Terraform Modules: Reusability and Scalability

Are you tired of writing the same Terraform code over and over again? Do you want to make your infrastructure code more modular and reusable? Look no further than Terraform modules!

Terraform modules are a way to encapsulate and reuse Terraform code. They allow you to define a set of resources that can be used in multiple Terraform configurations. Modules can be shared across teams, projects, and even organizations, making it easier to collaborate and maintain infrastructure code.

In this article, we'll explore the benefits of using Terraform modules, how to create and use them, and best practices for module design.

Benefits of Terraform Modules


One of the main benefits of Terraform modules is reusability. By creating modules for common infrastructure patterns, you can avoid duplicating code across multiple Terraform configurations. This not only saves time but also reduces the risk of errors and inconsistencies.

For example, let's say you need to create a VPC with subnets, security groups, and routing tables. Instead of writing this code from scratch every time, you can create a module that defines these resources. Then, you can reuse this module in multiple Terraform configurations, simply by calling it with different variables.


Another benefit of Terraform modules is scalability. As your infrastructure grows, it can become difficult to manage all the resources in a single Terraform configuration. Modules allow you to break down your infrastructure into smaller, more manageable pieces.

For example, you might have a module for your VPC, another module for your database, and a third module for your web servers. Each module can be developed and tested independently, making it easier to scale your infrastructure over time.


Terraform modules also make it easier to collaborate with others. By creating modules that are easy to understand and use, you can share your infrastructure code with other teams and projects. This can help to standardize infrastructure across your organization and reduce the risk of errors and inconsistencies.

Creating Terraform Modules

Now that we've explored the benefits of Terraform modules, let's dive into how to create them.

Module Structure

A Terraform module is simply a directory containing Terraform code. The directory should have a specific structure, which includes:

Here's an example directory structure for a Terraform module:

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

Module Code

The code inside a Terraform module is just like any other Terraform code. The only difference is that it's encapsulated in a module directory.

Here's an example main.tf file for a module that creates an S3 bucket:

resource "aws_s3_bucket" "bucket" {
  bucket = var.bucket_name
  acl    = "private"

variable "bucket_name" {
  type        = string
  description = "The name of the S3 bucket."

output "bucket_id" {
  value = aws_s3_bucket.bucket.id

This code creates an S3 bucket with a given name and sets the ACL to private. It also defines a variable for the bucket name and an output for the bucket ID.

Module Variables

Variables are used to pass data into a Terraform module. They allow you to customize the behavior of the module without modifying its code.

Here's an example variables.tf file for the S3 bucket module:

variable "bucket_name" {
  type        = string
  description = "The name of the S3 bucket."

This code defines a variable called bucket_name of type string. The description is optional but can be helpful for documenting the variable's purpose.

Module Outputs

Outputs are used to expose data from a Terraform module. They allow you to retrieve information from the module for use in other Terraform configurations.

Here's an example outputs.tf file for the S3 bucket module:

output "bucket_id" {
  value = aws_s3_bucket.bucket.id

This code defines an output called bucket_id that exposes the ID of the S3 bucket created by the module.

Using Terraform Modules

Now that we've created a Terraform module, let's see how to use it in a Terraform configuration.

To use a module, you need to reference its directory in your Terraform code. You can do this using the module block, like this:

module "my-module" {
  source = "./my-module"

  bucket_name = "my-bucket"

resource "aws_s3_bucket_object" "object" {
  bucket = module.my-module.bucket_id
  key    = "example.txt"
  source = "example.txt"

This code references the my-module directory using the source parameter. It also passes in a value for the bucket_name variable.

The aws_s3_bucket_object resource then uses the bucket_id output from the module to specify the target bucket.

Best Practices for Terraform Modules

Now that we know how to create and use Terraform modules, let's explore some best practices for module design.

Keep Modules Small and Focused

One of the most important best practices for Terraform modules is to keep them small and focused. Each module should encapsulate a single piece of infrastructure, such as a VPC or a database.

By keeping modules small and focused, you can make them easier to understand and use. You can also avoid creating modules that are too complex or difficult to maintain.

Use Variables and Outputs Effectively

Variables and outputs are the key to making Terraform modules reusable and customizable. When designing a module, think carefully about the variables and outputs that are needed to make the module flexible and adaptable.

Use variables to allow users to customize the behavior of the module. Use outputs to expose data from the module that can be used in other Terraform configurations.

Document Your Modules

Documentation is essential for making Terraform modules easy to understand and use. Make sure to include a README.md file in your module directory that explains what the module does, how to use it, and any other relevant information.

You should also include comments in your Terraform code that explain what each resource does and how it relates to the module as a whole.

Test Your Modules

Testing is an important part of any software development process, and Terraform modules are no exception. Make sure to test your modules thoroughly before sharing them with others.

You can use tools like Terratest or Kitchen-Terraform to automate testing of your modules. These tools allow you to write tests that verify the behavior of your modules and catch errors before they cause problems in production.

Share Your Modules

Finally, don't forget to share your Terraform modules with others! By sharing your modules, you can help others to avoid duplicating work and make it easier for teams to collaborate on infrastructure code.

You can share your modules on the Terraform Registry, GitHub, or any other platform that supports Terraform modules.


Terraform modules are a powerful tool for making infrastructure code more modular and reusable. By encapsulating common infrastructure patterns in modules, you can save time, reduce errors, and make it easier to collaborate with others.

In this article, we've explored the benefits of Terraform modules, how to create and use them, and best practices for module design. By following these best practices, you can create Terraform modules that are easy to understand, use, and maintain.

So what are you waiting for? Start creating your own Terraform modules today and take your infrastructure code to the next level!

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