terraform-module

Terraform Module

Instructions

Step 1: Gather Requirements

Ask:

1. What AWS resources are needed? (VPC, ECS, Lambda, RDS, S3, CloudFront)
2. What environment? (dev, staging, production, or multi-environment)
3. What compliance requirements? (encryption at rest, VPC isolation, logging)
4. Existing infrastructure to integrate with? (VPC ID, subnets, security groups)
5. State backend? (S3+DynamoDB, Terraform Cloud, local)

Step 2: Module Structure

Create the standard module layout:

modules/
  my-service/
    main.tf          # Primary resource definitions
    variables.tf     # Input variable declarations
    outputs.tf       # Output value declarations
    versions.tf      # Provider and terraform version constraints
    locals.tf        # Local values and computed expressions
    data.tf          # Data sources
    README.md        # Module documentation

versions.tf (always include):

terraform {
  required_version = ">= 1.5"

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

Step 3: Variable Definitions

Define variables with descriptions, types, and validation:

variable "environment" {
  description = "Deployment environment (dev, staging, production)"
  type        = string

  validation {
    condition     = contains(["dev", "staging", "production"], var.environment)
    error_message = "Environment must be dev, staging, or production."
  }
}

variable "service_name" {
  description = "Name of the service, used for resource naming and tagging"
  type        = string

  validation {
    condition     = can(regex("^[a-z][a-z0-9-]{2,28}$", var.service_name))
    error_message = "Service name must be lowercase, start with a letter, 3-29 chars."
  }
}

variable "vpc_config" {
  description = "VPC configuration for the service"
  type = object({
    vpc_id             = string
    private_subnet_ids = list(string)
    public_subnet_ids  = list(string)
  })
}

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