[Bug]: aws_backup_selection selection_tag and resources do not interact as expected

[DerekTBrown]

Terraform Core Version

1.7.5

AWS Provider Version

5.86.0

Affected Resource(s)

• aws_backup_selection

Expected Behavior

Expected Behavior: Backup plan targets S3 buckets with the enable_backup = true tag.¹

Actual Behavior

Actual Behavior: Backup plan targets all S3 buckets AND all AWS resources with theenable_backup = true tag.

Terraform Configuration Files

resource "aws_backup_selection" "backup_selection_usw2" {
  provider = aws.usw2

  name         = "my-backup-plan"
  plan_id      = aws_backup_plan.s3_bucket_backup.id
  iam_role_arn = data.aws_iam_role.backup_default_role.arn

  resources = [
    "arn:aws:s3:::*"
  ]

  selection_tag {
    key   = "enable_backup"
    value = "true"
    type  = "STRINGEQUALS"
  }
}

Steps to Reproduce

1. Apply the given configuration.
2. Observe the AWS resources added to the AWS Vault of choice.

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

None

Footnotes

1. https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/backup_selection#:~:text=selection_tag%20%2D%20(Optional)%20Tag%2Dbased%20conditions%20used%20to%20specify%20a%20set%20of%20resources%20to%20assign%20to%20a%20backup%20plan. ↩

[github-actions]

Community Note

Voting for Prioritization

• Please vote on this issue by adding a 👍 reaction to the original post to help the community and maintainers prioritize this request.
• Please see our prioritization guide for information on how we prioritize.
• Please do not leave "+1" or other comments that do not add relevant new information or questions, they generate extra noise for issue followers and do not help prioritize the request.

Volunteering to Work on This Issue

• If you are interested in working on this issue, please leave a comment.
• If this would be your first contribution, please review the contribution guide.

[DerekTBrown]

The solution is to use the condition field instead of selection_tag:

https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/backup_selection#:~:text=condition%20%2D%20(Optional)%20A%20list%20of%20conditions%20that%20you%20define%20to%20assign%20resources%20to%20your%20backup%20plans%20using%20tags.

However, we should:

• At a minimum, document this better.
• Ideally, change the interface to make it hard to miss this.

This can quickly create significant costs.