[Bug]: Changing to IO2 storage on RDS instance fails

[nhenjes]

Terraform Core Version

1.4.6

AWS Provider Version

5.40.0

Affected Resource(s)

• resource/aws_db_instance

Expected Behavior

We should be able to switch from gp3 with provisioned iops to io2 without changing the allocated storage

Actual Behavior

When changing from gp3 to io2, AWS expects the allocated storage to be passed. Because this value didn't change however, the call to the AWS API excludes the allocated storage value and produces the error

│ Error: updating RDS DB Instance (<database-name>): operation error RDS: ModifyDBInstance, https response error StatusCode: 400, RequestID: <request-id>, api error InvalidParameterCombination: You must specify both the storage size and iops when modifying the storage size or iops on a DB instance that has iops.

Creating a new database with io2 works however because it's a new value that Terraform passes to the API

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

data "aws_rds_orderable_db_instance" "custom-sqlserver" {
  engine                     = "custom-sqlserver-se"
  engine_version             = "15.00.4249.2.v1"
  storage_type               = "gp3"
  preferred_instance_classes = ["db.r5.xlarge", "db.r5.2xlarge", "db.r5.4xlarge"]
}

# The RDS instance resource requires an ARN. Look up the ARN of the KMS key.
data "aws_kms_key" "by_id" {
  key_id = "example-ef278353ceba4a5a97de6784565b9f78" # KMS key
}

resource "aws_db_instance" "example" {
  allocated_storage                     = 500
  auto_minor_version_upgrade  = false
  custom_iam_instance_profile = "AWSRDSCustomSQLServerInstanceProfile"
  backup_retention_period        = 7
  db_subnet_group_name          = local.db_subnet_group_name # Copy the subnet group from the RDS Console
  engine                                        = data.aws_rds_orderable_db_instance.custom-sqlserver.engine
  engine_version                          = data.aws_rds_orderable_db_instance.custom-sqlserver.engine_version
  identifier                                     = "sql-instance-demo"
  instance_class                           = data.aws_rds_orderable_db_instance.custom-sqlserver.instance_class
  kms_key_id                                = data.aws_kms_key.by_id.arn
  multi_az                                      = false # Custom for SQL Server does support multi-az
  password                                    = "avoid-plaintext-passwords"
  storage_encrypted                    = true
  storage_type.                             = "gp3"
  username                                    = "test"

  timeouts {
    create = "3h"
    delete = "3h"
    update = "3h"
  }
}

Steps to Reproduce

Create an RDS instance with gp3, then change only the storage type from gp3 to io2

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

Yes

[github-actions]

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[github-actions]

Warning

This issue has been closed, meaning that any additional comments are hard for our team to see. Please assume that the maintainers will not see them.

Ongoing conversations amongst community members are welcome, however, the issue will be locked after 30 days. Moving conversations to another venue, such as the AWS Provider forum, is recommended. If you have additional concerns, please open a new issue, referencing this one where needed.

[github-actions]

This functionality has been released in v5.78.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.