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Terraform Version & Provider Version(s)

Terraform v1.10.5
on darwin_arm64

• provider registry.terraform.io/hashicorp/google v6.21.0

Affected Resource(s)

• google_compute_instance
• google_compute_subnetwork
• google_compute_network

Terraform Configuration

resource "google_compute_network" "vpc_network" {
  project                 = "my-project"
  name                    = "terraform-network"
  auto_create_subnetworks = "false"
  enable_ula_internal_ipv6 = true
}

resource "google_compute_subnetwork" "subnetwork" {
  project = "my-project"
  name    = "ipv6-test-subnetwork"

  ip_cidr_range = "10.0.0.0/22"
  region        = "us-central1"

  stack_type       = "IPV4_IPV6"
  ipv6_access_type = "INTERNAL"

  network = google_compute_network.vpc_network.id
}

resource "google_compute_instance" "vm_instance" {
  project                   = "my-project"
  name                      = "terraform-instance"
  machine_type              = "e2-micro"
  zone                      = "us-central1-c"
  boot_disk {
    auto_delete = false
    initialize_params {
      image = "debian-cloud/debian-11"
    }
  }
  network_interface {
    network    = google_compute_network.vpc_network.self_link
    subnetwork = google_compute_subnetwork.subnetwork.self_link
    stack_type = "IPV4_IPV6"
    access_config {
      network_tier = "STANDARD"
    }
    internal_ipv6_prefix_length = 96 # GCP NOT SYNCING ATTRIBUTE WITH TERRAFORM
  }
}

Debug Output

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # google_compute_instance.vm_instance will be updated in-place
  ~ resource "google_compute_instance" "vm_instance" {
        id                         = "projects/my-project/zones/us-central1-c/instances/terraform-instance"
        name                       = "terraform-instance"
        tags                       = []
        # (23 unchanged attributes hidden)

      ~ network_interface {
          ~ internal_ipv6_prefix_length = 0 -> 96
            name                        = "nic0"
            # (9 unchanged attributes hidden)

            # (1 unchanged block hidden)
        }

        # (3 unchanged blocks hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.
google_compute_instance.vm_instance: Modifying... [id=projects/iac-lifting-test/zones/us-central1-c/instances/terraform-instance]

Expected Behavior

After terraform apply once using the configuration above and terraform apply again without any modification on the configuration, nothing should be changed.

Actual Behavior

Terraform thinks the google_compute_instance.network_interface.internal_ipv6_prefix_length is 0 instead of 96 as specified in the configuration, so it plans again and again with the debug output above. What's worse, this trigger the plugin crash as described in #21505

Steps to reproduce

1. terraform apply to create all the resource
2. terraform apply again, then we'll see the debug output above as well as the crash message in Google provider plugin crashed when adding network_interface.internal_ipv6_prefix_length in compute_instance #21505

Important Factoids

No response

References

No response