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terraform-aws-modules / terraform-aws-vpc

Terraform module to create AWS VPC resources 🇺🇦
https://registry.terraform.io/modules/terraform-aws-modules/vpc/aws
Apache License 2.0
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ipv6 vpc not compatible with ipv4 subnet defaults #922

Closed jdix531 closed 1 year ago

jdix531 commented 1 year ago

Description

There has been a recent change in behavior that I think is best identified as a bug. I believe the issue only surfaces during module upgrading so possibly not if upgrading is not always expected to go cleanly. I didn't see any mention in breaking changes for this specific case so perhaps it should just be mentioned on the release page as a breaking condition / corner case.

We had ipv6 enabled on the VPC level but not on the subnet level - we tried upgrading the vpc module (ok, left it with no version defined). I discovered that having ipv6 enabled on the vpc but without subnets having ipv6 initialized (probably a result of created by an older version, current version seems to do this correctly) caused the subnet resources to think ipv6 dns should be enabled which threw an error when applying because they were enabling ipv6 dns without ipv6 cidr blocks.

This likely only happens on "upgrading" instead of net-new as I see variables that seem to handle initializing subnets with ipv6 cidr when ipv6 is enabled for the vpc.

⚠️ Note

Versions

Terraform v1.4.3-dev
on darwin_arm64

Your version of Terraform is out of date! The latest version
is 1.4.4. You can update by downloading from https://www.terraform.io/downloads.html

Reproduction Code [Required]

Steps to reproduce the behavior:

Create older version with ipv6 enabled on the vpc but not strictly defined for the subnets then upgrade the module later.

Expected behavior

I hope updating the module should be possible in the most scenarios possible.

Actual behavior

image

Terminal Output Screenshot(s)

n/a

Additional context

n/a

bryantbiggs commented 1 year ago

thank you for the issue - we'll need a reproduction to help troubleshoot/triage

Tomperez98 commented 1 year ago

This should work

module "my_private_vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "private-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["${local.az}a", "${local.az}b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]

  enable_ipv6 = true

  enable_nat_gateway     = true
  single_nat_gateway     = true
  one_nat_gateway_per_az = false

}
github-actions[bot] commented 1 year ago

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