Create Reusable Terraform Modules

Advanced20 min

Build, structure, and publish reusable Terraform modules with inputs, outputs, and proper documentation.

Prerequisites

-Terraform installed
-Understanding of Terraform resources
-Git repository for module hosting

Steps

Create the module directory structure

Set up the standard file layout for a Terraform module with variables, outputs, and main configuration.

$ mkdir -p modules/vpc && touch modules/vpc/{main.tf,variables.tf,outputs.tf,README.md,versions.tf}

Define input variables

Declare configurable inputs with types, defaults, descriptions, and validation rules.

$ cat <<'EOF' > modules/vpc/variables.tf variable "vpc_cidr" { type = string description = "CIDR block for the VPC" default = "10.0.0.0/16" validation { condition = can(cidrhost(var.vpc_cidr, 0)) error_message = "Must be a valid CIDR block." } } variable "environment" { type = string description = "Environment name (dev, staging, prod)" } variable "public_subnet_count" { type = number description = "Number of public subnets" default = 2 } EOF

Write the main resource definitions

Implement the core resources that the module creates and manages.

$ cat <<'EOF' > modules/vpc/main.tf resource "aws_vpc" "this" { cidr_block = var.vpc_cidr enable_dns_hostnames = true tags = { Name = "${var.environment}-vpc" Environment = var.environment ManagedBy = "terraform" } } EOF

Use the 'this' naming convention for the primary resource in a single-resource module.

Define module outputs

Export values that consumers of the module will need for connecting other resources.

$ cat <<'EOF' > modules/vpc/outputs.tf output "vpc_id" { description = "The ID of the VPC" value = aws_vpc.this.id } output "vpc_cidr" { description = "The CIDR block of the VPC" value = aws_vpc.this.cidr_block } EOF

Call the module from root configuration

Use the module in your root configuration by referencing the local path and passing variables.

$ cat <<'EOF' > main.tf module "vpc" { source = "./modules/vpc" vpc_cidr = "10.0.0.0/16" environment = "prod" public_subnet_count = 3 } output "vpc_id" { value = module.vpc.vpc_id } EOF

Validate and test the module

Initialize, validate, and plan the configuration to ensure the module works correctly.

$ terraform init && terraform validate && terraform plan

Always run validate before plan to catch syntax and type errors early.

Full Script

full-script.sh

#!/bin/bash
set -euo pipefail

# Terraform Module Scaffolding Script
# Creates a well-structured module with all required files

MODULE_NAME="${1:?Usage: $0 <module-name>}"
MODULE_DIR="modules/${MODULE_NAME}"

echo "==> Creating module: ${MODULE_NAME}"
mkdir -p "${MODULE_DIR}"

cat > "${MODULE_DIR}/versions.tf" <<'EOF'
terraform {
  required_version = ">= 1.5.0"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}
EOF

cat > "${MODULE_DIR}/variables.tf" <<'EOF'
variable "environment" {
  type        = string
  description = "Environment name"
}

variable "tags" {
  type        = map(string)
  description = "Additional tags to apply"
  default     = {}
}
EOF

cat > "${MODULE_DIR}/main.tf" <<EOF
# Main resources for ${MODULE_NAME} module
# TODO: Add your resource definitions here
EOF

cat > "${MODULE_DIR}/outputs.tf" <<EOF
# Outputs for ${MODULE_NAME} module
# TODO: Export values for consumers
EOF

cat > "${MODULE_DIR}/README.md" <<EOF
# ${MODULE_NAME} Module

## Usage

\`\`\`hcl
module "${MODULE_NAME}" {
  source      = "./modules/${MODULE_NAME}"
  environment = "dev"
}
\`\`\`

## Inputs

| Name | Description | Type | Default |
|------|-------------|------|---------|
| environment | Environment name | string | - |
| tags | Additional tags | map(string) | {} |

## Outputs

(Add outputs here)
EOF

echo "==> Module scaffolded at ${MODULE_DIR}/"
ls -la "${MODULE_DIR}/"
echo ""
echo "Next steps:"
echo "  1. Edit ${MODULE_DIR}/main.tf to add resources"
echo "  2. Edit ${MODULE_DIR}/variables.tf to add inputs"
echo "  3. Edit ${MODULE_DIR}/outputs.tf to export values"
echo "  4. Run: terraform init && terraform validate"

FAQ

Discussion

Loading comments...

#!/bin/bash set -euo pipefail # Terraform Module Scaffolding Script # Creates a well-structured module with all required files MODULE_NAME="${1:?Usage: $0 <module-name>}" MODULE_DIR="modules/${MODULE_NAME}" echo "==> Creating module: ${MODULE_NAME}" mkdir -p "${MODULE_DIR}" cat > "${MODULE_DIR}/versions.tf" <<'EOF' terraform { required_version = ">= 1.5.0" required_providers { aws = { source = "hashicorp/aws" version = "~> 5.0" } } } EOF cat > "${MODULE_DIR}/variables.tf" <<'EOF' variable "environment" { type = string description = "Environment name" } variable "tags" { type = map(string) description = "Additional tags to apply" default = {} } EOF cat > "${MODULE_DIR}/main.tf" <<EOF # Main resources for ${MODULE_NAME} module # TODO: Add your resource definitions here EOF cat > "${MODULE_DIR}/outputs.tf" <<EOF # Outputs for ${MODULE_NAME} module # TODO: Export values for consumers EOF cat > "${MODULE_DIR}/README.md" <<EOF # ${MODULE_NAME} Module ## Usage \`\`\`hcl module "${MODULE_NAME}" { source = "./modules/${MODULE_NAME}" environment = "dev" } \`\`\` ## Inputs | Name | Description | Type | Default | |------|-------------|------|---------| | environment | Environment name | string | - | | tags | Additional tags | map(string) | {} | ## Outputs (Add outputs here) EOF echo "==> Module scaffolded at ${MODULE_DIR}/" ls -la "${MODULE_DIR}/" echo "" echo "Next steps:" echo " 1. Edit ${MODULE_DIR}/main.tf to add resources" echo " 2. Edit ${MODULE_DIR}/variables.tf to add inputs" echo " 3. Edit ${MODULE_DIR}/outputs.tf to export values" echo " 4. Run: terraform init && terraform validate"