with ~1sec downtime. If you need to upgrade postgres at

you can use pg_basebackup to kickstart a replication slave. You can then just just down old and use new with ~1sec downtime. If you need to upgrade postgres at same time, you can then cascade to another one slave on same "new" host for safety, and pg_upgrade on that one. This will result in a bit more downtime, but also upgrading postgres version.