Terragrunt for DRY configurations in Terraform - Mini Project: Build & Apply

Terragrunt for DRY configurations

📖 Scenario: You are managing infrastructure for a company that has multiple environments: development, staging, and production. Each environment uses similar Terraform modules but with different settings. To avoid repeating the same configuration in each environment, you want to use Terragrunt to keep your Terraform code DRY (Don't Repeat Yourself).

🎯 Goal: Build a Terragrunt configuration that uses a common Terraform module with shared settings, and environment-specific overrides, to manage infrastructure for three environments without repeating code.

📋 What You'll Learn

Create a Terragrunt root configuration with common settings

Create environment-specific Terragrunt configurations that inherit from the root

Use the terraform block to specify the source module

Use the inputs block to pass variables to the Terraform module

Demonstrate how to keep configurations DRY using Terragrunt's include feature

💡 Why This Matters

🌍 Real World

Companies often manage multiple environments with similar infrastructure. Terragrunt helps avoid repeating code by sharing common configuration and allowing environment-specific overrides.

💼 Career

Understanding Terragrunt is valuable for cloud engineers and DevOps professionals who manage infrastructure as code efficiently and maintainably.

1

Create the root Terragrunt configuration

Create a file named terragrunt.hcl in the root folder with a terraform block that sets the source to git::https://github.com/example/infrastructure-modules.git//network. Also, add an inputs block with region = "us-east-1" and environment = "root".

Terraform

# Your code here

Hint

Use the terraform block to specify the module source URL. Then add an inputs block with the required variables.

2

Create the development environment Terragrunt configuration

Create a file named dev/terragrunt.hcl that uses the include block to inherit from the root terragrunt.hcl. Override the inputs block to set environment = "dev" and add instance_count = 1.

Terraform

terraform {
  source = "git::https://github.com/example/infrastructure-modules.git//network"
}

inputs = {
  region      = "us-east-1"
  environment = "root"
}

# Your code here

Hint

Use the include block with find_in_parent_folders() to inherit root settings. Then override inputs with environment-specific values.

3

Create the staging environment Terragrunt configuration

Create a file named staging/terragrunt.hcl that includes the root configuration using include. Override the inputs block to set environment = "staging" and instance_count = 2.

Terraform

terraform {
  source = "git::https://github.com/example/infrastructure-modules.git//network"
}

inputs = {
  region      = "us-east-1"
  environment = "root"
}

include {
  path = find_in_parent_folders()
}

inputs = {
  environment    = "dev"
  instance_count = 1
}

# Your code here

Hint

Similar to the dev environment, use include and override inputs for staging.

4

Create the production environment Terragrunt configuration

Create a file named prod/terragrunt.hcl that includes the root configuration using include. Override the inputs block to set environment = "prod" and instance_count = 3. This completes the DRY Terragrunt setup for all environments.

Terraform

terraform {
  source = "git::https://github.com/example/infrastructure-modules.git//network"
}

inputs = {
  region      = "us-east-1"
  environment = "root"
}

include {
  path = find_in_parent_folders()
}

inputs = {
  environment    = "dev"
  instance_count = 1
}

// staging/terragrunt.hcl
include {
  path = find_in_parent_folders()
}

inputs = {
  environment    = "staging"
  instance_count = 2
}

# Your code here

Hint

Follow the same pattern as previous environments to complete the production configuration.

Practice

1. What is the main purpose of using Terragrunt with Terraform?

easy

A. To reuse Terraform configurations and avoid repeating code

B. To replace Terraform with a new tool

C. To write Terraform code in a different programming language

D. To deploy applications without infrastructure

Solution

1. Step 1: Understand Terragrunt's role

   Terragrunt is designed to help reuse and share Terraform code, making it easier to manage infrastructure without repeating code.

2. Step 2: Compare options

   Options B, C, and D describe incorrect uses or misunderstandings of Terragrunt's purpose.

3. Final Answer:

   To reuse Terraform configurations and avoid repeating code -> Option A

4. Quick Check:

   Terragrunt = DRY Terraform code reuse [OK]

Hint: Terragrunt helps avoid repeating Terraform code [OK]

Common Mistakes:

• Thinking Terragrunt replaces Terraform
• Believing Terragrunt changes Terraform language
• Confusing Terragrunt with application deployment tools

2. Which of the following is the correct way to include a Terraform module using Terragrunt?

easy

A. module "app" { source = "./app" }

B. include { path = find_in_parent_folders() }

C. terraform { backend = "s3" }

D. resource "aws_instance" "web" {}

Solution

1. Step 1: Identify Terragrunt syntax for including configs

   Terragrunt uses the include block with path = find_in_parent_folders() to reuse parent configs.

2. Step 2: Differentiate from Terraform syntax

   Options A, C, and D are Terraform syntax: A is a module block, C is backend config, D is a resource block, not Terragrunt includes.

3. Final Answer:

   include { path = find_in_parent_folders() } -> Option B

4. Quick Check:

   Terragrunt include uses find_in_parent_folders() [OK]

Hint: Terragrunt includes parent config with include + find_in_parent_folders() [OK]

Common Mistakes:

• Using Terraform module syntax instead of Terragrunt include
• Confusing backend config with include
• Writing resource blocks inside Terragrunt files

3. Given this Terragrunt configuration snippet:

include {
  path = find_in_parent_folders()
}

inputs = {
  region = "us-east-1"
  env    = "prod"
}

What will happen when you run terragrunt apply in this folder?

medium

A. Terragrunt will apply Terraform code without any variables

B. Terragrunt will fail because inputs cannot be used with include

C. Terragrunt will ignore the inputs block and only use parent config

D. Terragrunt will apply Terraform code using the parent config and inputs region=us-east-1, env=prod

Solution

1. Step 1: Understand include and inputs usage

   The include block imports parent config. The inputs block adds or overrides variables for this folder.

2. Step 2: Predict Terragrunt behavior on apply

   Terragrunt merges parent config with local inputs, so region and env variables are set as given.

3. Final Answer:

   Terragrunt will apply Terraform code using the parent config and inputs region=us-east-1, env=prod -> Option D

4. Quick Check:

   Include + inputs = merged config applied [OK]

Hint: Inputs override or add variables when using include [OK]

Common Mistakes:

• Thinking inputs are ignored with include
• Assuming inputs cause errors
• Believing variables are not passed to Terraform

4. You wrote this Terragrunt config:

include {
  path = find_in_parent_folders()
}

inputs = {
  region = "us-west-2"
  env = "dev"
}

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

When running terragrunt apply, you get an error: "Error: Unsupported block type". What is the likely cause?

medium

A. The terraform block cannot be nested inside the inputs block

B. The inputs block must come before include

C. The source path is incorrect

D. The region variable is invalid

Solution

1. Step 1: Check Terragrunt config block usage

   Terragrunt requires the terraform { source = ... } block at the root level. It cannot be nested inside other blocks like inputs.

2. Step 2: Identify error cause

   The error "Unsupported block type" usually means the block is misplaced or invalid in Terragrunt config.

3. Final Answer:

   The terraform block cannot be nested inside the inputs block -> Option A

4. Quick Check:

   Misplaced terraform block causes error [OK]

Hint: Terraform block must be correctly placed in Terragrunt config [OK]

Common Mistakes:

• Placing terraform block inside inputs or include
• Wrong order of blocks causing syntax errors
• Incorrect source path causing unrelated errors

5. You manage multiple environments (dev, staging, prod) with Terragrunt. You want to avoid repeating the backend configuration for each environment. Which approach best follows DRY principles?

hard

A. Define backend only in Terraform modules, not in Terragrunt

B. Copy the backend block into each environment's Terragrunt config

C. Create a root Terragrunt config with backend settings and use include in each environment folder

D. Use different backend types for each environment

Solution

1. Step 1: Understand DRY with Terragrunt

   Terragrunt allows sharing common config via a root config and include blocks in child folders.

2. Step 2: Evaluate options for backend reuse

   Create a root Terragrunt config with backend settings and use include in each environment folder uses root config for backend, avoiding repetition. Copy the backend block into each environment's Terragrunt config repeats code, violating DRY. Define backend only in Terraform modules, not in Terragrunt is incorrect because backend is configured in Terragrunt for remote state. Use different backend types for each environment adds complexity without reuse.

3. Final Answer:

   Create a root Terragrunt config with backend settings and use include in each environment folder -> Option C

4. Quick Check:

   Root config + include = DRY backend config [OK]

Hint: Put shared backend in root config, include it in environments [OK]

Common Mistakes:

• Copying backend config to each environment
• Configuring backend only in Terraform modules
• Using different backends unnecessarily