Add optional network_interface_id variable

main.tf

@@ -94,11 +94,12 @@ resource "aws_launch_template" "default" {
 
   # https://github.com/terraform-providers/terraform-provider-aws/issues/4570
   network_interfaces {
-    description                 = module.this.id
+    description                 = var.network_interface_id == null ? module.this.id : null
     device_index                = 0
-    associate_public_ip_address = var.associate_public_ip_address
-    delete_on_termination       = true
-    security_groups             = var.security_group_ids
+    associate_public_ip_address = var.network_interface_id == null ? var.associate_public_ip_address : null
+    delete_on_termination       = var.network_interface_id == null ? true : false
+    security_groups             = var.network_interface_id == null ? var.security_group_ids : null
+    network_interface_id        = var.network_interface_id
   }
 
   metadata_options {
@@ -149,7 +150,8 @@ resource "aws_autoscaling_group" "default" {
   count = module.this.enabled ? 1 : 0
 
   name_prefix               = format("%s%s", module.this.id, module.this.delimiter)
-  vpc_zone_identifier       = var.subnet_ids
+  vpc_zone_identifier       = var.availability_zones == null ? var.subnet_ids : null
+  availability_zones        = var.subnet_ids == null ? var.availability_zones : null
   max_size                  = var.max_size
   min_size                  = var.min_size
   load_balancers            = var.load_balancers

variables.tf

@@ -40,11 +40,18 @@ variable "launch_template_version" {
 }
 
 variable "associate_public_ip_address" {
-  type        = bool
-  description = "Associate a public IP address with an instance in a VPC"
+  type = bool
+  # https://stackoverflow.com/a/76808361
+  description = "Associate a public IP address with an instance in a VPC. If a network_interface id is specified, this can only be false."
   default     = false
 }
 
+variable "network_interface_id" {
+  type        = string
+  description = "The ID of the network interface to attach. If specified, all the other network_interface block arguments are ignored."
+  default     = null
+}
+
 variable "user_data_base64" {
   type        = string
   description = "The Base64-encoded user data to provide when launching the instances"
@@ -196,8 +203,15 @@ variable "min_size" {
 }
 
 variable "subnet_ids" {
+  type        = list(string)
   description = "A list of subnet IDs to launch resources in"
+  default     = null
+}
+
+variable "availability_zones" {
   type        = list(string)
+  description = "A list of Availability Zones where instances in the Auto Scaling group can be created. Used for launching into the default VPC subnet in each Availability Zone when not using the subnet_ids variable, or for attaching a network interface when an existing network interface ID is specified. Conflicts with subnet_ids."
+  default     = null
 }
 
 variable "default_cooldown" {