[aeyes]

Except that there is no way to upgrade a Postgres instance on RDS with a planned 15 minute downtime. You can't control when the reboots happen, you start the process and the cutover might kick in an hour later, two hours later, three hours later - you don't know when the reboots are going to happen and you can't control it.

If you have replicas they'll upgrade in parallel and will reboot at random times for even more fun.

So unless you can afford random unavailability in a timeframe which can last several hours (depending on DB size) the logical replication approach is the only way to do upgrades on RDS.

The bigger the instance, the harder the problem.