Understanding Terragrunt Stacks in Simple Terms

What is Terragrunt?

Terragrunt is a tool that helps you manage Terraform code in an easier and more organized way. It removes the need to write the same Terraform code multiple times by using configurations that can be reused.

What is a Terragrunt Stack?

A Terragrunt Stack is a collection of different Terraform modules that work together to create a complete infrastructure setup. Instead of running each module separately, a stack allows you to apply all of them in a structured way, ensuring everything is deployed in the right order.

Why Do We Need a Terragrunt Stack?

Managing infrastructure can be complex, especially when multiple components (like networks, storage, and compute resources) depend on each other. A Terragrunt Stack helps by:

✅ Running all Terraform modules at once instead of one by one.
✅ Automatically applying modules in the right order based on dependencies.
✅ Allowing easy sharing of values (like security group IDs) between different modules.
✅ Avoiding duplicate code and making infrastructure management simple.

Example of a Terragrunt Stack

Imagine you want to set up the following:

• A VPC (Network)

• An S3 Bucket for Storage

• An EC2 Instance (Virtual Machine)

• A Load Balancer

Instead of running Terraform manually for each one, we can define them as a Terragrunt Stack.

Folder Structure:

my-infra
├── vpc
│   ├── main.tf
│   └── terragrunt.hcl
├── s3
│   ├── main.tf
│   └── terragrunt.hcl
├── ec2
│   ├── main.tf
│   └── terragrunt.hcl
├── load-balancer
│   ├── main.tf
│   └── terragrunt.hcl

Each folder has a terragrunt.hcl file that tells Terragrunt how to apply that module.

How to Use a Terragrunt Stack

1. Running Everything at Once

Instead of applying each Terraform module manually, just run:

cd my-infra
terragrunt run-all apply

This command applies all the modules in the correct order.

2. Destroying Everything

To remove the entire infrastructure:

terragrunt run-all destroy

How Does Terragrunt Handle Dependencies?

Terragrunt ensures that modules run in the right order. For example, if the EC2 instance needs an S3 bucket, we can define this in the ec2/terragrunt.hcl file:

dependency "s3" {
  config_path = "../s3"
}

inputs = {
  s3_bucket_name = dependency.s3.outputs.bucket_name
}

This means the EC2 instance will wait for the S3 bucket to be created first before running.

Why Use a Terragrunt Stack?

✅ Saves Time – No need to run Terraform multiple times.
✅ Reduces Errors – Automatically applies dependencies in the right order.
✅ Makes Infrastructure Reusable – You don’t have to copy-paste Terraform code.
✅ Keeps Things Organized – Helps manage large cloud setups easily.

Final Thoughts

Terragrunt Stacks make managing Terraform projects easier, especially when dealing with complex cloud infrastructure. By using Terragrunt Stacks, you can automate deployments, handle dependencies, and ensure your infrastructure runs smoothly. 🚀

Would you like to see more real-world examples? Let me know in the comments! 😊