Fixes for GKE

* Fix non-empty plan when spot instances are used
* Add cluster_id and recommend its use, as this prevents inconsitencies
  when only cluster is recreated (with no changes on node pool)

blueprints/networking/shared-vpc-gke/main.tf

@@ -221,12 +221,12 @@ module "cluster-1" {
 }
 
 module "cluster-1-nodepool-1" {
-  source       = "../../../modules/gke-nodepool"
-  count        = var.cluster_create ? 1 : 0
-  name         = "nodepool-1"
-  project_id   = module.project-svc-gke.project_id
-  location     = module.cluster-1.0.location
-  cluster_name = module.cluster-1.0.name
+  source     = "../../../modules/gke-nodepool"
+  count      = var.cluster_create ? 1 : 0
+  name       = "nodepool-1"
+  project_id = module.project-svc-gke.project_id
+  location   = module.cluster-1.0.location
+  cluster_id = module.cluster-1.0.id
   service_account = {
     create = true
   }

modules/gke-cluster/main.tf

@@ -17,7 +17,8 @@
 resource "google_container_cluster" "cluster" {
   lifecycle {
     ignore_changes = [
-      node_config[0].boot_disk_kms_key
+      node_config[0].boot_disk_kms_key,
+      node_config[0].spot
     ]
   }
   provider    = google-beta

modules/gke-nodepool/main.tf

@@ -70,7 +70,7 @@ resource "google_service_account" "service_account" {
 resource "google_container_node_pool" "nodepool" {
   provider           = google-beta
   project            = var.project_id
-  cluster            = var.cluster_name
+  cluster            = coalesce(var.cluster_id, var.cluster_name)
   location           = var.location
   name               = var.name
   version            = var.gke_version

modules/gke-nodepool/variables.tf

@@ -14,9 +14,16 @@
  * limitations under the License.
  */
 
+variable "cluster_id" {
+  description = "Cluster id. Either cluster_id or cluster_name must be provided. Providing cluster_id is recommended."
+  type        = string
+  default     = null
+}
+
 variable "cluster_name" {
-  description = "Cluster name."
+  description = "Cluster name. Either cluster_id or cluster_name must be provided. Providing cluster_id is recommended."
   type        = string
+  default     = null
 }
 
 variable "gke_version" {