Add comment concerning the lifecycle changes

modules/consul-cluster/main.tf

@@ -51,6 +51,14 @@ resource "aws_autoscaling_group" "autoscaling_group" {
   )
 
   lifecycle {
+    # As of AWS Provider 3.x, inline load_balancers and target_group_arns
+    # in an aws_autoscaling_group take precedence over attachment resources.
+    # Since the consul-cluster module does not define any Load Balancers,
+    # it's safe to assume that we will always want to favor an attachment
+    # over these inline properties.
+    #
+    # For further discussion and links to relevant documentation, see
+    # https://github.com/hashicorp/terraform-aws-vault/issues/210
     ignore_changes = [load_balancers, target_group_arns]
   }
 }