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Terraform Modules - How to Create, Use, and Publish (2025 Guide)

Complete guide to Terraform modules: creating, using, versioning, and publishing reusable infrastructure code. Step-by-step guide with code examples and best...

LLuca Berton1 min read

What Are Terraform Modules?

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A module is a container for multiple resources that are used together. Every Terraform configuration is technically a module (the root module). Child modules let you organize and reuse infrastructure code.

Using a Module

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module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.0"
 
  name = "my-vpc"
  cidr = "10.0.0.0/16"
 
  azs             = ["us-east-1a", "us-east-1b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]
 
  enable_nat_gateway = true
}

Module Sources

# 
# Terraform Registry (recommended)
source = "terraform-aws-modules/vpc/aws"
 
# GitHub
source = "github.com/org/repo//modules/vpc"
 
# Local path
source = "./modules/networking"
 
# S3 bucket
source = "s3::https://bucket.s3.amazonaws.com/modules/vpc.zip"
 
# Git over SSH
source = "git@github.com:org/repo.git//modules/vpc?ref=v1.0.0"

Creating a Module

#

Module Structure

# 
modules/networking/
├── main.tf          # Resources
├── variables.tf     # Input variables
├── outputs.tf       # Output values
├── versions.tf      # Required providers
└── README.md        # Documentation

Example Module

#

variables.tf:

variable "vpc_cidr" {
  type        = string
  description = "CIDR block for the VPC"
}
 
variable "environment" {
  type        = string
  description = "Environment name (dev, staging, prod)"
}

main.tf:

resource "aws_vpc" "this" {
  cidr_block           = var.vpc_cidr
  enable_dns_hostnames = true
  tags = { Name = "${var.environment}-vpc" }
}

outputs.tf:

output "vpc_id" {
  value       = aws_vpc.this.id
  description = "The ID of the VPC"
}

Module Best Practices

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  1. Keep modules focused — one module per logical component
  2. Always version modules — use semantic versioning
  3. Document inputs and outputs — use descriptions on every variable and output
  4. Don't hardcode providers — let the caller configure providers
  5. Use terraform-docs to auto-generate documentation
  6. Test modules with Terratest or terraform test

Learn More

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Related: How to install AWS CLI on macOS using Homebrew — set up AWS CLI in minutes.

#modules#reusability#registry

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