feat!: allow to override umig availability zones

Sometimes it's profitable to specify exact list of AZs to use instead of
spreading instances across the available AZs.
Another reason is if you want to iterate over AZs subset in the specific
order (e.g. create 1st VM in a zone different from 1st available).

modules/umig/README.md

@@ -29,6 +29,7 @@ See the [simple](https://github.com/terraform-google-modules/terraform-google-vm
 | static\_ips | List of static IPs for VM instances | `list(string)` | `[]` | no |
 | subnetwork | Subnet to deploy to. Only one of network or subnetwork should be specified. | `string` | `""` | no |
 | subnetwork\_project | The project that subnetwork belongs to | `string` | `""` | no |
+| zones | Override the availability zones list to create the resources in. | `list(string)` | `[]` | no |
 
 ## Outputs
 

modules/umig/main.tf

@@ -23,9 +23,11 @@ locals {
   # determine type" error when var.static_ips is empty
   static_ips = concat(var.static_ips, ["NOT_AN_IP"])
 
+  zones = length(var.zones) == 0 ? data.google_compute_zones.available.names : var.zones
+
   instance_group_count = min(
     local.num_instances,
-    length(data.google_compute_zones.available.names),
+    length(local.zones),
   )
 }
 
@@ -48,7 +50,7 @@ resource "google_compute_instance_from_template" "compute_instance" {
   count    = local.num_instances
   name     = format("%s%s%s", local.hostname, var.hostname_suffix_separator, format("%03d", count.index + 1))
   project  = var.project_id
-  zone     = data.google_compute_zones.available.names[count.index % length(data.google_compute_zones.available.names)]
+  zone     = local.zones[count.index % length(local.zones)]
 
   network_interface {
     network            = var.network
@@ -105,11 +107,11 @@ resource "google_compute_instance_group" "instance_group" {
   count    = local.instance_group_count
   name     = "${local.hostname}-instance-group-${format("%03d", count.index + 1)}"
   project  = var.project_id
-  zone     = element(data.google_compute_zones.available.names, count.index)
+  zone     = element(local.zones, count.index)
   instances = matchkeys(
     google_compute_instance_from_template.compute_instance.*.self_link,
     google_compute_instance_from_template.compute_instance.*.zone,
-    [data.google_compute_zones.available.names[count.index]],
+    [local.zones[count.index]],
   )
 
   dynamic "named_port" {

modules/umig/variables.tf

@@ -115,3 +115,9 @@ variable "hostname_suffix_separator" {
   description = "Separator character to compose hostname when add_hostname_suffix is set to true."
   default     = "-"
 }
+
+variable "zones" {
+  type        = list(string)
+  description = "(Optional) List of availability zones to create VM instances in"
+  default     = []
+}