Terraform for_each if value exists in object

Terraform
1

I would like to dynamically create some subnets and route tables from a .tfvars file, and then link each subnet to the associated route table if specified.

Here is my .tfvars file:

vnet_spoke_object                      = {
    specialsubnets                     = {
        Subnet_1                       = {
            name                       = "test1"
            cidr                       = ["10.0.0.0/28"]
            route                      = "route1"
        }
        Subnet_2                       = {
            name                       = "test2"
            cidr                       = ["10.0.0.16/28"]
            route                      = "route2"
        }
        Subnet_3                       = {
            name                       = "test3"
            cidr                       = ["10.0.0.32/28"]
        }
    }
}

route_table                            = {
    route1                             = {
        name                           = "route1"
        disable_bgp_route_propagation  = true
        route_entries                  = {
            re1                        = {
                name                   = "rt-rfc-10-28"
                prefix                 = "10.0.0.0/28"
                next_hop_type          = "VirtualAppliance"
                next_hop_in_ip_address = "10.0.0.10"
            }
        }
    }
    route2                             = {
        name                           = "route2"
        disable_bgp_route_propagation  = true
        route_entries                  = {
            re1                        = {
                name                   = "rt-rfc-10-28"
                prefix                 = "10.0.0.16/28"
                next_hop_type          = "VirtualAppliance"
                next_hop_in_ip_address = "10.0.0.10"
            }
        }
    }
}

…and here is my build script:

provider "azurerm" {
    version                        = "2.18.0"
    features{}
}

variable "ARM_LOCATION" {
    default                        = "uksouth"
}

variable "ARM_SUBSCRIPTION_ID" {
    default                        = "asdf-b31e023c78b8"
}

variable "vnet_spoke_object" {}
variable "route_table" {}

module "names" {
    source                         = "./nbs-azure-naming-standard"
    env                            = "dev"
    location                       = var.ARM_LOCATION
    subId                          = var.ARM_SUBSCRIPTION_ID
}

resource "azurerm_resource_group" "test" {
    name                           = "${module.names.standard["resource-group"]}-vnet"
    location                       = var.ARM_LOCATION
}

resource "azurerm_virtual_network" "test" {
    name                           = "${module.names.standard["virtual-network"]}-test"
    location                       = var.ARM_LOCATION
    resource_group_name            = azurerm_resource_group.test.name
    address_space                  = ["10.0.0.0/16"]
}

resource "azurerm_subnet" "test" {
    for_each                       = var.vnet_spoke_object.specialsubnets
    name                           = "${module.names.standard["subnet"]}-${each.value.name}"
    resource_group_name            = azurerm_resource_group.test.name
    virtual_network_name           = azurerm_virtual_network.test.name
    address_prefixes               = each.value.cidr
}

resource "azurerm_route_table" "test" {
    for_each                       = var.route_table
    name                           = "${module.names.standard["route-table"]}-${each.value.name}"
    location                       = var.ARM_LOCATION
    resource_group_name            = azurerm_resource_group.test.name
    disable_bgp_route_propagation  = each.value.disable_bgp_route_propagation
    dynamic "route" {
        for_each                   = each.value.route_entries
        content {
            name                   = route.value.name
            address_prefix         = route.value.prefix
            next_hop_type          = route.value.next_hop_type
            next_hop_in_ip_address = contains(keys(route.value), "next_hop_in_ip_address") ? route.value.next_hop_in_ip_address: null
        }
    }
}

That part works fine in creating the vnet/subnet/route resources, but the problem I face is to dynamically link each subnet to the route table listed in the .tfvars. Not all the subnets will have a route table associated with it, thus it will need to only run IF the key/value route is listed.

resource "azurerm_subnet_route_table_association" "test" {
    for_each                       = {
        for key, value in var.vnet_spoke_object.specialsubnets:
            key => value
            if value.route != null
    }

    lifecycle {
        ignore_changes             = [
            subnet_id
        ]
    }
    subnet_id                      = azurerm_subnet.test[each.key].id
    route_table_id                 = azurerm_route_table.test[each.key].id
}

The error I face with the above code is:

Error: Unsupported attribute

  on main.tf line 65, in resource "azurerm_subnet_route_table_association" "test":
  65:             if value.route != null

This object does not have an attribute named "route".

I have tried various ways with no success, and I’m at a loss here and would appreciate any guidance posisble.

2

try() or can() should work.

eg

 [...]
for_each                       = {
        for key, value in var.vnet_spoke_object.specialsubnets:
            key => value
            if try(value.route, null) != null
    }

or

[...]
for_each                       = {
        for key, value in var.vnet_spoke_object.specialsubnets:
            key => value
            if can(value.route)
    }
3

It turns out that i need to actually have a value as null in the .tfvars code. TF doesn’t understand null as nothing, but as an actual value

route                      = null