correction

tp-cloud/terraform/environments/dev/outputs.tf

@@ -13,3 +13,7 @@ output "vpc_id" {
 output "service_account_email" {
   value = module.iam.service_account_email
 }
+
+output "subnets_ids" {
+  value = module.network.subnets_ids
+}

tp-cloud/terraform/modules/network/outputs.tf

@@ -1,15 +1,11 @@
-output "frontend_subnet_id" {
-  value = google_compute_subnetwork.frontend.id
-}
-
-output "backend_subnet_id" {
-  value = google_compute_subnetwork.backend.id
-}
-
-output "database_subnet_id" {
-  value = google_compute_subnetwork.database.id
-}
-
 output "vpc_id" {
   value = google_compute_network.vpc.id
 }
+
+output "subnets_ids" {
+  value = [
+    google_compute_subnetwork.frontend.id,
+    google_compute_subnetwork.backend.id,
+    google_compute_subnetwork.database.id
+  ]
+}