Confusing DNS64 behaviour with public subnets

[rvem]

Description

public_subnet_enable_dns64 is true by default and with enable_ipv6 = true; this enables DNS64 for created public subnets.

However, if a given domain doesn't have an IPv6 record, it's resolved to 64:ff9b::/96 which in turn needs an additional route setup
to work correctly.

• ✋ I have searched the open/closed issues and my issue is not listed.

Somewhat similar to #923, but for public subnets.

Versions

• Module version [Required]: 5.1.1

• Terraform version: 1.5.4

• Provider version(s): AWS - 5.10.0

Reproduction Code [Required]

module "aws_vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.1"

  name = local.vpc_name
  cidr = var.vpc_cidr
  azs  = local.azs

  public_subnets  = ["10.0.11.0/24", "10.0.12.0/24", "10.0.13.0/24"]

  enable_ipv6 = true
  assign_ipv6_address_on_creation = true
  enable_dns_hostnames = true
  enable_dns_support = true
  map_public_ip_on_launch = true
  public_subnet_assign_ipv6_address_on_creation = true

  enable_dhcp_options = true
  dhcp_options_domain_name = var.domain_name
  dhcp_options_domain_name_servers = ["AmazonProvidedDNS"]

  public_subnet_ipv6_prefixes  = [0, 1, 2]
}

Steps to reproduce the behavior:

curl -6 api.github.com from the EC2 instance within one of the public subnets above hangs.

Expected behavior

DNS64 enabled along with the corresponding route for resolving 64:ff9b::/96

Actual behavior

An IP from 64:ff9b::/96 is not routed correctly:(

[github-actions]

This issue has been automatically marked as stale because it has been open 30 days
with no activity. Remove stale label or comment or this issue will be closed in 10 days

[rvem]

Still relevant

[JeffreyVdb]

I'm having this issue as well.
Use case is creating a publicly reachable machine with only an IPv6 IP.

There are 2 solutions:

• adding an IPv4 public IP
• adding the route to 64:ff9b::/96

In my case however, I don't need a public IPv4 IP, I do need NAT64.

[github-actions]

This issue has been automatically marked as stale because it has been open 30 days
with no activity. Remove stale label or comment or this issue will be closed in 10 days

[rvem]

Still relevant

[github-actions]

This issue has been automatically marked as stale because it has been open 30 days
with no activity. Remove stale label or comment or this issue will be closed in 10 days

[rvem]

Still relevant