Terraform using random provider with count in module - terraform

Question

I am having child module for Windows virtual machine.
Then I have root module (main.tf file), where I am using that child module
module "vm-win-resource" {
source = "./Modules/ServerWindows"
count = 2
vm-name = "vm-win-${random_string.rnd.result}" #OR "vm-win-${module.rnd-num.rnd-result}"
vm-rg = module.rg-resouce.rg-name
vm-location = module.rg-resouce.rg-location
nic-name = "vm-win-${random_string.rnd.result}-nic1" #OR "vm-win-${module.rnd-num.rnd-result}-nic1"
nic-rg = module.rg-resouce.rg-name
nic-location = module.rg-resouce.rg-location
nic-ip-subnet = "HERE IS SUBNET ID"
}
In same main.tf file, if I use random_string provider directly
resource "random_string" "rnd" {
length = 4
min_numeric = 4
special = false
lower = true
}
or if I create module, for random number and use it in module for virtual machine, result is same.
module "rnd-num" {
source = "./Modules/RandomNumber"
}
I get same name (generated number for both)
+ vm-win-name = [
+ [
+ "vm-win-6286",
+ "vm-win-6286",
],
]
So in both cases, value is generated only once.
Question is how can I generate random number for every loop in module for virtual machine?
Thank you for any help!
UPDATE
As workaround, I have placed provider to generate random number into virtual machine resource/module specification
resource "azurerm_windows_virtual_machine" "vm-resource" {
name = "${var.vm-name}-${random_string.rnd.result}"
resource_group_name = var.vm-rg
location = var.vm-location
size = var.vm-size
admin_username = var.vm-admin
admin_password = var.vm-adminpwd
network_interface_ids = [
azurerm_network_interface.nic-resource.id,
]
os_disk {
caching = "ReadWrite"
storage_account_type = var.vm-os-disk-type
}
source_image_reference {
publisher = var.vm-os-image.publisher
offer = var.vm-os-image.offer
sku = var.vm-os-image.sku
version = var.vm-os-image.version
}
tags = var.resource-tags
}
resource "random_string" "rnd" {
length = 4
min_numeric = 4
special = false
lower = true
}
it does the job but I would prefer to use it in main.tf file and not directly in resource/module specification, if it is possible.

Answer 1

A few words about how Terraform random_string works:
random_string generates a random string from specific characters. This string is generated once. Referencing its result attribute in multiple places will provide you the same output. Using it as random_string.rnd.result will not act as a function call, this means that it will provide the same value in every place.
The result value of a random_string will not change after consecutive applies. This is obvious, if we think about it. If it would change, the usage of random_string would be dangerous, since it would result in re-provisioning the resources which are referencing it.
If we want to have multiple different random strings, we have to define multiple random_string resources. For example:
resource "random_string" "rnd" {
count = 2
length = 4
min_numeric = 4
special = false
lower = true
}
module "vm-win-resource" {
source = "./Modules/ServerWindows"
count = 2
vm-name = "vm-win-${random_string.rnd[count.index].result}"
vm-rg = module.rg-resouce.rg-name
vm-location = module.rg-resouce.rg-location
nic-name = "vm-win-${random_string.rnd[count.index].result}-nic1"
nic-rg = module.rg-resouce.rg-name
nic-location = module.rg-resouce.rg-location
nic-ip-subnet = "HERE IS SUBNET ID"
}
Please note, we are using a count for the random_string resource as well.