'google_compute_instance' adding 'google_compute_disk' forces new resource

[hashibot]

This issue was originally opened by @advanderveer as hashicorp/terraform#6678. It was migrated here as part of the provider split. The original body of the issue is below.

---

Hey, i've encountered unexpected behaviour while updating a google_compute_instance resource by adding a new disk {}.

Terraform Version

Terraform v0.6.16

Affected Resource(s)

• google_compute_instance
• google_compute_disk

Terraform Configuration Files

Consider starting out with the following configuration:

variable "gce_ssh_user" {}
variable "gce_ssh_pub_key_file" {}
variable "gce_service_account" {}
variable "gce_project_id" {}
variable "gce_image" {}
variable "gce_region" {
  default = "europe-west1"
}

variable "gce_network" {}
variable "gce_subnetwork" {}

provider "google" {
  credentials = "${file(var.gce_service_account)}"
  project     = "${var.gce_project_id}"
  region      = "${var.gce_region}"
}

resource "google_compute_disk" "default" {
  name  = "test-disk"
  type  = "pd-ssd"
  zone = "${var.gce_region}-b"
  size = 10
}

resource "google_compute_instance" "remove-me" {
  name       = "disk-test"
  machine_type         = "n1-standard-1"
  can_ip_forward       = false
  zone = "${var.gce_region}-b"

  disk {
    image = "ubuntu-1604-xenial-v20160429"
  }

  network_interface {
    subnetwork = "${var.gce_subnetwork}"
    access_config {
      // Ephemeral IP
    }
  }

  service_account {
    scopes = ["compute-rw"] 
  }

  metadata {
    sshKeys = "${var.gce_ssh_user}:${file(var.gce_ssh_pub_key_file)}"
  }
}

When using the gce interface I would now be able to add the disk 'test-disk' to the instance 'remove-me' without recreating it (or even rebooting). I would expect terraform to behave the same when changing the resource configuration to the following:

variable "gce_ssh_user" {}
variable "gce_ssh_pub_key_file" {}
variable "gce_service_account" {}
variable "gce_project_id" {}
variable "gce_image" {}
variable "gce_region" {
  default = "europe-west1"
}

variable "gce_network" {}
variable "gce_subnetwork" {}

provider "google" {
  credentials = "${file(var.gce_service_account)}"
  project     = "${var.gce_project_id}"
  region      = "${var.gce_region}"
}

resource "google_compute_disk" "default" {
  name  = "test-disk"
  type  = "pd-ssd"
  zone = "${var.gce_region}-b"
  size = 10
}

resource "google_compute_instance" "remove-me" {
  name       = "disk-test"
  machine_type         = "n1-standard-1"
  can_ip_forward       = false
  zone = "${var.gce_region}-b"

  disk {
    image = "ubuntu-1604-xenial-v20160429"
  }

  #DISK ADDED HERE (using .name attribute instead of self_link yields the same result)
  disk {
    disk = "${google_compute_disk.default.self_link}"
  }

  network_interface {
    subnetwork = "${var.gce_subnetwork}"
    access_config {
      // Ephemeral IP
    }
  }

  service_account {
    scopes = ["compute-rw"] //this grands our filesystemd to modify itself
  }

  metadata {
    sshKeys = "${var.gce_ssh_user}:${file(var.gce_ssh_pub_key_file)}"
  }
}

Debug Output

https://gist.github.com/advanderveer/fc9e8ef73f1f0b0b8578fedf9140307e

Panic Output

No panic is produced

Expected Behavior

I would expect the the 'google_compute_instance' not to be recreated

Actual Behavior

It get destroyed, i.e terraform plan shows multiple "forces new resource":

-/+ google_compute_instance.remove-me
    can_ip_forward:                                      "false" => "false"
    disk.#:                                              "1" => "2" **(forces new resource)**
    disk.0.auto_delete:                                  "true" => "true"
    disk.0.image:                                        "ubuntu-1604-xenial-v20160429" => "ubuntu-1604-xenial-v20160429"
    disk.1.auto_delete:                                  "" => "true" **(forces new resource)**
    disk.1.disk:                                         "" => "https://www.googleapis.com/compute/v1/projects/microfactory-test/zones/europe-west1-b/disks/test-disk" (forces new resource)
    machine_type:                                        "n1-standard-1" => "n1-standard-1"
    metadata.#:                                          "1" => "1"
    metadata.sshKeys:                                    "<my public ssh key>"
    metadata_fingerprint:                                "Mq9VPCUvh-E=" => "<computed>"
    name:                                                "disk-test" => "disk-test"
    network_interface.#:                                 "1" => "1"
    network_interface.0.access_config.#:                 "1" => "1"
    network_interface.0.access_config.0.assigned_nat_ip: "146.148.15.98" => "<computed>"
    network_interface.0.address:                         "10.0.0.3" => "<computed>"
    network_interface.0.name:                            "nic0" => "<computed>"
    network_interface.0.subnetwork:                      "microfactory-subnetwork" => "microfactory-subnetwork"
    self_link:                                           "https://www.googleapis.com/compute/v1/projects/microfactory-test/zones/europe-west1-b/instances/disk-test" => "<computed>"
    service_account.#:                                   "1" => "1"
    service_account.0.email:                             "[email protected]" => "<computed>"
    service_account.0.scopes.#:                          "1" => "1"
    service_account.0.scopes.299962681:                  "https://www.googleapis.com/auth/compute" => "https://www.googleapis.com/auth/compute"
    tags_fingerprint:                                    "42WmSpB8rSM=" => "<computed>"
    zone:                                                "europe-west1-b" => "europe-west1-b"

Steps to Reproduce

Please list the steps required to reproduce the issue, for example:

1. terraform plan
2. terraform apply

Important Factoids

Not that i'm aware of

References

I couldn't find any maybe hashicorp/terraform#5241 is related

[danawillow]

Update here- the changes to add boot/scratch disk have been submitted, and disk has been deprecated. The next release will include #329, which adds a state migration so people can upgrade Terraform without changing their configurations. After that, there are a few more steps as detailed in #122.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 [email protected]. Thanks!