r/aws_network_acl_rule: Prevent creation of duplicate Terraform resources

[ewbankkit]

Define multiple ACL rules with identical attributes but different Terraform resource names.
Example:

resource "aws_network_acl_rule" "original-rule" {
  network_acl_id = aws_network_acl.vpc-test.id
  rule_number = 200
  egress = false
  protocol = "tcp"
  rule_action = "allow"
  cidr_block = "10.0.0.0/24"
  from_port = 22
  to_port = 22
}

resource "aws_network_acl_rule" "new-rule" {
  network_acl_id = aws_network_acl.vpc-test.id
  rule_number = 200
  egress = false
  protocol = "tcp"
  rule_action = "allow"
  cidr_block = "10.0.0.0/24"
  from_port = 22
  to_port = 22
}

• Apply the Terraform configuration.
• Delete one of the ACL rules.
• Observe the unexpected removal of the corresponding Network ACL entry from AWS.

The EC2 CreateNetworkAclEntry API succeeds on the second resource Create if all attributes are identical. Prevent this.

[github-actions]

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[ewbankkit]

Check also aws_route and security group rules.
Routes require the same treatment, security group rules do not: InvalidPermission.Duplicate: the specified rule "peer: 10.0.0.0/8, TCP, from port: 80, to port: 8080, ALLOW" already exists.

[github-actions]

This functionality has been released in v5.41.0 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!

[jhenry82]

So I understand the rationale for fixing the issue of creating duplicate resources. It has left us in a bit of a bind, however. We are using an in-house module that inadvertently created some duplicate aws_route resources. Today we upgraded to the latest provider release, and the module began failing on those duplicate routes. I can easily remove one set of routes from the code. But if I do that, Terraform of course wants to delete the route. Then we have to do another plan and apply so it notices the route is gone, and recreates it using the remaining copy of the aws_route resource. Doing this in production will cause an outage. Which I would really like to avoid. Finding a breaking change in a minor version release is also frustrating, even if it is technically correct.

Do you have any suggested workarounds? I tried using various moved{} blocks in the hopes that would prevent Terraform from deleting the route, but it had no effect. The best I can come up with is making sure we do a "terraform state rm" on the affected routes before applying.

[ewbankkit]

@jhenry82 You should be able to use a removed block.

[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.
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