Terraform Modules Overview

Terraform Modules Overview

Managing infrastructure-as-code with Terraform is great — until suddenly, it’s not. What starts as a simple set of configuration files can quickly turn into an intricate web of resources, variables, outputs, and providers.

To simplify your operations, break up your configuration into reusable, composable pieces called modules. With them, your Terraform code evolves in an understandable, organized way, even as complexity increases.

This article covers the module basics you need to level up your Terraform skills. You’ll also learn module best practices to apply them right away.

Is Terraform a Configuration Management Tool?

Terraform is sometimes confused with configuration management tools like Ansible, Puppet, or Chef. But Terraform actually solves a different problem — infrastructure provisioning and management.

Configuration management tools focus on controlling resource settings once infrastructure already exists. For example, Puppet is helpful for ensuring that packages, files, and services are set up correctly on hundreds of virtual machines (VM). It covers the “day 2” management of existing resources.

Terraform instead tackles the “day 1” challenge of actually creating reusable infrastructure in the first place — whether on-premises or in a cloud. It provides a consistent way to declare and deploy the networks, instances, and services needed for an application to AWS, Azure, etc.

We often see IT leaders bring in IT advisory services to help their teams ramp up best practices on Terraform. The consultants recommend complementing Terraform’s provisioning strengths with ongoing configuration management for comprehensive lifecycle automation.

So, why does Terraform get labeled as a configuration management competitor? Part of it is the “infrastructure as code” overlap. Like Puppet, Terraform enables infrastructure to be codified and shared instead of relying on fragile manual processes. Teams can check in the configs to version control and collaborate on infrastructure changes, just like application code.

But Terraform takes a different approach, suited to provisioning rather than configuring. Instead of pushing settings to resources imperatively, Terraform generates ideal infrastructure plans from declarative descriptions and then reconciles any drifts toward the desired end-goal state. 

For example, a Terraform config would define “I need a VM instance with these disks, interfaces, and tags.” It doesn’t focus on how to get there — Terraform handles installing and configuring everything behind the scenes. This makes infrastructure more portable and repeatable compared to instance-by-instance scripts and commands.

Now, tools like Terraform and Puppet complement each other nicely once understood. Terraform initially sets up the scaffolding — it “builds the house.” Puppet then customizes and operates the environment — it “arranges and manages the furniture.” One focuses on provisioning infrastructure, the other on ongoing configuration.

So, what does Terraform mean? Let’s give it a clear definition.

The Definition of Terraform

Terraform is a software tool created by HashiCorp that lets you describe the resources your applications need and then build and manage them automatically. Instead of clicking around cloud consoles or running CLI commands, you can define infrastructure in simple configuration files that others can read and edit. It works across all the major cloud platforms, like AWS, Azure, and Google Cloud. No wonder nearly 35,208 companies currently use Terraform. 

The key benefit is avoiding the headache of manually configuring your infrastructure components. Do you want developers to spend days scripting up VMs and networks by hand, server after server? That’s what Terraform handles for you — just describe the desired infrastructure and let Terraform do the provisioning automatically.

In this way, Terraform allows you to create increasingly complex configurations as you manage your infrastructure with it. Terraform configuration files and directories don’t have an intrinsic complexity limit, so you can continue to write and update your configuration files in the same directory. Nevertheless, if you continue, you may run into the following problems:

• You’ll have a much harder time understanding the configuration files.
• Configuration updates will become more complicated since one section’s update can have unintended consequences for other sections.
• As you configure separate development, staging, and production environments, you will have more duplication of configuration blocks, which will cause an increasing amount of burden when updating your configuration.
• Sharing configurations between projects and teams is extremely error-prone and difficult to maintain if you cut and paste blocks between projects.

This is where Terraform modules can assist by encapsulating reusable, composable blocks of infrastructure that can be shared, versioned, and maintained efficiently across projects. To understand exactly how they can assist you, let’s first define Terraform modules.

What Are the Terraform Modules?