How to build a VM in GCP with a secondary alias IP. Assuming that you already have a compute and a local block in your Terraform file.

Go to the locals block and add the local variables you’ll need.

locals {
  project          = "projectId"
  hostname         = "yourhostname"

Reserve an internal ip address by adding the google_compute_address block to your Terraform file.

resource "google_compute_address" "alias-ip" {
  name = "${local.hostname}-alias-ip"
  region = "us-central1"
  address_type = "INTERNAL"
  subnetwork = local.subnetwork

Inside your existing compute instance block, add the alias_ip_range to the network interface block.

  network_interface {
    network    =
    subnetwork = local.subnetwork
    alias_ip_range {
      ip_cidr_range = google_compute_address.alias-ip.address

The script will reserve an internal ip address and attach it the vm as an alias ip.