Taking over existing instances with Terraform

A few days ago, while playing with Terraform I realized that I want Terraform to manage some instances that I had already created in Google Cloud. Because these instances existed before I was using Terraform, it doesn’t konw anything about them.

The first thing I had to do to take over them, was to add them to the configuration:

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resource "google_compute_instance" "us-central1-c--f1-micro--001" {
  name         = "us-central1-c--f1-micro--001"
  machine_type = "f1-micro"
  zone         = "us-central1-c"

  boot_disk {
    initialize_params {
      image = "ubuntu-1604-xenial-v20170815a"
    }
  }

  network_interface {
    network = "default"
  }
}

Once I had the machine in my configuration, I just had to tell Terraform, which machine is that:

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terraform import google_compute_instance.us-central1-c--f1-micro--001 ncona-179804/us-central1-c/us-central1-c--f1-micro--001

From here terraform can manage it as if it had created it.