When you change the instance type of an AWS RDS instance, the availability zone of the instance has to have available capacity of the selected type.
Some older availability zones (us-east-1a) have more old instance types than new types available. If the instance type you selected is not available in the current zone of the instance you get the error message:
We’re sorry, your request to modify DB instance … has failed.
Cannot modify the instance class because there are no instances of the requested class available in the current instance’s availability zone. Please try your request again at a later time.
To upgrade an RDS instance to a new type that is not available in the current availability zone:
- Find an AZ that has the desired instance type
- Try to launch an instance with the new instance type and see which zones have available capacity
- Change the RDS instance to multi-AZ
- Click the Modify button and change the instance to multi-AZ
- If the secondary instance is not created in a zone that has available capacity of your desired instance type, change the instance back to single-AZ and return to step 2, to set it to multi-AZ again.
- Reboot with failover to the secondary instance to make it the primary instance in the new availability zone
- Click the Actions button and select Reboot
- Select Reboot with failover
- Change the instance back to single-AZ
- Upgrade the instance type