Using local variables for custom functions

In the Manipulating variables recipe in this chapter, we learned how to use variables to dynamize our Terraform configuration. Sometimes, this can be a bit tedious when it comes to using combinations of variables.

In this recipe, we will learn how to implement local variables and use them as custom functions.

Getting ready

To start with, we will use the following Terraform configuration:

variable "application_name" {
  description = "The name of application"
}
variable "environment_name" {
  description = "The name of environment"
}
variable "country_code" {
  description = "The country code (FR-US-...)"
}
resource "azurerm_resource_group" "rg" {
  name = "XXXX" # VARIABLE TO USE
  location = "West Europe"
}
resource "azurerm_public_ip" "pip" {
  name = "XXXX" # VARIABLE TO USE
  location = "West Europe"
  resource_group_name = azurerm_resource_group.rg.name
  allocation_method = "Dynamic"
  domain_name_label = "mydomain"
}

The goal of this recipe is to consistently render the names of the Azure resources. We must provide them with the following nomenclature rule:

CodeAzureResource - Name Application - Environment name - Country Code

The source code of this recipe is available at https://github.com/PacktPublishing/Terraform-Cookbook-Second-Edition/tree/main/CHAP02/localvariables.

How to do it…

Follow these steps:

1. In the main.tf file, which contains our Terraform configuration, we will add a local variable called resource_name, along with the following code:

   locals {
     resource_name = "${var.application_name}-${var.environment_name}-${var.country_code}"
   }
   

2. We then use this local variable in the resources with the following code:

   resource "azurerm_resource_group" "rg" {
    name = "RG-${local.resource_name}"
    location = "westeurope"
   }
   resource "azurerm_public_ip" "pip" {
    name = "IP-${local.resource_name}"
    location = "westeurope"
    resource_group_name = azurerm_resource_group.rg.name
    allocation_method = "Dynamic"
    domain_name_label = "mydomain"
   }
   

How it works…

In Step 1, we created a variable called resource_name that is local to our Terraform configuration. This allows us to create a combination of several Terraform variables (which we will see the result of in the Using outputs to expose Terraform provisioned data recipe of this chapter).

Then, in Step 2, we used this local variable with the local.<name of the local variable> expression. Moreover, in the name property, we used it as a concatenation of a variable and static text, which is why we used the "${}" syntax.

The result of executing this Terraform configuration is as follows:

Figure 2.9: Using the locals variable

In the previous screenshot, we can see the output of executing the terraform plan command with the name of the resource group that we calculated with the locals variable.

There’s more…

The difference between a local variable and Terraform variable is that the local variable can’t be redefined in the Terraform variables file (tfvars), with environment variables, or with the -var CLI argument.

See also

• For more information on local block, look at the following documentation: https://www.terraform.io/docs/configuration/locals.html.
• The Terraform locals learning lab is available at https://learn.hashicorp.com/tutorials/terraform/locals.