Added conditional project designation feature for relevant modules.

modules/dns-managed-zone/main.tf

@@ -1,7 +1,9 @@
+data "google_client_config" "default" {}
+
 resource "google_dns_managed_zone" "zone" {
   dns_name = var.dns_name
   name     = var.zone_name != null ? var.zone_name : "${replace(replace(var.dns_name, "/\\.$/", ""), ".", "-")}-zone"
-  project  = var.project_id
+  project  = var.project_id != null ? var.project_id : data.google_client_config.default.project
 
   visibility = var.network_id != null ? "private" : "public"
 
@@ -38,7 +40,7 @@ resource "google_dns_managed_zone" "zone" {
 
 resource "google_dns_record_set" "records" {
   count   = length(var.resource_records)
-  project = var.project_id
+  project = var.project_id != null ? var.project_id : data.google_client_config.default.project
 
   managed_zone = google_dns_managed_zone.zone.name
   name         = var.resource_records[count.index].name

modules/dns-managed-zone/variables.tf

@@ -1,6 +1,8 @@
 variable "project_id" {
-  description = "The project ID where the managed zone will be created."
+  description = "The GCP project ID. If not provided, the default project will be used."
   type        = string
+  nullable    = true
+  default     = null
 }
 
 variable "dns_name" {