can't remove ipv6_cidr_block from aws_subnet

[dmrzzz]

Removing a previously-applied ipv6_cidr_block parameter from aws_subnet does not produce the expected behavior of removing the IPv6 CIDR.

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Terraform Version

Terraform v0.12.13
+ provider.aws v2.35.0

Affected Resource(s)

• aws_subnet

Terraform Configuration Files

provider "aws" {
  region = "us-west-2"
}

resource "aws_vpc" "vpc" {
  cidr_block = "192.168.0.0/24"
  assign_generated_ipv6_cidr_block = true
}

resource "aws_subnet" "subnet" {
  vpc_id          = aws_vpc.vpc.id
  cidr_block      = "192.168.0.0/26"
  #ipv6_cidr_block = cidrsubnet(aws_vpc.vpc.ipv6_cidr_block, 8, 0)
}

output "subnet" {
  value = aws_subnet.subnet
}

Steps to Reproduce

1. terraform apply

   creates the VPC (with IPv6) and subnet (IPv4-only), as expected

2. Uncomment the ipv6_cidr_block line

3. terraform apply

   updates the subnet in-place to add ipv6_cidr_block, as expected

4. Re-comment the ipv6_cidr_block line

5. terraform apply

   Expected: should update the subnet to remove ipv6_cidr_block
   Actual: apply completes immediately with no changes, and my subnet still has IPv6

[bflad]

The fix for this has been merged and will release with version 3.3.0 of the Terraform AWS Provider, shortly. Thanks to @DrFaust92 for the implementation. 👍

[ghost]

This has been released in version 3.3.0 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 for triage. Thanks!

[ghost]

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 feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!