terraform-modules

# Terraform Modules Skill

Design and build production-ready, reusable Terraform modules following industry best practices.

## Module Structure

```
my-module/
├── main.tf           # Primary resources
├── variables.tf      # Input declarations
├── outputs.tf        # Output declarations
├── versions.tf       # Provider requirements
├── locals.tf         # Computed values
├── README.md         # Documentation
├── examples/
│   ├── basic/
│   └── complete/
└── tests/
    └── module_test.go
```

## Quick Start Template

### versions.tf
```hcl
terraform {
  required_version = ">= 1.5.0"

  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = ">= 5.0, < 6.0"
    }
  }
}
```

### variables.tf
```hcl
variable "name" {
  type        = string
  description = "Resource name prefix"

  validation {
    condition     = length(var.name) <= 32
    error_message = "Name must be 32 characters or less."
  }
}

variable "environment" {
  type        = string
  description = "Deployment environment"

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

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

### main.tf
```hcl
locals {
  common_tags = merge(var.tags, {
    Module      = "my-module"
    Environment = var.environment
  })
}

resource "aws_resource" "main" {
  name = var.name
  tags = local.common_tags
}
```

### outputs.tf
```hcl
output "id" {
  description = "Resource ID"
  value       = aws_resource.main.id
}

output "arn" {
  description = "Resource ARN"
  value       = aws_resource.main.arn
}
```

## Input Patterns

### Required vs Optional
```hcl
# Required - no default
variable "vpc_id" {
  type        = string
  description = "VPC ID (required)"
}

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

# Optio