Setting ip_address to IPv6 for google_compute_forwarding_rule causes recreation

[nkinkade]

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Terraform Version

$ terraform -v
Terraform v1.5.7
on linux_amd64
+ provider registry.terraform.io/hashicorp/google v4.82.0

Affected Resource(s)

• google_compute_forwarding_rule

Terraform Configuration Files

resource "google_compute_address" "my_v6_addr" {
  address_type       = "EXTERNAL"
  ipv6_endpoint_type = "NETLB"
  ip_version         = "IPV6"
  name               = "my-v6-addr"
  region             = "us-east1"
  subnetwork         = "my-subnet"
}

resource "google_compute_forwarding_rule" "my_forwarding_rule" {
  all_ports             = true
  backend_service       = google_compute_region_backend_service.my_backend_service.id
  ip_address            = "${google_compute_address.my_ipv6_addr.address}/96"
  ip_protocol           = "L3_DEFAULT"
  ip_version            = "IPV6"
  load_balancing_scheme = "EXTERNAL"
  name                  = "my-forwarding-rule"
  region                = us-east1
  subnetwork            = my-subnet
}

Debug Output

https://gist.github.com/nkinkade/aaccc5ae60d2d3e1b134c9ed24af608c

Panic Output

Expected Behavior

It should be possible to assign the address attribute of a static IPv6 google_compute_address resource as the ip_address argument of google_compute_forwarding_rule without the forwarding rule being recreated on every run of terraform apply, even it nothing has changed.

Actual Behavior

On every run of terraform apply the google_compute_forwarding_rule is recreated, even when nothing has changed about the Terraform configuration.

The underlying issue seems to be that the address field/attribute of an IPv6 google_compute_address resource will use abbreviated IPv6 notation, collapsing all-zero "hextets" and without a prefix value e.g., 2600:1900:4020:31cd:8000::. However, the API appears to expand the ip_address argument (IPAddress field) of a google_compute_forwarding_rule such that the above example IPv6 google_compute_address is stored as 2600:1900:4020:31cd:8000:0:0:0/96. Terraform (or perhaps the API?) sees these as two different addresses/values and wants to recreate the forwarding rule using the abbreviated address value, as stored in the google_compute_address resource. This will happen as many times as you run terraform apply.

Using google_compute_address.my_ipv6_addr.id or google_compute_address.my_ipv6_addr.self_link as the value of ip_address in the forwarding rule creates a similar problem, but more like the one described in #7841.

Details of the created resources as reported by gcloud (abbreviated to relevant fields):

$ gcloud compute addresses describe my-ipv6-address --region us-east1 --project my-project
address: '2600:1900:4020:31cd:8000::'
addressType: EXTERNAL
ipVersion: IPV6
ipv6EndpointType: NETLB
kind: compute#address
prefixLength: 96

$ gcloud compute forwarding-rules describe my-ipv6-fwd-rule --region us-east1 --project my-project
IPAddress: 2600:1900:4020:31cd:8000:0:0:0/96
ipVersion: IPV6
kind: compute#forwardingRule
loadBalancingScheme: EXTERNAL

Steps to Reproduce

1. Define a regional, static IPv6 google_compute_address resource (e.g., google_compute_address.my_ipv6_addr)
2. Use ${google_compute_address.my_ipv6_addr.address}/96 as the value of the ip_address argument of a google_compute_forwarding_rule resource.
3. Run terraform apply... the forwarding rule resources will be recreated.
4. Run terraform apply ... the forwarding rule resource will be recreated.
5. [...]

Important Factoids

Nothing special.

References

• google_compute_instance network_ip selflink reference causes re-creation. #7841

[edwardmedia]

Yes, this is a bug

-/+ resource "google_compute_forwarding_rule" "platform_cluster_mig_forwarding_rules_v6" {

      ~ ip_address              = "2600:1900:4020:31cd:8000:0:0:0/96" -> "2600:1900:4020:31cd:8000::/96" # forces replacement
   
        # (5 unchanged attributes hidden)
    }

The diff suppress function needs update

[edwardmedia]

Below format is possible and legit

"2600:1900:4000:1077:8000:0:0:0/96" -> "https://www.googleapis.com/compute/v1/projects/myproject/regions/us-central1/addresses/myaddress" # forces replacement

[nkinkade]

In my experiments, all of these are accepted by both Terraform and the Google API, but they also all result in the forwarding rule being recreated on every run of terraform {plan,apply}:

• "${google_compute_address.my_ipv6_addr.address}/96"
• google_compute_address.my_ipv6_addr.id
• google_compute_address.my_ipv6_addr.self_link

If I use the .address attribute I have to append "/96", otherwise the Google API rejects the value as invalid.

[github-actions]

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