Question 170006 in Azure Question posted in
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Can I leave some values out when mapping an object in Terraform with Azure?

  • if I don’t want to provide route table for all the subnets in the virtual
    network then what should I used here because if I run without route
    table then I am getting error. route table id is required in subnet2.
│ Missing required argument
│
│ with module.virtual_network["test-vnet"].azurerm_subnet_route_table_association.route-link-subnet["subnet2"],
│ on modulesvirtualNetworkmain.tf line 30, in resource "azurerm_subnet_route_table_association" "route-link-subnet":
│ 30: route_table_id = each.value.route_table
│
│ The argument "route_table_id" is required, but no definition was found.

i am creating here multiple virtual network with multiple subnets on each vnet.

variable "networks" {
      type = map(object({
        resource_group_name = string
        location            = string
        addressSpace        = list(string)
        dnsServers          = optional(list(string))
        subnets = map(object({
          addressPrefix                     = string
          privateEndpointNetworkPolicies    = optional(bool)
          privateLinkServiceNetworkPolicies = optional(bool)
          service_endpoints                 = optional(list(string))
          route_table                       = optional(string)
        }))
      }))
    }


networks = {
  test-vnet = {
    resource_group_name = "testrg"
    location            = "eastus"
    addressSpace        = ["10.229.192.0/20"]
    dnsServers          = ["10.231.18.4"]
    subnets = {
      subnet1 = {
        addressPrefix = "10.229.199.0/24"
        networkSecurityGroups = {
          subnet1-nsg = {
            security_rules = []
          }
        }
        route_table = "/subscriptions//resourceGroups/test-rg/providers/Microsoft.Network/routeTables/test-rt"
      }
      subnet2 = {
        addressPrefix                     = "10.229.198.0/24"
        privateEndpointNetworkPolicies    = true
        privateLinkServiceNetworkPolicies = true
        service_endpoints = [
          "Microsoft.Storage"
        ]
        networkSecurityGroups = {
          subnet2-nsg = {
            security_rules = []
          }
        }
      }
    }
  }


resource "azurerm_subnet_route_table_association" "route-link-subnet" {
  for_each       = var.subnets
  subnet_id      = module.subnets[each.key].subnet_id
  route_table_id = each.value.route_table
  depends_on = [
    module.subnets,
    azurerm_virtual_network.Virtual_Network
  ]
}
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2

Answers


  1. 0

    You have to provide route_table for subnet2 in your var.subnets.

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  2. 0

    Your input variable’s type constraint disagrees with the requirements of azurerm_subnet_route_table_association: the route_table_id argument is required for that resource, so it isn’t valid to assign null to it.

    If you wish to only declare route table associations for subnets that have a non-null route_table_id then you can use a for expression with an if clause to filter the var.subnets value to include only the elements that have route table IDs:

    resource "azurerm_subnet_route_table_association" "route-link-subnet" {
  for_each = tomap({
    for k, s in var.subnets : k => s
    if s.route_table != null
  })

  subnet_id      = module.subnets[each.key].subnet_id
  route_table_id = each.value.route_table

  depends_on = [
    azurerm_virtual_network.Virtual_Network
  ]
}

    With the example above the for_each map will only include the subnets that have route_table set, and so there will be no resource instance declared at all for the ones that do not have route tables.

    Note that this strategy will only be effective if the route_table attribute is always known during the plan phase of Terraform, because otherwise Terraform won’t be able to decide during planning how many instances of this resource are declared. What you showed in your question would work, where the route table ID is hard-coded into your object, but it would not work if the route table ID were derived from another resource block whose remote object hasn’t been created yet.

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