feat: add alb_internal_default_target_group_arn variable

Allow users to specify a custom target group ARN for the internal ALB
HTTPS listener default action. If not specified, falls back to the
default target group created by the module.

This enables external deployment tools (e.g., GitHub Actions) to manage
the listener default action without Terraform reverting changes.

Author: thiago4go

_variables.tf

@@ -132,6 +132,12 @@ variable "alb_internal_ssl_policy" {
   description = "The name of the SSL Policy for the listener. Required if protocol is HTTPS or TLS."
 }
 
+variable "alb_internal_default_target_group_arn" {
+  default     = ""
+  type        = string
+  description = "ARN of target group to use as default action for internal ALB HTTPS listener. If empty, uses the default target group created by the module."
+}
+
 variable "alb_drop_invalid_header_fields" {
   default     = true
   type        = bool

alb-internal.tf

@@ -44,7 +44,7 @@ resource "aws_lb_listener" "ecs_https_internal" {
 
   default_action {
     type             = "forward"
-    target_group_arn = aws_lb_target_group.ecs_default_https_internal[0].arn
+    target_group_arn = var.alb_internal_default_target_group_arn != "" ? var.alb_internal_default_target_group_arn : aws_lb_target_group.ecs_default_https_internal[0].arn
   }
 
   tags = merge(