Nimendra's Notes 🪴

07. Modules

3 min read

terraform modules

Terraform Use Output from Another Module: Effective Guide

Core Idea

A Terraform module is a reusable bundle of .tf files in its own directory: every configuration is already a root module, and calling one from another makes it a child module.

  • Root modules versus child modules, and why even a single _locals_ block counts as a root module.
  • Local modules versus published ones (registry or VCS with a tag), called with a module block.
  • Modules versus resources: a resource is one piece of infrastructure, a module is a reusable group of them.

todo

What is Terraform Module

What Are Terraform Modules and How to Use Them - Tutorial

Abstract

A Terraform module is a collection of standard configuration files in a dedicated directory. Terraform modules encapsulate groups of resources dedicated to one task, reducing the amount of code you have to develop for similar infrastructure components.

A typical module can look like this:

.
├── main.tf
├── outputs.tf
├── README.md
└── variables.tf

practically any Terraform configuration is already a module in itself.

If you run Terraform in this directory, those configuration files would be considered a root module. It means that this configuration is the base of your operation, a core that you can expand further.

Difference between resources and modules in Terraform?

A resource in Terraform describes a piece of infrastructure that is going to be created (e.g., a VPC, a subnet, an ec2 instance, etc), whereas a module is a collection of resources that are used together to achieve a reusable use case.

Types of Modules

Root Module

The root module consists of all the resources defined in the .tf files in a Terraform configuration, meaning that all Terraform configurations have their own root module. 

Even if you are simply creating a main.tf that has just a locals block inside of it with a local variable, that is still considered a root module. 

This can be confusing, but keep in mind that every Terraform configuration can become a reusable module for other configurations. Every module can call other modules, and all of the modules called inside another module are considered child modules.

Child Module

Calling a child module means to include all the resources defined in that module in the current configuration. This is done by using a module block inside your Terraform configuration:

module "webservers" {
   source = "../webservers"
}

You can call the same module as many times as you want and configure it to your liking.

Local module

A local module is a module that wasn’t published in any registry and when it is sourced, it is using the path to that particular module.

Published module

A published module refers to a module that has been pushed to a Terraform Registry, or even simply on a VCS and has a tag associated with it. When a published module is sourced, the URL of that module is used either from the registry or from the VCS itself.

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