I’ve got a custom module that I have created to build an Azure VM using azurerm_windows_virtual_machine and want to have a dynamic donditional block depending on if var.vm_image_custom_id is supplied.
If var.vm_image_custom_id is supplied, I want it to use ‘source_image_id’ if it isn’t I want to use a block ‘source_image_reference’ which is populated with publisher, offer etc.
Here is the code;
resource "azurerm_windows_virtual_machine" "main" {
tags = merge(var.tags)
enable_automatic_updates = "false"
name = upper("${var.vm_name}")
resource_group_name = data.azurerm_resource_group.main.name
location = data.azurerm_resource_group.main.location
license_type = var.license_type
size = var.vm_size
admin_username = var.vm_username
admin_password = var.vm_password
patch_mode = "Manual"
zone = var.vm_availability_zone
network_interface_ids = [
azurerm_network_interface.main.id,
]
os_disk {
caching = "ReadWrite"
storage_account_type = var.vm_os_disk_type
}
source_image_id = var.vm_image_custom_id != null ? var.vm_image_custom_id : null
dynamic "source_image_reference" {
for_each = var.vm_image_custom_id == null ? toset([1]) : toset([])
content {
publisher = var.vm_image_publisher
offer = var.vm_image_offer
sku = var.vm_image_sku
version = var.vm_image_version
}
}
It works if I supply an var.vm_image_custom_id but doesn’t if I don’t, this is the error I get;
It think my syntax is wrong but I can’t get my head around it 
Hi,
I noticed you are using toset() function in your for_each:
I think this might be the reason for your error, could you test it this way?
for_each = var.vm_image_custom_id == null ? [1] : []
Daniel
Yeah I tried that before using toSet but got the same error.
Does the syntax look right to you?
Yeah, it does.
Could you share here the four variables block you have in that dynamic block?
Yes of course, this is the variables.tf for the custom module
variable "vm_image_custom_id" {
description = "Specify a custom image instead of a market place image (Optional)"
default = null
}
variable "vm_image_publisher" {
description = "Market Place - The image publisher of the Virtual machine e.g. MicrosoftWindowsServer"
default = null
}
variable "vm_image_offer" {
description = "Market Place - The image offer of the Virtual machine e.g. WindowsServer"
default = null
}
variable "vm_image_sku" {
description = "Market Place - The image sku of the Virtual machine e.g. 2019-Datacenter"
default = null
}
Then I am calling the module from main.tf
module "corporate-servers" {
source = "../../modules/tf_azurerm_virtual_machine"
for_each = var.corporate-servers
rg_name = var.rg_name
vm_name = each.value["vm_name"]
license_type = var.license_type
data_subnet_name = each.value["data_subnet_name"]
data_vnet = var.data_vnet
data_vnet_rg = var.data_vnet_rg
vm_size = each.value["vm_size"]
vm_password = var.vm_admin_password
vm_availability_zone = each.value["vm_availability_zone"]
vm_image_publisher = var.vm_image_publisher
vm_image_offer = var.vm_image_offer
vm_image_sku = var.vm_image_sku
vm_image_custom_id = each.value["vm_image_custom_id"]
enable_accelerated_networking = var.enable_accelerated_networking
vm_require_data_disk = each.value["vm_require_data_disk"]
vm_data_disk_size = each.value["vm_data_disk_size"]
vm_ou_path = var.vm_ou_path
vm_add_to_domain_password = var.vm_domain_password
tags = var.common_tags
depends_on = [
azurerm_resource_group.main,
]
}
This is the terrafrom.tfvars
rg_name = "rg-corp-servers"
corporate-servers = {
SVR1 = {
vm_name = "SVR1"
data_subnet_name = "subnet-common"
vm_availability_zone = "1"
vm_size = "Standard_B2ms"
vm_require_data_disk = false
vm_data_disk_size = null
vm_image_custom_id = "/subscriptions/xxxxsubscriptionidxxxx/resourceGroups/rg-image/providers/Microsoft.Compute/images/live-server-image"
}
SVR2 = {
vm_name = "SVR2"
data_subnet_name = "subnet-common"
vm_availability_zone = "1"
vm_size = "Standard_D4s_v3"
vm_require_data_disk = true
vm_data_disk_size = "1024"
vm_image_publisher = "MicrosoftWindowsServer"
vm_image_offer = "WindowsServer"
vm_image_sku = "2019-Datacenter"
vm_image_custom_id = null
}
}
Thanks again for your help with this!
Don’t you have variables.tf for root level in your code?
