if clauses in terraform 0.12 - azure

Question

I am new to Terraform, using Azure...I am trying to build a module "compute" where I can deploy a single vm or a vm set.
For a single VM I need a network interface, a security group association, and a azurerm_linux_virtual_machine. For a vm set I need to provision only azurerm_linux_virtual_machine_scale_set. Is it possible to pass a boolean variable to this module to select which resources get executed?
I've checked this post but apparently there is no such thing.
Should I simply divide the module into compute/vm and compute/scale_set and actually have two modules, one for single vms and one for vm sets? Not sure if this will be a pain to maintain in the future.

Answer 1

Yes, you can use a boolean to select what is built. Generally speaking, you can use the count control:
resource "azurerm_linux_virtual_machine" "vm" {
count = var.single_only ? 1 : 0
... (rest of config)
}
resource "azurerm_linux_virtual_machine_scale_set" "vm_set" {
count = var.single_only ? 0 : 1
... (rest of config)
}
(see the end of this section on count resources)

Answer 2

Yes, it's possible and you don't need to divide the module.
As the statements in the posted link:
You can accomplish the resource creating selection by using the count parameter and conditional expression.
In this case, you can declare two bool variables like this:
variable "create_vm" {
description = "If set to true, it will create vm"
type = bool
}
variable "create_vmss" {
description = "If set to true, it will create vmss"
type = bool
}
and define the resource azurerm_linux_virtual_machine and azurerm_linux_virtual_machine_scale_set in the same VM module.
resource "azurerm_linux_virtual_machine" "example" {
count = var.create_vm ? 1 : 0
name = "example-machine"
resource_group_name = azurerm_resource_group.example.name
location = azurerm_resource_group.example.location
size = "Standard_F2"
...
resource "azurerm_linux_virtual_machine_scale_set" "example" {
count = var.create_vmss ? 1 : 0
name = "example-vmss"
resource_group_name = azurerm_resource_group.example.name
location = azurerm_resource_group.example.location
sku = "Standard_F2"
instances = 1
admin_username = "adminuser"
....
Then call the submodule like this,
module "vm" {
source = "./modules/vm"
create_vm = true
create_vmss = false
...
}
Hope this helps.