How to use Conditional Attributes in Terraform - terraform

Question

I wrote a script to create Azure VM using terraform. Script is flexible to take the OS as input. Now there are some attributes in azurerm_virtual_machine resource block which are specific to OS.
How to use a condition like if windows use os_profile_windows_config{} or if OS is linux use os_profile_linux_config{}.
Normal conditional statements didn't work as this attributes are not taking any values directly by using = .
resource "azurerm_virtual_machine" "vmdeploy" {
count = "${var.count_of_VMs}"
name = "${var.vm_name}-${count.index}"
resource_group_name = "${azurerm_resource_group.deployrg.name}"
availability_set_id = "${azurerm_availability_set.avset.id}"
location = "${azurerm_resource_group.deployrg.location}"
network_interface_ids = ["${element(azurerm_network_interface.nic.*.id, count.index)}"]
vm_size = "Standard_DS1_v2"
storage_image_reference{
publisher = "${var.OS_Image_Publisher}"
offer = "${var.OS_Image_Offer}"
sku = "${var.OS_Image_Sku}"
version = "latest"
}
storage_os_disk{
name = "${var.vm_name}-${count.index}-osdisk"
caching = "ReadWrite"
managed_disk_type = "Standard_LRS"
create_option = "FromImage"
}
storage_data_disk {
name = "${element(azurerm_managed_disk.mdisk.*.name, count.index)}"
managed_disk_id = "${element(azurerm_managed_disk.mdisk.*.id, count.index)}"
create_option = "Attach"
lun = 1
disk_size_gb = "${element(azurerm_managed_disk.mdisk.*.disk_size_gb, count.index)}"
}
os_profile {
computer_name = "${var.vm_name}-${count.index}"
admin_username = "XXXXXXXXXXXX"
admin_password = "XXXXXXXXXXXX"
}
os_profile_windows_config {
}
}
I am trying to find a way to use condition here to use respective config attribute based on OS version which is provided as input.

Answer 1

This is not possible pre terraform-0.12. This is possible with dynamic blocks in version 0.12.
provider "azurerm" {
version = "~>2.19.0"
features {}
}
variable "image" {
type = map
default = {
publisher = "Canonical"
offer = "UbuntuServer"
sku = "16.04-LTS"
version = "latest"
}
}
locals {
_is_microsoft = substr(lookup(var.image, "publisher", "value_not_declared"), 0, 9) == "Microsoft" ? true : false
is_linux = ! local._is_microsoft ? { empty = true } : {}
is_windows = local._is_microsoft ? { empty = true } : {}
}
resource "azurerm_resource_group" "rg" {
name = "rg"
location = "east us"
}
resource "azurerm_virtual_network" "rg" {
name = "-network"
address_space = ["10.0.0.0/16"]
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
}
resource "azurerm_subnet" "subnet" {
name = "subnet"
resource_group_name = azurerm_resource_group.rg.name
virtual_network_name = azurerm_virtual_network.rg.name
address_prefixes = ["10.10.10.0/24"]
}
resource "azurerm_network_interface" "rg" {
name = "nic"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
ip_configuration {
name = "ipconfig"
subnet_id = azurerm_subnet.subnet.id
private_ip_address_allocation = "Dynamic"
}
}
resource "azurerm_virtual_machine" "rg" {
name = "-vm"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
network_interface_ids = [azurerm_network_interface.rg.id]
vm_size = "Standard_D2_v3"
storage_image_reference {
publisher = lookup(var.image, "publisher")
offer = lookup(var.image, "offer")
sku = lookup(var.image, "sku")
version = lookup(var.image, "version")
}
storage_os_disk {
name = "disk1"
caching = "ReadWrite"
create_option = "FromImage"
managed_disk_type = "Standard_LRS"
}
os_profile {
computer_name = "computer"
admin_username = "localadmin"
admin_password = "donotuserthispassword123!"
}
dynamic "os_profile_linux_config" {
for_each = local.is_linux
content {
disable_password_authentication = false
}
}
dynamic "os_profile_windows_config" {
for_each = local.is_windows
content {
provision_vm_agent = true
}
}
}
Note the azurerm team decided this was not a
good
idea and split out the resources into two different types. Use
azurerm_linux_virtual_machine or azurerm_windows_virtual_machine.
Build a module with a single interface then use a count to pick which
resource to build either windows or linux.