Only use local networking for cloudsql.

terraform/modules/cloudsql/cloudsql.tf

@@ -20,6 +20,11 @@ variable "db_version" {
   default     = "POSTGRES_13"
 }
 
+variable "private_network_id" {
+  description = "Private network id."
+  type        = string
+}
+
 resource "google_sql_database_instance" "instance" {
   project = var.project
   region  = var.region
@@ -29,6 +34,11 @@ resource "google_sql_database_instance" "instance" {
 
   settings {
     tier = var.tier
+
+    ip_configuration {
+      ipv4_enabled    = false
+      private_network = var.private_network_id
+    }
   }
 
   deletion_protection = "true"