RDS SQL Licenses

As per Quotas and constraints for Amazon RDS

The following limitations apply to the Amazon RDS DB instances:

- 10 for each SQL Server edition (Enterprise, Standard, Web, and Express) under the "license-included" model

If your application requires more DB instances, you can request additional DB instances by opening the Service Quotas console. In the navigation pane, choose AWS services. Choose Amazon Relational Database Service (Amazon RDS), choose a quota, and follow the directions to request a quota increase. For more information, see Requesting a quota increase in the Service Quotas User Guide.

Yes, the limitation you're encountering is related to a specific quota for RDS instances with the "license-included" option. These quotas are typically hard limits, but they can often be adjusted based on your specific needs.

For Oracle RDS instances with the "license-included" option, there is a documented limit of 10 instances. When users try to exceed this limit, they receive an error message indicating that the DB Instance quota has been exceeded for that specific license model and engine.

For SQL Server on RDS, AWS includes the software license in the pricing (you don't need to purchase SQL Server licenses separately), and there are similar quotas in place. The specific limits can vary based on the SQL Server edition you're using (Enterprise, Standard, Web, or Express).

If you need to increase your quota for SQL Server Standard "license-included" instances, you can request a quota increase through AWS Support. To do this:

1. Go to AWS Support
2. Under "Account and Billing," click "Create case"
3. Select "Looking for service quota increases?"
4. Provide the necessary details about your request for additional SQL Server Standard licenses

AWS will review your request and may approve an increase based on your specific use case and requirements. Alternatively, if you have your own SQL Server licenses, you might consider exploring the "bring-your-own-license" option for some of your workloads, which typically has higher quotas.
Sources
Oracle RDS SE2 licensing quota | AWS re:Post
Licensing Microsoft SQL Server on Amazon RDS - Amazon Relational Database Service
RDS SQL Server database limit | AWS re:Post

I reckon this is a hard limit as per AWS and Microsoft contract. This is stated under Microsoft products with License Mobility through Software Assurance section in https://docs.aws.amazon.com/prescriptive-guidance/latest/migration-microsoft-workloads-aws/licensing-microsoft-workloads.html