[Bug]: RDS Cluster Members incorrectly surfaced as an argument

[drakeryswrath]

Terraform Core Version

1.6.6

AWS Provider Version

5.76.0

Affected Resource(s)

aws_rds_cluster
aws_rds_cluster_instance

Expected Behavior

RDS Cluster resource should output the cluster members. It should be invalid to provide cluster members to the resource. The cluster members are already defined as part of the rds cluster instances referencing the cluster. I came across the issue updating a colleagues existing code.

Actual Behavior

The cluster members applies first with the cluster resource and then is updated by the cluster instance resource. It then shows a change everytime a plan or apply runs.

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

I can't share as they were discovered at work. I believe this is the issue. the cluster_members according to docs should only be an attribute but the way it has been defined is as an optional input as well. The relationship input is already covered by the cluster instance as defined by cluster identifier argument.

If the option remains there should need to check its not defined in both and would need to be added to documentation.
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/rds_cluster#attribute-reference

https://github.com/hashicorp/terraform-provider-aws/blob/main/internal/service/rds/cluster.go#L135-L140
"cluster_members": {
Type: schema.TypeSet,
Optional: true,
Computed: true,
Elem: &schema.Schema{Type: schema.TypeString},
},

Steps to Reproduce

1. In Terraform

• create an aws_rds_cluster with an empty list for cluster_members = []
• Create an aws_rds_cluster_instance referencing the cluster as cluster_identifier

2. Apply the first time

3. Then run a plan and it will show as dropping the instance from the cluster.

Fix/workaround:
Remove the cluster_members argument from rds cluster resource

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

Cluster source code issue suspected
https://github.com/hashicorp/terraform-provider-aws/blob/main/internal/service/rds/cluster.go#L135-L140

Documentation from hashicorp
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/rds_cluster

Would you like to implement a fix?

None

[github-actions]

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