UPDATE:
Currently, Red Hat Satellite using RDS doesn’t work for 2 reasons;
* For Red Hat Satellite 6.10, Postgresql 12.1 the only version of DB supported as an external DB
https://access.redhat.com/documentation/en-us/red_hat_satellite/6.10/html/installing_satellite_server_from_a_disconnected_network/performing-additional-configuration#postgresql-as-an-external-database-considerations_satellite

While I was trying to install oldest Postgresql available was 12.5.

• Require “rh-postgresql12-postgresql-evr” pkg
  Installation will fail saying ;
  rh-postgresql12-postgresql-evr pkg with a matching version with the RDS, which doesn’t exist.

• Subnet group – to make sure it would have the same subnet with the Satellite “web”.
  
• Adding inbound address to a default Security Group
  
• Using “pgsql” client to create various users as it is stated in;
  https://access.redhat.com/documentation/en-us/red_hat_satellite/6.10/html-single/installing_satellite_server_from_a_connected_network/index#installing-postgresql_satellite
  
  
• Grant each users roles to “postgres” user

postgres=> GRANT foreman to postgres;
GRANT ROLE
postgres=> GRANT candlepin to postgres;
GRANT ROLE
postgres=> GRANT pulp to postgres;
GRANT ROLE

• Create databases