Terraform Tutorial — Module Structure

A Terraform module is simply a directory containing .tf files. The standard structure makes modules predictable and easy to understand.

---

Standard Module Layout

modules/vpc/
├── main.tf          ← Resources
├── variables.tf     ← Input variables
├── outputs.tf       ← Output values
├── versions.tf      ← Provider/Terraform version constraints
└── README.md        ← Documentation

---

main.tf — Resources

# modules/vpc/main.tf

resource "aws_vpc" "this" {
  cidr_block           = var.cidr_block
  enable_dns_hostnames = var.enable_dns_hostnames
  enable_dns_support   = true

  tags = merge(var.tags, {
    Name = "${var.name}-vpc"
  })
}

resource "aws_subnet" "public" {
  count                   = length(var.public_subnets)
  vpc_id                  = aws_vpc.this.id
  cidr_block              = var.public_subnets[count.index]
  availability_zone       = var.availability_zones[count.index]
  map_public_ip_on_launch = true

  tags = merge(var.tags, {
    Name = "${var.name}-public-${count.index + 1}"
  })
}

---

variables.tf — Inputs

# modules/vpc/variables.tf

variable "name" {
  type        = string
  description = "Name prefix for all resources"
}

variable "cidr_block" {
  type        = string
  default     = "10.0.0.0/16"
  description = "CIDR block for the VPC"
}

variable "public_subnets" {
  type        = list(string)
  default     = ["10.0.1.0/24", "10.0.2.0/24"]
  description = "List of public subnet CIDR blocks"
}

variable "availability_zones" {
  type        = list(string)
  description = "List of availability zones"
}

variable "enable_dns_hostnames" {
  type    = bool
  default = true
}

variable "tags" {
  type    = map(string)
  default = {}
}

---

outputs.tf — Outputs

# modules/vpc/outputs.tf

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

output "public_subnet_ids" {
  value       = aws_subnet.public[*].id
  description = "List of public subnet IDs"
}

output "vpc_cidr" {
  value       = aws_vpc.this.cidr_block
  description = "CIDR block of the VPC"
}

---

versions.tf — Constraints

# modules/vpc/versions.tf

terraform {
  required_version = ">= 1.5.0"

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

---

What’s Next?

You know the structure. Let’s learn how to call a module from your root configuration.

---

← Why Modules? Calling a Module →