RDS Blue/Green deployment does NOT allow shrinking

While AWS announced that RDS Blue/Green deployments support storage volume shrinking, there appears to be a limitation or potential bug affecting this functionality. Multiple users have reported issues when attempting to reduce storage size using Blue/Green deployments, particularly with PostgreSQL instances.

The current behavior seems inconsistent with the announced feature. When users attempt to create a Green environment with reduced storage, the deployment process appears to acknowledge the requested smaller size during confirmation, but the resulting Green instance maintains the original (or sometimes even larger) storage allocation.

One potential workaround that has been reported to help in some cases is disabling storage autoscaling before initiating the Blue/Green deployment, and then re-enabling it after the switchover is complete.

It's also important to note that there are specific requirements for storage reduction:

• The target allocated storage must be at least 20% more than your current storage usage
• You should calculate your required storage by checking your current usage via CloudWatch FreeStorageSpace metric and adding 20% to determine the minimum target size

If you continue to experience issues with storage shrinking during Blue/Green deployments, it would be advisable to:

1. Document your steps and observations in detail
2. Open a support case with AWS to report the issue
3. Consider alternative approaches such as manually creating a new instance with smaller storage and migrating your data

There is no publicly available information about an estimated time for a fix, but reporting the issue to AWS Support would help bring attention to the problem.
Sources
RDS Blue/Green deployment does NOT allow shrinking | AWS re:Post
RDS blue/green deployment is not decreasing the storage | AWS re:Post
Reduce the RDS MS SQL Storage post data archival | AWS re:Post