Terragrunt for DRY configurations in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does DRY stand for in Terragrunt configurations?

DRY stands for "Don't Repeat Yourself." It means writing code or configurations once and reusing them to avoid duplication.

beginner

How does Terragrunt help with DRY in Terraform projects?

Terragrunt lets you keep common Terraform code in one place and reuse it across many modules, so you don't copy-paste the same code multiple times.

beginner

What is a common file used by Terragrunt to define reusable configurations?

Terragrunt uses a file called terragrunt.hcl to store reusable settings like backend configs and variables.

intermediate

What is the purpose of the include block in a Terragrunt configuration?

The include block lets a Terragrunt config reuse settings from a parent or common config file, helping keep things DRY.

intermediate

Why is using Terragrunt beneficial for managing multiple Terraform environments?

Terragrunt helps manage multiple environments by sharing common configs and only changing what’s different, making updates easier and less error-prone.

What is the main goal of using Terragrunt with Terraform?

A To avoid repeating configuration code

B To replace Terraform completely

C To write Terraform code in a new language

D To deploy applications faster

Terragrunt is designed to help avoid repeating Terraform configuration code by enabling reuse and better organization.

Which file does Terragrunt use to store reusable configuration blocks?

A terraform.tfstate

B main.tf

C terragrunt.hcl

D variables.tf

Terragrunt uses the terragrunt.hcl file to define reusable configuration blocks.

What does the include block in Terragrunt do?

A Creates new Terraform modules

B Runs Terraform commands automatically

C Defines variables for Terraform

D Imports settings from another Terragrunt config

The include block imports settings from another Terragrunt configuration file to reuse common settings.

How does Terragrunt help when managing multiple environments like dev and prod?

A By merging all environments into one

B By sharing common configs and only changing environment-specific parts

C By deleting unused environments automatically

D By converting Terraform code to scripts

Terragrunt helps manage multiple environments by sharing common configurations and customizing only what differs.

Which of these is NOT a benefit of using Terragrunt?

A Replacing Terraform's core engine

B Simplifying Terraform configuration management

C Avoiding code duplication

D Easier environment management

Terragrunt does not replace Terraform's core engine; it works alongside Terraform to improve configuration management.

Explain how Terragrunt helps keep Terraform configurations DRY and why this is useful.

Think about how copying code can cause mistakes and how sharing code helps.

Describe the role of the include block in Terragrunt and how it supports configuration reuse.

It's like inheriting settings from a shared file.

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