As you can see the AWS FAQ mentions that we can create only one database per instance for Oracle.
1"RDS for Oracle: 1 database per instance; no limit on number of schemas per database imposed by software". What exactly is your question?– TimFeb 15, 2018 at 3:43
I want to use same RDS for multiple configuration of same software, If i simply create different user it tries to populate data which is already populated.so my thought is If I able to multiple instances which is possible in oracle 11g using DBCA. Can we do same on RDS instead of creating multiple instances which will affect my cost.– Mahesh WaghFeb 15, 2018 at 6:07
The "database" component of an Oracle database installation got complicated.
Before 12c came about, the 'database' part essentially referred to the datafiles, including those for the database metadata. An 'instance' was essentially processes and memory, and an instance could only work with one database at a time. You could have multiple instances working on one database with shared storage (Oracle RAC). With a physical server, you could run multiple databases but each would have their own instance but that generally wasn't recommended.
In 12c, Oracle began a separation into a 'Container Database' that could manage one or more 'Pluggable Database'. You would still have one (or more) instances opening a container database, but there could be multiple pluggable database within that container. Then you'd only have one instance on a server, running one or more pluggable databases.
The 'multiple pluggable databases' is the bit that RDS doesn't support. "It is important to note that to get this same feature on Amazon you can not use RDS because they prohibit you from using this option. "
As of 19c AWS support pluggable databases on Oracle RDS. See aws.amazon.com/about-aws/whats-new/2021/05/… Aug 31, 2021 at 7:37
1docs.aws.amazon.com/AmazonRDS/latest/UserGuide/… "Currently, RDS for Oracle supports a subset of multitenant architecture called the single-tenant architecture. In this case, your CDB contains only one PDB. "– GarySep 6, 2021 at 6:09