Support google_compute_subnetwork update to IPV6

[ErikEngerd]

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Description

It should be possible to update a subnetwork from IPV4 to dual stack IPV4_IPV6 without recreating the subnetwork.

In concrete, first create an IPV4 subnet:

resource "google_compute_subnetwork" "subnet-lan" {
  provider          = google
  name              = "testsubnet"
  region            = "europe-west4"
  ip_cidr_range     = "10.50.0.0/16"
  network           = "network"
}

Then update it to dual stack:

resource "google_compute_subnetwork" "subnet-lan" {
  provider          = google
  name              = "testsubnet"
  region            = "europe-west4"
  ip_cidr_range     = "10.50.0.0/16"
  network           = "network"
  stack_type        = "IPV4_IPV6"
  ipv6_access_type  = "EXTERNAL"
}

New or Affected Resource(s)

• google_compute_subnetwork

Potential Terraform Configuration

The existing terraform configuration does not need to be changed.

References

Google documentation is confusing and seems to contradict itself by saying:

The access type of IPv6 address this subnet holds. It's immutable and can only be specified during creation or the first time the subnet is updated into IPV4_IPV6 dual stack.

But it says that the update is possible. Updates are also possible through google cloud console.

Also, updates using gcloud commandline work

gcloud compute networks subnets update testsubnet --stack-type=IPV4_IPV6 --ipv6-access-type=EXTERNAL

Debug output from terraform 1.3.2 shows the output of the current version of terraform.

• google_compute_subnetwork migration to ipv6 forces replacement #12833

[ErikEngerd]

When defining a VM that has a network interface in the subnet and updating the VM to go from IPV4 to dual stack then nothing happens and the network interface is still in IPV4. Updating the network interface in the google cloud console works though.

Network interface definition in terraform for a VM:

network_interface { 
  ...
  stack_type = "IPV4_IPV6" 
}

[hao-nan-li]

b/261047629
b/261047894
b/261048516

[melinath]

b/261863885

[melinath]

@trodge I think you might have to assign yourself on the GH issue - I can't seem to do it.

[github-actions]

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