Understanding the rds_superuser role

In PostgreSQL, a role can define a user, a group, or a set of specific permissions granted to a group or user for various objects in the database. PostgreSQL commands to CREATE USER and CREATE GROUP have been replaced by the more general, CREATE ROLE with specific properties to distinguish database users. A database user can be thought of as a role with the LOGIN privilege.

Note

The CREATE USER and CREATE GROUP commands can still be used. For more information, see Database Roles in the PostgreSQL documentation.

The postgres user is the most highly privileged database user on your RDS for PostgreSQL DB instance. It has the characteristics defined by the following CREATE ROLE statement.

CREATE ROLE postgres WITH LOGIN NOSUPERUSER INHERIT CREATEDB CREATEROLE NOREPLICATION VALID UNTIL 'infinity'

The properties NOSUPERUSER, NOREPLICATION, INHERIT, and VALID UNTIL 'infinity' are the default options for CREATE ROLE, unless otherwise specified.

By default, postgres has privileges granted to the rds_superuser role, and permissions to create roles and databases. The rds_superuser role allows the postgres user to do the following:

• Add extensions that are available for use with Amazon RDS. For more information, see Working with PostgreSQL features supported by Amazon RDS for PostgreSQL

• Create roles for users and grant privileges to users. For more information, see CREATE ROLE and GRANT in the PostgreSQL documentation.

• Create databases. For more information, see CREATE DATABASE in the PostgreSQL documentation.

• Grant rds_superuser privileges to user roles that don't have these privileges, and revoke privileges as needed. We recommend that you grant this role only to those users who perform superuser tasks. In other words, you can grant this role to database administrators (DBAs) or system administrators.

• Grant (and revoke) the rds_replication role to database users that don't have the rds_superuser role.

• Grant (and revoke) the rds_password role to database users that don't have the rds_superuser role.

• Obtain status information about all database connections by using the pg_stat_activity view. When needed, rds_superuser can stop any connections by using pg_terminate_backend or pg_cancel_backend.

In the CREATE ROLE postgres... statement, you can see that the postgres user role specifically disallows PostgreSQL superuser permissions. RDS for PostgreSQL is a managed service, so you can't access the host OS, and you can't connect using the PostgreSQL superuser account. Many of the tasks that require superuser access on a stand-alone PostgreSQL are managed automatically by Amazon RDS.

For more information about granting privileges, see GRANT in the PostgreSQL documentation.

The rds_superuser role is one of several predefined roles in an RDS for PostgreSQL DB instance.

Note

In PostgreSQL 13 and earlier releases, predefined roles are known as default roles.

In the following list, you find some of the other predefined roles that are created automatically for a new RDS for PostgreSQL DB instance. Predefined roles and their privileges can't be changed. You can't drop, rename, or modify privileges for these predefined roles. Attempting to do so results in an error.

• rds_password – A role that can change passwords and set up password constraints for database users. The rds_superuser role is granted with this role by default, and can grant the role to database users. For more information, see Controlling user access to the PostgreSQL database.

  • For RDS for PostgreSQL versions older than 14, rds_password role can change passwords and set up password constraints for database users and users with rds_superuser role. From RDS for PostgreSQL version 14 and later, rds_password role can change passwords and set up password constraints only for database users. Only users with rds_superuser role can perform these actions on other users with rds_superuser role.

• rdsadmin – A role that's created to handle many of the management tasks that the administrator with superuser privileges would perform on a standalone PostgreSQL database. This role is used internally by RDS for PostgreSQL for many management tasks.

• rdstopmgr – A role that's used internally by Amazon RDS to support Multi-AZ deployments.

To see all predefined roles, you can connect to your RDS for PostgreSQL DB instance and use the psql \du metacommand. The output looks as follows:

List of roles
  Role name   |      Attributes                   |      Member of      
--------------+-----------------------------------+------------------------------------
postgres      | Create role, Create DB           +| {rds_superuser}
              | Password valid until infinity     |
rds_superuser | Cannot login                      | {pg_monitor,pg_signal_backend,
              |                                  +|   rds_replication,rds_password}
...

In the output, you can see that rds_superuser isn't a database user role (it can't login), but it has the privileges of many other roles. You can also see that database user postgres is a member of the rds_superuser role. As mentioned previously, postgres is the default value in the Amazon RDS console's Create database page. If you chose another name, that name is shown in the list of roles instead.