terraform module depends_on

This is a workaround for hashicorp/terraform#10462 to make terraform modules work like resources depends_on

demo

With following main.tf

provider "google" {}

module "ip_address_1" {
  source = "./modules/ip_address"

  name = "first"
}

module "ip_address_2" {
  source = "./modules/ip_address"
  # list all dependencies here
  depends_list = [module.ip_address_1.depend_on]

  name = "second"
}

Modules (resources) are created after each other:

GOOGLE_PROJECT=my-project GOOGLE_REGION=europe-north1  terraform apply -auto-approve
module.ip_address_1.google_compute_address.default: Creating...
module.ip_address_1.google_compute_address.default: Creation complete after 4s [id=projects/my-project/regions/europe-north1/addresses/first]
module.ip_address_2.google_compute_address.default: Creating...
module.ip_address_2.google_compute_address.default: Creation complete after 4s [id=projects/my-project/regions/europe-north1/addresses/second]

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Every module needs to be written like this:

# -- workaround
variable "depends_list" {
  default = []
}

output "depend_on" {
  # list all resources in this module here so that other modules are able to depend on this
  value = [google_compute_address.default.id]
}

# -- actual module
variable "name" {}
resource "google_compute_address" "default" {
  # set this for every resource created in this module so that creation blocks until the dependencies have been created
  depends_on = [var.depends_list]

  name = var.name
}