Terraform vs. Terragrunt: Choosing the Right Tool for Infrastructure as Code

Understanding the Differences and How to Use Them Together for Complex Deployments

terragrunt vs terraform

Infrastructure as code (IaC) has revolutionized the way modern software development teams operate. Tools like Terraform and Terragrunt have made it possible to manage complex infrastructure resources in a programmatic and repeatable way. While both tools serve similar purposes, they have distinct differences that are worth exploring.

Terraform is an open-source tool that provides a declarative language for defining and provisioning infrastructure resources. It allows teams to define infrastructure resources as code, making it easier to version control, test, and deploy changes. With Terraform, developers can define infrastructure resources in a high-level language and then use it to provision and manage resources across multiple providers, including AWS, Azure, and GCP.

Terragrunt, on the other hand, is a wrapper tool for Terraform that provides additional functionality for managing infrastructure. It provides a way to organize and modularize Terraform code, making it easier to reuse and maintain. Terragrunt uses a hierarchical file structure to manage the Terraform codebase, with each module having its own configuration and state files. This approach makes it easier to manage complex infrastructure deployments, especially those involving multiple environments, such as development, staging, and production.

To better understand the differences between Terraform and Terragrunt, let’s look at an example.

Suppose we are tasked with deploying a web application that consists of a frontend server running on EC2 instances, a backend server running on RDS instances, an S3 bucket for storing static assets, and a CloudFront distribution for serving the static assets. Furthermore, we need to deploy this application to two different environments — staging and production — each with its own set of resources.

Using Terraform, we would define the resources needed for the application in separate configuration files for each environment. For example, here’s a snippet of code that defines an EC2 instance for the frontend server in the staging environment:

resource "aws_instance" "frontend" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  tags = {
    Environment = "staging"
    Name        = "frontend"
  }
}

We would repeat this process for each resource needed in the staging environment and then use the terraform apply command to provision the resources on AWS. We would then repeat this process for the production environment.

Using Terragrunt, we would organize the Terraform code into modules that can be reused across both environments. For example, we might have a module that defines the backend server and another module that defines the frontend server. Here’s a snippet of code that defines the frontend module:

terraform {
  source = "../modules/frontend"
}

inputs = {
  environment = "staging"
  instance_type = "t2.micro"
}

We would then use Terragrunt to provision the resources for both the staging and production environments by passing in different input variables for each environment. For example, we might run the terragrunt apply-all command to provision the resources for both environments.

Terragrunt provides additional functionality that makes it easier to manage the infrastructure resources across multiple environments. For example, we can use Terragrunt to manage the state files for the Terraform deployments, ensuring that the state is consistent across all environments. We can also use Terragrunt to manage the dependencies between modules, ensuring that the resources are provisioned in the correct order.

In conclusion, while Terraform and Terragrunt have distinct differences, they can be used together to manage complex infrastructure deployments. Terraform provides a high-level language for defining resources, while Terragrunt provides additional functionality for managing the Terraform codebase across multiple environments. By using these tools in combination, we can create a scalable and maintainable infrastructure deployment process.