[T-Winsnes]

We're going through this right now with hava.io

AWS RDS postgress 11.13 > 15.5

We ended up going with a relatively straight forward approach of unidirectional replication using pglogical. We have some experience doing the same migration from Google Cloud sql to AWS rds with zero downtime as well, which made us pretty confident that this will work and not impact customers in any visible way.

pglogical makes it relatively straight forwards to do this kind of migration. It's not always fast, but if you're happy with waiting for a few days while it gradually replicates the full database across to the new instances.

For us it gave us a bit more freedom in changing the storage type and size which was more difficult to do with some of the alternative approaches. We had oversized our storage to get more iops, so we wanted to change storage type as well as reducing the size of the storage, which meant we couldn't do the simple restore from a snapshot.