How to get value from module in another module - Terraform (Azure) - azure

Question

Im trying to get value from one module and use it in another module.
I have module - vnet
resource "azurerm_virtual_network" "vnet" {
name = var.vnet_name
resource_group_name = var.resource_group_name
location = var.location
address_space = var.address_space
}
resource "azurerm_subnet" "subnet" {
name = "${var.vnet_name}-subnet"
resource_group_name = var.resource_group_name
virtual_network_name = azurerm_virtual_network.vnet.name
address_prefixes = var.subnet_prefixes
}
and the output is :
output "subnet_id" {
value = "${azurerm_subnet.subnet.id}"
}
output "vnet_name" {
value = "${azurerm_virtual_network.vnet.name}"
}
from this module i would like to get the vnet name and the subnet id for my other module that im using to create a nic.
nic module
module "vnet" {
source = "../vnet"
}
resource "azurerm_network_interface" "nic" {
name = "${module.vnet.vnet_name}-nic"
location = "east us 2"
resource_group_name = "null"
ip_configuration {
name = " "
subnet_id = module.vnet.subnet_id
private_ip_address_allocation = "Dynamic"
}
}
this way is working BUT the terraform plan , planning to create 2 resource per each resource because the way im using to get the values .
under nic module im using again the vnet module so its will create second vnet.
my main.tf is
resource "azurerm_resource_group" "rg" {
name = var.resource_group.name
location = var.resource_group.location
}
module "ib151w-vnet" {
source = "./modules/vnet"
resource_group_name = azurerm_resource_group.rg.name
vnet_name = "ib151w-vnet"
address_space = var.address_space
subnet_prefixes = var.subnet_prefixes
}
module "ib151w-nic" {
source = "./modules/nic"
name = "nic-test-123"
location = "east us 2"
resource_group_name = "ib151w"
}
the question is how can i get the vnet name and subnet id to use inside the nic module ?
i know there is alot of better ways to establish my request but im
just learning terraform and trying this specific way :)

Answer 1

how can i get the vnet name and subnet id to use inside the nic module
You have to explicitly pass those values in the root module:
module "ib151w-nic" {
source = "./modules/nic"
name = "nic-test-123"
location = "east us 2"
resource_group_name = "ib151w"
vnet_name = module.vnet.vnet_name
subnet_id = module.vnet.subnet_id
}
Also you have to modify your vnet module to make vnets and subents conditional. For example, add variable in the vent module:
variable "should_create_vnet_and_subnet" {
default = true
}
then make the resource conditional:
resource "azurerm_virtual_network" "vnet" {
count = should_create_vnet_and_subnet == true ? 1 : 0
name = var.vnet_name
resource_group_name = var.resource_group_name
location = var.location
address_space = var.address_space
}
resource "azurerm_subnet" "subnet" {
count = should_create_vnet_and_subnet == true ? 1 : 0
name = "${var.vnet_name}-subnet"
resource_group_name = var.resource_group_name
virtual_network_name = azurerm_virtual_network.vnet.name
address_prefixes = var.subnet_prefixes
}
And the rest. Basically you have to rewrite your entire vnet module around conditional resources.

Answer 2

There are a lot of things to reconsider here but I would like to stick to your query only as you have requested.
How to get value from the module in another module - Terraform
As I can see you are already using two modules for vnet(which includes subnet) and nic and also using two modules interface calls to use them. You can simply use variables in your nic module and then at the interface level you can pass the outputs from vnet module as an attribute to your nic module.
Refer to the below code.
# main.tf or MODULE INTERFACES
## Default variables ##
variable "resource_group_name" {
type = string
description = "(optional) resource group name in which resources will created"
default = "stack-over-flow-query"
}
variable "location" {
type = string
description = "(optional) location where resources would be created."
default = "east us 2"
}
################################
resource "azurerm_resource_group" "rg" {
name = var.resource_group_name
location = var.location
}
module "ib151w-vnet" {
source = "./modules/vnet"
resource_group_name = azurerm_resource_group.rg.name
location = azurerm_resource_group.rg.location
vnet_name = "ib151w-vnet"
address_space = ["10.0.0.0/16"]
subnet_prefixes = ["10.0.1.0/24"]
}
module "ib151w-nic" {
source = "./modules/nic"
name = "${module.ib151w-vnet.vnet_name}-nic-test-123"
location = azurerm_resource_group.rg.location
resource_group_name = azurerm_resource_group.rg.name
subnet_id = module.ib151w-vnet.subnet_id
ip_configuration = "stackoverflow"
}
## NIC Module
resource "azurerm_network_interface" "nic" {
name = var.name
location = var.location
resource_group_name = var.resource_group_name
ip_configuration {
name = var.ip_configuration
subnet_id = var.subnet_id
private_ip_address_allocation = var.private_ip_address_allocation
}
}
## Required variable definitions with defaults(best practice installation in your situation)
Using the same outputs as yours in the vnet module.
output "vnet_name" {
value = azurerm_virtual_network.vnet.name
}
output "subnet_id" {
value = azurerm_subnet.subnet.id
}
Note: "${}"aka interpolation is not required when using terraform referencing without variables or any unknown value to terraform.
There can be a lot more ways to have a module like this but I would suggest at least a few things to try and do hands-on.
Use looping in your module to make multiple resources with one interface call [ only when necessary and make sense ]
https://developer.hashicorp.com/terraform/tutorials/configuration-language/for-each
Warning: extra looping can increase complexity.
Use conditions to control your module behavior.
https://developer.hashicorp.com/terraform/language/expressions/conditionals
And the most important when to use a module.
https://developer.hashicorp.com/terraform/language/modules/develop#when-to-write-a-module
I hope this helps and as I have stated this only answers your query, not some best practices or best vnet-nic module.