RDS Replication Management
RDS provides an rds_replication role that is required for doing replication on RDS in postgres. This role does NOT have the REPLICATION priviledge required to muck with the WAL readers. So there must be some internal to RDS implementation that allows the replciation management. For instance, if you log into a postgres instance with a user with the rds_replication role you cannnot execute the pg_replication_slot_advance stored procedure to move the lsn for the slot around.
The master user provided by RDS does not even have this role or SUPERUSER to grant this role. They have rds_superuser which does not have the ability to grant REPLICATION.