Add instance metadata to an already running gcp compute instance with terraform

Question

I already have a vm instance running in GCP.Is there a way we can add custom metadata to it using terraform. Terraform has a resource to add custom metadata to a project but not a instance.

I tried to update it by using the google_compute_instance resource by setting the lifecycle.prevent_destroy = true but that does not seem the correct way.

data "google_compute_instance" "instance" {
  name    = var.instance_name
  project = var.project_id
  zone    = var.zone
}


resource "google_compute_instance" "instance" {
  name         = data.google_compute_instance.instance.name
  machine_type = data.google_compute_instance.instance.machine_type
  project = var.project_id
  zone = var.zone
 
# ... rest of the config

  metadata = {
    foo = "bar"
  }
  lifecycle {
    prevent_destroy = true
  }
}

But I get an error saying instance already exists which suggests that it is trying to create a new one but not update.

Answer 1

Instead of the data block you need an import block (https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_instance#import), otherwise Terraform would try to create it.