terraform apply from not generated resource - terraform

Question

I'm trying to create a list of maps from my list of subnet names so I've created the following:
created a variable named subnet_names of type list of strings
created a null resource block to create a list of maps from this list, like this:
resource "null_resource" "subnet_mapping" {
count = "${length(var.subnet_names)}"
triggers = {
name = "${element(var.subnet_names, count.index)}"
number = "${count.index}"
}
}
if I only execute this block I have my list of maps correctly but when I try to use this list of maps with a dynamic block this is not working.
resource "azurerm_virtual_network" "virtual_network" {
address_space = "${var.cidr_network_range}"
location = "${var.location}"
name = "${var.virtual_network_resource_name}"
resource_group_name = "${var.resource_group_name}"
count = "${length(var.subnet_names)}"
dynamic "subnet"{
for_each = [for s in null_resource.subnet_mapping: {
name = s.name
prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
}]
content {
name = subnet.value.name
address_prefix = subnet.value.prefix
}
}
depends_on = [null_resource.subnet_mapping]
}
resource "null_resource" "subnet_mapping" {
count = "${length(var.subnet_names)}"
triggers = {
name = "${element(var.subnet_names, count.index)}"
number = "${count.index}"
}
}
resource "azurerm_resource_group" "virtual_network_group" {
location = "${var.location}"
name = "${var.resource_group_name}"
}
it should be valid, but I still don't have the output of the null_resource so it fails
dynamic "subnet"{
for_each = [for s in null_resource.subnet_mapping: {
name = s.name
prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
}]
content {
name = subnet.value.name
address_prefix = subnet.value.prefix
}
}
depends_on = [null_resource.subnet_mapping]
}
my error message:
Error: Unsupported attribute
on main.tf line 10, in resource "azurerm_virtual_network" "virtual_network":
10: name = s.name
This object does not have an attribute named "name".
Error: Unsupported attribute
on main.tf line 10, in resource "azurerm_virtual_network" "virtual_network":
10: name = s.name
This object does not have an attribute named "name".
Error: Unsupported attribute
on main.tf line 10, in resource "azurerm_virtual_network" "virtual_network":
10: name = s.name
This object does not have an attribute named "name".
Error: Unsupported attribute
on main.tf line 10, in resource "azurerm_virtual_network" "virtual_network":
10: name = s.name
This object does not have an attribute named "name".
Error: Unsupported attribute
on main.tf line 11, in resource "azurerm_virtual_network" "virtual_network":
11: prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
This object does not have an attribute named "number".
Error: Unsupported attribute
on main.tf line 11, in resource "azurerm_virtual_network" "virtual_network":
11: prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
This object does not have an attribute named "number".
Error: Unsupported attribute
on main.tf line 11, in resource "azurerm_virtual_network" "virtual_network":
11: prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
This object does not have an attribute named "number".
Error: Unsupported attribute
on main.tf line 11, in resource "azurerm_virtual_network" "virtual_network":
11: prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,s.number)
This object does not have an attribute named "number".

Answer 1

From the message, I'm not clear how many Vnets do you want to create, because your code is a little confusing. For your issue with the null_resource, I don't think it's a good choice, I recommend the locals.
Here I assume you only want to create one Vnet with serial subnets and use a list to store the names of the subnets, then the example core code below:
locals {
subnets = [for sname in var.subnet_names: {
name = sname
# the index begin from 0, so you need to add 1
number = index(var.subnet_names, sname) + 1
}]
}
resource "azurerm_virtual_network" "virtual_network" {
address_space = "${var.cidr_network_range}"
location = "${var.location}"
name = "${var.virtual_network_resource_name}"
resource_group_name = "${var.resource_group_name}"
dynamic "subnet"{
for_each = [for s in local.subnets: {
name = s.name
prefix = cidrsubnet(var.cidr_network_range, 8 , s.number)
}]
content {
name = subnet.value.name
address_prefix = subnet.value.prefix
}
}
}

Answer 2

I solved this way, I've created a variable named
variable "subnets" {
type = list(map(string))
description = "A list of maps of names and network addresses bits for subnets that will be created inside this network (this is parallel to subnet_prefixes array)."
}
resource "azurerm_virtual_network" "virtual_network" {
address_space = var.cidr_network_range
location = var.location
name = var.virtual_network_resource_name
resource_group_name = var.resource_group_name
dynamic "subnet"{
for_each = [for subnet in var.subnets: {
name = subnet.name
prefix = cidrsubnet(element(var.cidr_network_range, 0),8 ,subnet.number)
}]
content {
name = subnet.value.name
address_prefix = subnet.value.prefix
}
}
}
resource "azurerm_resource_group" "virtual_network_group" {
location = var.location
name = var.resource_group_name
}
This way I already created the map, I would like to have created it automatically as I posted before but it seems to not be very common in terraform way.
In Charles Xu example the mapping will be created based on a sequence (1,2,3) and I would like to use it always in different ways like (21, 24, 26)
So the only solution I could find was to force the map before.
Anyway, thank you everyone