How do I assign random subnet_id into azurerm_network_interface?

Question

### variable
variable "vm-subnets" { 
  type = list(string) 
  default = ["7.0.1.0/24","7.0.2.0/24","7.0.3.0/24"] 
}

### subnet
resource "azurerm_subnet" "task_subnet" {
  name                 = "subnet-${format("%02d",count.index)}"
  resource_group_name  = azurerm_resource_group.task.name
  virtual_network_name = azurerm_virtual_network.task_vnet.name
  network_security_group_id = azurerm_network_security_group.task_nsg.id
  address_prefix       = var.vm-subnets[count.index]
  count                 = length(var.vm-subnets)
}

### NIC
resource "azurerm_network_interface" "vm_nic" {
  name                = "nic--${format("%02d",count.index)}"
  location            = var.region
  resource_group_name = azurerm_resource_group.task.name
  count               = var.vm-count

  ip_configuration {
    name                          = "${var.resource_prefix}-${format("%02d",count.index)}-ip"
    subnet_id                     = azurerm_subnet.task_subnet.*.id[count.index]
    private_ip_address_allocation = "dynamic"
    public_ip_address_id          = azurerm_public_ip.task_public_ip.*.id[count.index]
  }<br>
}

I need to 7 VM into 3 subnet for like subnet-A = 2VMs ,subnet-B=2VMs, subnet-C = 3VMs or randomly `` ERROR: Error: Invalid index

on vm-network.tf line 11, in resource "azurerm_network_interface" "vm_nic": 11: subnet_id = azurerm_subnet.task_subnet.*.id[count.index] |---------------- | azurerm_subnet.task_subnet is tuple with 3 elements | count.index is 4

The given key does not identify an element in this collection value.

Error: Invalid index

on vm-network.tf line 11, in resource "azurerm_network_interface" "vm_nic": 11: subnet_id = azurerm_subnet.task_subnet.*.id[count.index] |---------------- | azurerm_subnet.task_subnet is tuple with 3 elements | count.index is 3

The given key does not identify an element in this collection value.



What modification can be done to resolve it and how can I assign different/random subnet on each vm rather then count loop.

I also try to do it using random_shuffle and set-product function but not get the desired output .. please Help 

Answer 1

After 2 days of logical struggle i finally able to find a solution or the questions that I create : USING element function https://www.terraform.io/docs/configuration/functions/element.html

NIC

resource "azurerm_network_interface" "vm_nic" {
  name                = "nic--${format("%02d",count.index)}"
  location            = var.region
  resource_group_name = azurerm_resource_group.task.name
  count               = var.vm-count
  ip_configuration {
    name                          = "${var.resource_prefix}-${format("%02d",count.index)}-ip"
    subnet_id                     =  element(azurerm_subnet.task_subnet.*.id, count.index)
    private_ip_address_allocation = "dynamic"
    public_ip_address_id          = azurerm_public_ip.task_public_ip.*.id[count.index]
  }
} 

subnet_id =  element(azurerm_subnet.task_subnet.*.id, count.index)

using element function ["7.0.1.0/24","7.0.2.0/24","7.0.3.0/24"] at vm count.index = 3 it goes back to subnet index = 0 so that how it works and tested it at vm.count = 5, 7 , 10. ✌🏻