Simplify Terraform configuration with locals

10min
|
Terraform

Terraform local values (or "locals") assign a name to an expression or value. Using locals simplifies your Terraform configuration – since you can reference the local multiple times, you reduce duplication in your code. Locals can also help you write more readable configuration by using meaningful names rather than hard-coding values.

Unlike variables found in programming languages, Terraform's locals do not change values during or between Terraform runs such as plan, apply, or destroy. You can use locals to give a name to the result of any Terraform expression, and re-use that name throughout your configuration. Unlike input variables, locals are not set directly by users of your configuration.

In this tutorial, you will use Terraform to deploy a web application on AWS. The supporting infrastructure includes a VPC, load balancer, and EC2 instances. You will then use local values to reduce repetition in the configuration, and then combine local values with input variables to require a minimal set of resource tags while still allowing for user customization.

Prerequisites

You can complete this tutorial using the same workflow with either Terraform Community Edition or HCP Terraform. HCP Terraform is a platform that you can use to manage and execute your Terraform projects. It includes features like remote state and execution, structured plan output, workspace resource summaries, and more.

Select the HCP Terraform tab to complete this tutorial using HCP Terraform.

This tutorial assumes that you are familiar with the Terraform workflow. If you are new to Terraform, complete the Get Started tutorials first.

In order to complete this tutorial, you will need the following:

Terraform v1.1+ installed locally.
An AWS account with local credentials configured for use with Terraform.

This tutorial assumes that you are familiar with the Terraform and HCP Terraform workflows. If you are new to Terraform, complete the Get Started tutorials first. If you are new to HCP Terraform, complete the HCP Terraform Get Started tutorials first.

In order to complete this tutorial, you will need the following:

Terraform v1.1+ installed locally.
An AWS account.
An HCP Terraform account with HCP Terraform locally authenticated.
An HCP Terraform variable set configured with your AWS credentials.

Note

Some of the infrastructure in this tutorial may not qualify for the AWS free tier. Destroy the infrastructure at the end of the guide to avoid unnecessary charges. We are not responsible for any charges that you incur.

Clone example repository

Clone the example repository for this tutorial. The configuration in this repository defines a web application, VPC, load balancer, and EC2 instances.

$ git clone https://github.com/hashicorp-education/learn-terraform-locals

Change to the repository directory.

$ cd learn-terraform-locals

Create infrastructure

Initialize this configuration.

$ terraform init
Initializing the backend...
##...

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

Open your terraform.tf file and uncomment the cloud block. Replace the organization name with your own HCP Terraform organization.

terraform.tf

terraform {
  cloud {
    organization = "organization-name"
    workspaces {
      name = "learn-terraform-locals"
    }
  }

  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.4.0"
    }
  }

  required_version = ">= 1.1"
}

Initialize your configuration. Terraform will automatically create the learn-terraform-locals workspace in your HCP Terraform organization.

$ terraform init
Initializing HCP Terraform...
Initializing provider plugins...
- Reusing previous version of hashicorp/aws from the dependency lock file
- Installing hashicorp/aws v4.4.0...
- Installed hashicorp/aws v4.4.0 (signed by HashiCorp)
HCP Terraform has been successfully initialized!
You may now begin working with HCP Terraform. Try running "terraform plan" to
see any changes that are required for your infrastructure.
If you ever set or change modules or Terraform Settings, run "terraform init"
again to reinitialize your working directory.

Note

This tutorial assumes that you are using a tutorial-specific HCP Terraform organization with a global variable set of your AWS credentials. Review the Create a Credential Variable Set for detailed guidance. If you are using a scoped variable set, assign it to your new workspace now.

Now apply the configuration. Respond to the confirmation prompt with a yes to create the example infrastructure.

$ terraform apply

## ...

Apply complete! Resources: 40 added, 0 changed, 0 destroyed.

Outputs:

public_dns_name = "lb-GHB-my-project-dev-816845261.us-east-2.elb.amazonaws.com"

Tip

This tutorial shows the output for Terraform commands run with the Terraform CLI. If you are following the HCP Terraform workflow, the output may differ slightly but the results will be the same.

If you use HCP Terraform to provision your resources, your workspace now displays the list of all of the resources it manages.