RDS RI Upgradable?

Question

I have an RDS Oracle reserved instance (1 yr, all upfront) with db.r5.8xlarge class. I want to downgrade it to db.r5.4xlarge due to less usage during the next renewal. Can I upgrade it back to db.r5.8xlarge if there are any performance issues after the renewal? I think I have to run modify-db-instance API but is it possible in this scenario?

anish_g · Accepted Answer

Hi,

Adding additional context with respect to Size flexibility and Normalization factor for RDS reserved instances within same instance class including RDS for Oracle.
* Reserved DB instances can be applied flexibly across different DB instance class sizes within the same instance class type (e.g. db.r5.large to db.r5.xlarge).
* The billing benefit of reserved DB instances is based on "normalized units per hour" which vary by DB instance size.
* Size-flexible reserved instances automatically apply across all DB instance class sizes within the same instance class type
* For example, a reserved instance for db.r5.large can apply to db.r5.xlarge, but not to db.r6g.large.
* Please refer to the table under [Size-flexible reserved DB instances](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithReservedDBInstances.html#:~:text=User%20Guide.-,Size%2Dflexible%20reserved%20DB%20instances,-When%20you%20purchase) which provides normalization units that applies to all supported database engines, including Oracle.

High level if you have RDS reserved instance for example - db.r5.4xlarge and upgrade your RDS instance to db.r5.8xlarge, then 50% of the usage will be covered by Reserved instance and other 50% by on-demand charges.

Note : Size flexibility does not apply to RDS for SQL Server and Oracle License Included (BYOL is supported).

re:Post Agent · Answer

When it comes to modifying RDS Oracle reserved instances (RIs), it's important to understand that RIs themselves cannot be directly upgraded or downgraded. Reserved instances are a billing construct and don't directly correspond to a specific DB instance.

However, you can modify your actual RDS Oracle DB instance to change its instance class. In your case, you can downgrade from db.r5.8xlarge to db.r5.4xlarge using the modify-db-instance API or through the AWS Management Console. If you experience performance issues after this change, you can indeed upgrade it back to db.r5.8xlarge using the same method.

It's crucial to note that changing the instance class of your DB instance does not affect your existing RI. Your RI will continue to provide a billing discount for the instance size you originally purchased (db.r5.8xlarge in this case) until its term expires.

When you renew your RI, you can choose a different instance class that better fits your current needs. After renewal, if you need to change the instance class again due to performance issues or changing requirements, you can do so at any time using the modify-db-instance API or the AWS Management Console.

Remember to test your database and application thoroughly after any instance class changes to ensure they can handle the new configuration. Also, be aware that modifying the instance class may result in some downtime during the change.  
**Sources**  
[Upgrading the version of an RDS for Oracle DB instance - Amazon Relational Database Service](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_UpgradeDBInstance.Oracle.Upgrading.html)  
[RDS for Oracle DB instance classes - Amazon Relational Database Service](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Oracle.Concepts.InstanceClasses.html)

RDS RI Upgradable?

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