Using IPv6 with `vpc_attachments[].vpc_route_table_ids` fails

Jarodiv commented 1 year ago

Description

The module generally supports the use of IPv6. But when adding routes to the tables provided via vpc_attachments[].vpc_route_table_ids, it always tries to assign the vpc_attachments[].tgw_destination_cidr to the IPv4 aws_route.destination_cidr_block argument. Correct would be using aws_route.destination_cidr_block for IPv4 and aws_route.destination_ipv6_cidr_block for IPv6.

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

Versions

Module version [Required]: 2.8.2
Terraform version:
```
Terraform v1.3.7
on darwin_arm64
```

Provider version(s):

provider registry.terraform.io/hashicorp/aws v4.46.0

Reproduction Code [Required]

Everything it needs is to configure IPv6 and provide VPC Route Tables:

module "my_vpc_ipv6" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "~> 3.0"

  name = "my-vpc-ipv6"
  cidr = "10.1.0.0/16"

  azs             = ["${local.region}a", "${local.region}b"]
  private_subnets = ["10.1.1.0/24", "10.1.2.0/24"]
  public_subnets  = ["10.1.101.0/24", "10.1.102.0/24"]

  enable_nat_gateway = false

  enable_ipv6                     = true
  assign_ipv6_address_on_creation = true

  private_subnet_assign_ipv6_address_on_creation = false

  public_subnet_ipv6_prefixes  = [0, 1]
  private_subnet_ipv6_prefixes = [2, 3]
}

module "my_tgw_ipv6" {
  source  = "terraform-aws-modules/transit-gateway/aws"
  version = "~> 2.0"

  name = "my-tgw-ipv6"

  vpc_attachments = {
    vpc = {
      vpc_id     = module.my_vpc_ipv6.vpc_id
      subnet_ids = module.my_vpc_ipv6.private_subnets

      ipv6_support         = true
      tgw_destination_cidr = "::/0"
      vpc_route_table_ids  = module.my_vpc_ipv6.private_route_table_ids
    },
  }
}

Expected behavior

The code runs and IPv6 routes are being created.

Actual behavior

The code would fails because of issue https://github.com/terraform-aws-modules/terraform-aws-transit-gateway/issues/100, but else it would fail, trying to assign an IPv6 CIDR to the IPv4 aws_route.destination_cidr_block instead of using its IPv6 counterpart aws_route.destination_ipv6_cidr_block.