Amazon RDS Oracle XStream support for CDB Database

You've identified a key limitation with using XStream in RDS for Oracle CDB environments. When using RDS for Oracle with the multitenant architecture (CDB), you cannot connect to the root container (CDB$ROOT) level. Amazon RDS restricts access to the CDB and only allows connections to the tenant databases (PDBs).

This restriction presents a challenge for implementing XStream, as the CREATE_OUTBOUND procedure needs to be executed at the CDB$ROOT level in Oracle 19c/21c CDB databases.

Unfortunately, there isn't a direct workaround for this limitation within standard RDS for Oracle. You cannot connect to the container and create users or execute commands at that level, as connections are limited to the PDB level only.

If you require direct access to the CDB level to configure XStream components, you might want to consider Amazon RDS Custom for Oracle instead. RDS Custom provides access to built-in Oracle users like SYS and SYSTEM and grants more administrative privileges, which would allow you to execute the necessary commands at the CDB$ROOT level.

Alternatively, if you need to stay with standard RDS, you may need to continue using non-CDB architecture for your Oracle databases that require XStream functionality, at least until Amazon introduces support for this specific use case.
Sources
Can I connect to Oracle RDS root container | AWS re:Post
About RDS's oracle cdb issue | AWS re:Post