We have Postgres master-slave replication without Docker containers (standalone). In a near future we will shutdown master forever and the slave will become master. But we would like to have Postgres to work in Docker, because other several services will run in Docker too. The main point I am worried to is possible different Linux users in Postgres in Docker and standalone Postgres. For the latter it is postgres right now.
I understand the meaning of PGDATA and others environment variables of Postgres in Docker. But don't know how to deal with users/groups for my case.