Terraform for_each if value exists in object - terraform

Question

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.

Answer 1

Based on your scenario, I'm guessing vnet_spoke_object in input looks like this:
vnet_spoke_object = {
specialsubnets = {
subnetA = {
cidr = "..."
}
subnetB = {
cidr = "..."
route = "..."
}
}
}
The problem with that is that a missing route entry doesn't resolve to null, it causes a panic or crash. You'd need to write your input like this (with explicit nulls):
vnet_spoke_object = {
specialsubnets = {
subnetA = {
cidr = "..."
route = null
}
subnetB = {
cidr = "..."
route = "..."
}
}
}
Or lookup route by name and provide a null default in your for map generator expression like this:
for_each = {
for key, value in var.vnet_spoke_object.specialsubnets:
key => value
if lookup(value, "route", null) != null
}