Restore local.region

Given var.region can be null, add another try() to check for a provided value
before falling back to current region.

Author: tvon

modules/service/README.md

@@ -222,6 +222,7 @@ module "ecs_service" {
 | [aws_iam_policy_document.tasks](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/iam_policy_document) | data source |
 | [aws_iam_policy_document.tasks_assume](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/iam_policy_document) | data source |
 | [aws_partition.current](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/partition) | data source |
+| [aws_region.current](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/region) | data source |
 | [aws_subnet.this](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/subnet) | data source |
 
 ## Inputs

modules/service/main.tf

@@ -1,3 +1,6 @@
+data "aws_region" "current" {
+  count = var.create ? 1 : 0
+}
 data "aws_partition" "current" {
   count = var.create ? 1 : 0
 }
@@ -8,6 +11,7 @@ data "aws_caller_identity" "current" {
 locals {
   account_id = try(data.aws_caller_identity.current[0].account_id, "")
   partition  = try(data.aws_partition.current[0].partition, "")
+  region     = try(var.region, try(data.aws_region.current[0].region, ""))
 }
 
 ################################################################################
@@ -1180,7 +1184,7 @@ data "aws_iam_policy_document" "tasks_assume" {
     condition {
       test     = "ArnLike"
       variable = "aws:SourceArn"
-      values   = ["arn:${local.partition}:ecs:${var.region}:${local.account_id}:*"]
+      values   = ["arn:${local.partition}:ecs:${local.region}:${local.account_id}:*"]
     }
 
     condition {