Terraform: How to iterate the name or another variable in a resource group when the variable being passed in is a list of a list of maps?

Question

This is what I have so far, while I can pull a specific list or name using the local variables, I am having trouble transitioning this into the resource group. First, am I attempting this the right way? If not how can I iterate on the name for the subnet so that the subnets belonging to the respective vnet map are added?

 variable "vnets" { default = [ { vnet_name = "test-vnet" address_space = "10.250.0.0" network_size = 16 subnets = [ { name = "first-subnet" network_security_group = "first-nsg" security_group_rules = [ { name = "first-sg" priority = 100 } ] }, { name = "second-subnet" network_security_group = "second-nsg" security_group_rules = [ { name = "second-sg" priority = 100 } ] } ] } ] } locals { subnet_names = { for vnet in var.vnets[*]: (vnet.vnet_name) => vnet.subnets[*].name } security_group_names = flatten(var.vnets[*].subnets[*].security_group_rules[*].name) } resource "azurerm_subnet" "subnets" { count = length(var.vnets) #??? name = locals.subnet_names[count.index].subnets.name resource_group_name = data.azurerm_resource_group.network_group.name virtual_network_name = azurerm_virtual_network.vnets.*.name address_prefixes = ["10.0.1.0/24"] }

Answer 1

I think the easiest would be to flatten your subnet_names :

locals {
   
   subnet_names = { 
         for vnet in var.vnets[*]:
           (vnet.vnet_name) =>  vnet.subnets[*].name
   }
   
   security_group_names = flatten(var.vnets[*].subnets[*].security_group_rules[*].name)
   

   # uniqueness of "${vnet}-${subnet}" pairs is assumed. it will not work
   # if the pairs are not unique
   subnet_names_flat = merge([
         for vnet, subnets in local.subnet_names:
           {
             for subnet in subnets:          
               "${vnet}-${subnet}" => {name = vnet, subnet = subnet}
           }
         ]...)
     
}

Which will result in subnet_names_flat being:

{
  "test-vnet-first-subnet" = {
    "name" = "test-vnet"
    "subnet" = "first-subnet"
  }
  "test-vnet-second-subnet" = {
    "name" = "test-vnet"
    "subnet" = "second-subnet"
  }
}

Then your azurerm_subnet.subnets could as below. However, I'm not able to verify correctness of your the azurerm_subnet , thus you may need to change it further. But the idea is to iterate over local.subnet_names_flat , which makes the for_each very easy to use:

resource "azurerm_subnet" "subnets" {

  for_each                 = local.subnet_names_flat
  
  name                      = each.value.subnet  
  resource_group_name       = data.azurerm_resource_group.network_group.name
  virtual_network_name      = each.value.vnet
  address_prefixes          = ["10.0.1.0/24"]
}