Dynamic network interface for Compute Instance module - google-cloud-platform

Question

We've Terraform module that creates compute_instance.
Some instances should get public IP.
Public IP created when you define "access_config {}" property under network_interface:
network_interface {
network = "default"
access_config {
}
}
We try to inject dynamically the network interface and the access_config from
"production/Main.tf" that called to this module:
module "arbiter" {
source = "../modules/compute"
name = "arbiter"
machine_type = "custom-1-2048"
zones = ["europe-west2-a"]
tags = ["mongo-db"]
metadata = {
sshKeys = "${var.ssh_user}:${file("ssh-keys/main.rsa.pub")}"
}
network_interface = { -> this line is worng
network = "default"
}
}
How can we inject a dynamic object to network_interface property?
Is it possible with Terraform if not, What are the alternatives?

Answer 1

In your arbiter module do this:
variable "external_ip" {
description = "Controls if VM gets external IP"
default = false
}
locals {
access_config = {
"0" = []
"1" = [{}]
}
}
resource "google_compute_instance" "arbiter" {
name = "${var.name}"
machine_type = "${var.type}"
zone = "${var.zones}"
tags = "${var.tags}"
metadata = "${var.metadata}"
boot_disk {
initialize_params {
image = "some/image"
}
}
network_interface {
network = "default"
access_config = "${local.access_config[var.external_ip]}"
}
}
Then, when using the module, you can specify external_ip variable to indicate that VM should be accessible from the internet.
module "arbiter" {
source = "../modules/compute"
name = "arbiter"
machine_type = "custom-1-2048"
zones = ["europe-west2-a"]
tags = ["mongo-db"]
metadata = {
sshKeys = "${var.ssh_user}:${file("ssh-keys/main.rsa.pub")}"
}
external_ip = true
}
More details about Terraform and null values tricks: Null values in Terraform v0.11.x