Switch to using an explicit net/subnet.

terraform/modules/networking/networking.tf

@@ -3,11 +3,21 @@ variable "project" {
   type        = string
 }
 
+variable "region" {
+  description = "Region."
+  type        = string
+}
+
 output "private_network_id" {
   description = "Private network id."
   value       = google_compute_network.private_network.id
 }
 
+output "private_subnetwork_id" {
+  description = "Private subnetwork id."
+  value       = google_compute_subnetwork.subnet.id
+}
+
 resource "google_project_service" "servicenetworking" {
   project                    = var.project
   service                    = "servicenetworking.googleapis.com"
@@ -23,6 +33,13 @@ resource "google_compute_network" "private_network" {
   ]
 }
 
+resource "google_compute_subnetwork" "subnet" {
+  name          = "private-subnetwork"
+  ip_cidr_range = "10.100.0.0/16"
+  region        = var.region
+  network       = google_compute_network.private_network.id
+}
+
 resource "google_compute_global_address" "private_ip_address" {
   project       = google_compute_network.private_network.project
   name          = "private-ip-address"