[Bug]: enable IPv6, apply error occurred

[watarukura]

Terraform Core Version

1.5.4

AWS Provider Version

5.11.0

Affected Resource(s)

• aws_subnet

Expected Behavior

The expected behavior was to associate an ipv6_cidr_block with an aws_subnet where ipv6_cidr_block was originally null. At the same time, I intended to set enable_dns64 and enable_resource_name_dns_aaaa_record_on_launch to true.

  # module.network.module.subnet["subnet-1a_1"].aws_subnet.this will be updated in-place
  ~ resource "aws_subnet" "this" {
      ~ assign_ipv6_address_on_creation                = false -> (known after apply)
      ~ enable_dns64                                   = false -> (known after apply)
      ~ enable_resource_name_dns_aaaa_record_on_launch = false -> (known after apply)
        id                                             = "subnet-0cf3edac22636b4fa"
      + ipv6_cidr_block                                = (known after apply)
        tags                                           = {
            "Name" = "subnet-1a_1"
        }
        # (13 unchanged attributes hidden)
    }

Actual Behavior

the actual behavior encountered an error, preventing the ability to set enable_dns64 to true due to the requirement of having an associated ipv6_cidr_block.

Relevant Error/Panic Output Snippet

Error: modifying EC2 Subnet (subnet-0cf3edac22636b4fa) EnableDns64: InvalidParameterValue: Invalid value 'true' for enable-dns64. Cannot set enable-dns64 to true unless the subnet (subnet-0cf3edac22636b4fa) has an IPv6 CIDR block associated with it.
	status code: 400, request id: 06223ea1-c744-421f-bed1-7801a1532c10

  with module.network.module.subnet["subnet-1a_1"].aws_subnet.this,
  on .terraform/modules/network.subnet/aws/subnet/subnet.tf line 6, in resource "aws_subnet" "this":
   6: resource "aws_subnet" "this" {

Terraform Configuration Files

terraform {
  required_version = ">= 1.1.0"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = ">= 5.0.0"
    }
  }
}

Steps to Reproduce

1. Create IPv4 only vpc and subnet

locals {
  cidr_block = "172.31.0.0/16"
  az         = "ap-northeast-1a"
  subnet_cidr_block = cidrsubnet(local.cidr_block, 8, 1)
}

resource "aws_vpc" "vpc" {
  cidr_block                       = local.cidr_block
  assign_generated_ipv6_cidr_block = false
}

resource "aws_internet_gateway" "gateway" {
  vpc_id = aws_vpc.vpc.id
}

resource "aws_subnet" "this" {
  cidr_block        = local.subnet_cidr_block
  vpc_id            = aws_vpc.vpc.id
  availability_zone = local.az

  ipv6_cidr_block                                = null
  enable_dns64                                   = false
  assign_ipv6_address_on_creation                = false
  enable_resource_name_dns_aaaa_record_on_launch = false
}

2. Enable IPv6

locals {
  cidr_block = "172.31.0.0/16"
  az         = "ap-northeast-1a"
  subnet_cidr_block = cidrsubnet(local.cidr_block, 8, 1)
}

resource "aws_vpc" "vpc" {
  cidr_block                       = local.cidr_block
  assign_generated_ipv6_cidr_block = false
}

resource "aws_internet_gateway" "gateway" {
  vpc_id = aws_vpc.vpc.id
}

resource "aws_subnet" "this" {
  cidr_block        = local.subnet_cidr_block
  vpc_id            = aws_vpc.vpc.id
  availability_zone = local.az

  ipv6_cidr_block                                = cidrsubnet(aws_vpc.vpc.ipv6_cidr_block, 8, 1)
  enable_dns64                                   = true
  assign_ipv6_address_on_creation                = true
  enable_resource_name_dns_aaaa_record_on_launch = true
}

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]

This functionality has been released in v5.13.0 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]

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