Terragrunt for DRY Coding and Streamlined Configuration

Overview

In the rapidly evolving landscape of Infrastructure as Code (IaC), Terraform has asserted itself as a powerhouse for provisioning and managing infrastructure across diverse cloud providers. However, as infrastructures become complex, managing Terraform configurations can become daunting. Enter Terragrunt, a formidable companion to Terraform designed to enhance workflow scalability and maintainability. In this comprehensive guide, we will take a deep dive into Terragrunt, unraveling its uses, providing real-world examples, and exploring essential commands that empower infrastructure engineers to navigate the complexities of modern cloud architecture.

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Terragrunt

Terragrunt can be perceived as a strategic layer atop Terraform, serving as a thin wrapper that introduces additional tools to streamline workflows. Its primary objectives include promoting the principles of “Don’t Repeat Yourself” (DRY) coding, efficient remote state management, and improved configurability through environment variables.

Let’s explore the key features that make Terragrunt an indispensable tool for infrastructure management:

DRY Configurations

Terragrunt excels at keeping Terraform configurations DRY. By allowing the creation of reusable modules, it mitigates redundancy and significantly enhances the maintainability of infrastructure code. This means common configurations, such as those related to networking or security, can be encapsulated in modules and effortlessly reused across different environments.

Remote State Management

Effectively managing Terraform state across diverse environments and collaborative teams can be a logistical nightmare. Terragrunt simplifies this challenge by automating the configuration of remote state backends, such as Amazon S3 or Azure Storage. This ensures consistency and facilitates seamless collaboration among team members, even in distributed and dynamic settings.

Environment Variables

Flexibility is a hallmark of Terragrunt, and its support for environment variables exemplifies this trait. Infrastructure engineers can effortlessly manage configurations for multiple environments—dev, staging, production—without duplicating code. This capability proves invaluable when dealing with varying settings across different deployment stages.

Dependency Management

Terragrunt introduces a sophisticated approach to handling dependencies between Terraform modules. This becomes particularly relevant when dealing with modularized infrastructures with intricate interdependencies. Terragrunt’s ability to orchestrate the application of modules in the correct order ensures a coherent and predictable deployment process.

Example Usage

Let’s walk through a detailed example to illustrate the power of Terragrunt in a real-world scenario. In this example, we’ll create a simple infrastructure with AWS using Terraform, and Terragrunt will be employed to enhance the organization, maintainability, and scalability of the project.

Folder Structure

Organize the project with separate folders for each component:

├── terragrunt.hcl
├── modules
│   ├── vpc
│   │   ├── main.tf
│   │   └── variables.tf
│   ├── subnets
│   │   ├── main.tf
│   │   └── variables.tf
└── environments
    ├── dev
    │   ├── terragrunt.hcl
    │   └── terraform.tfvars
    ├── staging
    │   ├── terragrunt.hcl
    │   └── terraform.tfvars
    └── prod
        ├── terragrunt.hcl
        └── terraform.tfvars

├── terragrunt.hcl

├── modules

│ ├── vpc

│ │ ├── main.tf

│ │ └── variables.tf

│ ├── subnets

│ │ ├── main.tf

│ │ └── variables.tf

└── environments

├── dev

│ ├── terragrunt.hcl

│ └── terraform.tfvars

├── staging

│ ├── terragrunt.hcl

│ └── terraform.tfvars

└── prod

├── terragrunt.hcl

└── terraform.tfvars

Terragrunt Configuration

In the root directory, create a terragrunt.hcl file to define the remote state configuration:

remote_state {
backend = "s3"
config = {
   bucket         = "my-terraform-state-bucket"
   key            = "${path_relative_to_include()}/terraform.tfstate"
   region         = "us-east-1"
}
}

remote_state {

backend = "s3"

config = {

bucket = "my-terraform-state-bucket"

key = "${path_relative_to_include()}/terraform.tfstate"

region = "us-east-1"

}

Module Configurations

Inside the modules directory, create modules for VPC, subnets, and Amazon EC2. Each module should have its main.tf and variables.tf files:

modules/vpc/main.tf

resource "aws_vpc" "main" {
  cidr_block = var.vpc_cidr
  enable_dns_support = true
  enable_dns_hostnames = true
  tags = {
    Name = "my-vpc"
  }
}

resource "aws_vpc" "main" {

cidr_block = var.vpc_cidr

enable_dns_support = true

enable_dns_hostnames = true

tags = {

Name = "my-vpc"

}

modules/vpc/variables.tf

variable "vpc_cidr" {
  description = "CIDR block for the VPC"
  type        = string
}

variable "vpc_cidr" {

description = "CIDR block for the VPC"

type = string

}

modules/subnets/main.tf

resource "aws_subnet" "main" {
  count = length(var.subnet_cidrs)

  cidr_block = var.subnet_cidrs[count.index]
  vpc_id     = var.vpc_id

  tags = {
    Name = "subnet-${count.index + 1}"
  }
}
modules/subnets/variables.tf
variable "subnet_cidrs" {
  description = "List of CIDR blocks for subnets"
  type        = list(string)
}
variable "vpc_id" {
  description = "ID of the VPC"
  type        = string
}

resource "aws_subnet" "main" {

count = length(var.subnet_cidrs)

cidr_block = var.subnet_cidrs[count.index]

vpc_id = var.vpc_id

tags = {

Name = "subnet-${count.index + 1}"

}

modules/subnets/variables.tf

variable "subnet_cidrs" {

description = "List of CIDR blocks for subnets"

type = list(string)

}

variable "vpc_id" {

description = "ID of the VPC"

type = string

}

Environment Configurations

Create separate directories for each environment (dev, staging, prod) inside the environment’s directory. Each environment should have its terragrunt.hcl and terraform.tfvars files.

environments/dev/terragrunt.hcl

remote_state {
  backend = "s3"
  config = {
    bucket         = "my-terraform-state-bucket"
    key            = "${path_relative_to_include()}/terraform.tfstate"
    region         = "us-east-1"
  }
}
include {
  path = "${find_in_parent_folders()}/modules"
}
inputs = {
  vpc_cidr     = "10.0.0.0/16"
  subnet_cidrs = ["10.0.1.0/24", "10.0.2.0/24"]
  ami          = "ami-12345678"
  instance_type = "t2.micro"
}

remote_state {

backend = "s3"

config = {

bucket = "my-terraform-state-bucket"

key = "${path_relative_to_include()}/terraform.tfstate"

region = "us-east-1"

}

include {

path = "${find_in_parent_folders()}/modules"

}

inputs = {

vpc_cidr = "10.0.0.0/16"

subnet_cidrs = ["10.0.1.0/24", "10.0.2.0/24"]

ami = "ami-12345678"

instance_type = "t2.micro"

}

environments/dev/terraform.tfvars

vpc_id     = "your-vpc-id-from-previous-run"
subnet_ids = "your-subnet-ids-from-previous-run"

1 2	vpc_id = "your-vpc-id-from-previous-run" subnet_ids = "your-subnet-ids-from-previous-run"

Terragrunt Commands

Terragrunt commands closely mirror Terraform commands, offering a seamless transition for users. Essential commands include:

terragrunt init: Initializes the working directory.
terragrunt plan: Provides an execution plan.
terragrunt apply: Applies changes to the infrastructure.
terragrunt destroy: Safely dismantles the infrastructure.

Terragrunt emerges as a force multiplier for Terraform, augmenting its capabilities and transforming it into a more adaptable and scalable tool for real-world infrastructure management. By addressing critical issues such as code repetition, state management, and environment-specific configurations, Terragrunt stands as a robust solution for navigating the intricacies of modern cloud architecture.

As you embark on your Infrastructure as Code journey, consider integrating Terragrunt into your toolkit. Its flexibility, modularity, and ease of use can significantly contribute to the success of your infrastructure projects. In the dynamic landscape of cloud computing, Terragrunt is not just a tool—it’s a strategic ally empowering infrastructure engineers to conquer the challenges of tomorrow’s digital infrastructure.

Drop a query if you have any questions regarding Terragrunt and we will get back to you quickly.

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FAQs

1. What is Terragrunt, and how does it differ from Terraform?

ANS: – Terragrunt is a thin wrapper for Terraform, enhancing its functionality. While Terraform is focused on provisioning infrastructure, Terragrunt facilitates code reuse, remote state management, and environment-specific configurations, streamlining complex workflows.

2. How does Terragrunt handle remote state management?

ANS: – Terragrunt simplifies remote state management by automating the configuration of backends, such as Amazon S3 or Azure Storage. This ensures consistency in state storage across environments and facilitates collaboration among team members by centralizing the storage and locking of Terraform state files.

WRITTEN BY Dharshan Kumar K S

Dharshan Kumar is a Research Associate at CloudThat. He has a working knowledge of various cloud platforms such as AWS, Microsoft, ad GCP. He is interested to learn more about AWS's Well-Architected Framework and writes about them.