google_compute_instance infinite diff if min_cpu_platform is set to AUTOMATIC

[jcanseco]

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Terraform Version

Terraform v1.0.2
on linux_amd64
+ provider registry.terraform.io/hashicorp/google v4.1.0

Affected Resource(s)

• google_compute_instance

Terraform Configuration Files

resource "google_compute_instance" "instance" {
  name          = "my-instance"
  machine_type  = "n1-standard-1"
  zone          = "us-west1-a"
  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }
  network_interface {
    network = "default"
  }
  min_cpu_platform = "AUTOMATIC"
}

Expected Behavior

terraform apply-ing this resource and then terraform plan-ing right after should produce no diffs.

Actual Behavior

A diff was produced:

Terraform will perform the following actions:

  # google_compute_instance.instance will be updated in-place
  ~ resource "google_compute_instance" "instance" {
        id                   = "projects/cnrm-jcanseco-2/zones/us-west1-a/instances/my-instance"
      + min_cpu_platform     = "AUTOMATIC"
        name                 = "my-instance"
        tags                 = []
        # (17 unchanged attributes hidden)



        # (3 unchanged blocks hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

Steps to Reproduce

1. terraform apply
2. terraform plan

Notice how there is a diff for min_cpu_platform. Same issue happens if min_cpu_platform is set to Automatic.

I believe the reason behind this behavior is that according to the documentation for minCpuPlatform, you set the field to AUTOMATIC when you want to clear it in the underlying API.

Therefore, when the user applies a google_compute_instance with min_cpu_platform = "AUTOMATIC", the API clears the field as expected, but now Terraform believes there is a diff since the underlying value is empty whereas the user has a specified value.

I believe the fix here is to supress diffs for min_cpu_platform if the user sets it to AUTOMATIC (or Automatic) and the underlying value is empty string since these should actually be treated as equivalent.

References

• b/208316260

[roaks3]

Appears to be fixed by GoogleCloudPlatform/magic-modules#8249

[github-actions]

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