Physical replication from x86_64 to ARM64

Fellow Postgres Admins and Developers,

With the arrival of ARM compute nodes on AWS and an existing fleet of
Postgres clusters running on x86_64 nodes the question arises how to
migrate existing Postgres clusters to ARM64 nodes, ideally with zero
downtime, as one is used to.

Initial experiments show no observable problems when copying PGDATA or in
fact using physical streaming replication between the two CPU
architectures. In our case Postgres is using Docker based on Ubuntu 18.04
base images and PGDG packages for Postgres 13. On top of that, we checked
existing indexes with the amcheck
<https://www.postgresql.org/docs/current/amcheck.html> extension, which did
not reveal any issues.

However experiments are not valid to exclude all corner cases, thus we are
curious to hear other input on that matter, as we believe this is of
relevance to a bigger audience and ARM is not unlikely to be available on
other non AWS platforms going forward.

It is our understanding that AWS RDS in fact for Postgres 12 and Postgres
13 allows the change from x86 nodes to ARM nodes on the fly, which gives us
some indication that if done right, both platforms are indeed compatible.

Looking forward to your input and discussion points!

--
Jan Mußler
Engineering Manager - Team Acid & Team Aruha | Zalando SE