Creating Your Own Module From Scratch

Building a well-structured, versioned Terraform module ensures consistency, reusability, and easy collaboration across teams. In this guide, we’ll walk through:

Directory layout
Input declarations and validations
Resource definitions
Output exports
Example usage
Versioning best practices
Documentation tips

1. Module Directory Structure

Begin by creating a top-level folder for your module. Inside, organize files as follows:

Path	Purpose
my-module/	Root directory for your module
├─ main.tf	Core resource definitions
├─ variables.tf	Input variable declarations & validations
├─ outputs.tf	Exported values for external configurations
└─ examples/simple/main.tf	Minimal example demonstrating module usage

my-module/
├── main.tf
├── variables.tf
├── outputs.tf
└── examples/
    └── simple/
        └── main.tf

2. Declare and Parameterize Inputs

In variables.tf, declare all module inputs, set types, defaults, and add validation:

variable "instance_count" {
  description = "Number of EC2 instances to create"
  type        = number
  default     = 1

  validation {
    condition     = var.instance_count > 0
    error_message = "instance_count must be at least 1"
  }
}

variable "ami_id" {
  description = "AMI ID for the EC2 instances"
  type        = string
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t3.micro"
}

variable "aws_region" {
  description = "AWS region to deploy resources"
  type        = string
  default     = "us-west-2"
}

Use validation blocks to enforce constraints early and prevent invalid configurations.

3. Define Resources Using Inputs

Start by pinning provider versions:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = var.aws_region
}

Then, reference your variables in main.tf:

resource "aws_instance" "example" {
  count         = var.instance_count
  ami           = var.ami_id
  instance_type = var.instance_type

  tags = {
    Name = "example-instance-${count.index + 1}"
  }
}

Avoid hard-coding AMI IDs across regions. Consider using data "aws_ami" to dynamically look up the latest image.

4. Expose Outputs

In outputs.tf, export the values that other modules or root configurations will consume:

output "instance_ids" {
  description = "IDs of the created EC2 instances"
  value       = aws_instance.example[*].id
}

output "public_ips" {
  description = "Public IP addresses of the created EC2 instances"
  value       = aws_instance.example[*].public_ip
}

If outputs contain sensitive data (e.g., private keys), set sensitive = true to prevent accidental exposure.

5. Provide Usage Examples

Under examples/simple/main.tf, demonstrate a minimal working invocation:

module "ec2_example" {
  source         = "../../"
  instance_count = 2
  ami_id         = "ami-0c55b159cbfafe1f0"
  instance_type  = "t3.micro"
  aws_region     = "us-west-2"
}

output "created_ids" {
  value = module.ec2_example.instance_ids
}

Run the following commands:

Command	Description
terraform init	Initialize plugins and backend
terraform plan	Preview planned changes
terraform apply	Apply the configuration
terraform destroy	Tear down the created resources

cd examples/simple
terraform init
terraform apply

6. Versioning and Collaboration

Follow these guidelines to keep your module maintainable:

Use Semantic Versioning (e.g., v1.0.0, v1.1.0)
Tag releases in Git (git tag v1.0.0)
Maintain a CHANGELOG.md to record feature additions and fixes

7. Documentation and Comments

Consistently document your module to help users onboard quickly:

Add a header comment in each .tf file summarizing its purpose
Comment complex logic (e.g., loops, conditionals) in main.tf
Describe variable constraints and recommended values next to their declarations

Links and References

Watch Video

Custom Modules vs Community Modules

Demo Creating Your Own Module From Scratch

Introduction

Terragrunt - Good to Know Concepts & Ideas

Terragrunt Configuration

Terragrunt Commands

Terragrunt Functions

Terragrunt Blocks

Terragrunt Attributes

Managing Remote State with Terragrunt

Terragrunt Modules

Building our first AWS Demo with Terragrunt

Conclusion

Terragrunt - Basic Concepts

Creating Your Own Module From Scratch

1. Module Directory Structure

2. Declare and Parameterize Inputs

3. Define Resources Using Inputs

4. Expose Outputs

5. Provide Usage Examples

6. Versioning and Collaboration

7. Documentation and Comments

Links and References

Watch Video

​1. Module Directory Structure

​2. Declare and Parameterize Inputs

​3. Define Resources Using Inputs

​4. Expose Outputs

​5. Provide Usage Examples

​6. Versioning and Collaboration

​7. Documentation and Comments

​Links and References

Watch Video

1. Module Directory Structure

2. Declare and Parameterize Inputs

3. Define Resources Using Inputs

4. Expose Outputs

5. Provide Usage Examples

6. Versioning and Collaboration

7. Documentation and Comments

Links and References