terraform-module-builder

What this skill does

# Terraform Module Builder

Build reusable, production-ready Terraform modules for cloud infrastructure.

## Core Workflow

1. **Define module structure**: Organize files properly
2. **Declare variables**: Input parameters with validation
3. **Create resources**: Infrastructure definitions
4. **Configure outputs**: Export useful values
5. **Setup state**: Remote backend configuration
6. **Document**: README and examples

## Module Structure

```
modules/
└── vpc/
    ├── main.tf           # Primary resources
    ├── variables.tf      # Input variables
    ├── outputs.tf        # Output values
    ├── versions.tf       # Provider versions
    ├── locals.tf         # Local values
    ├── data.tf           # Data sources
    ├── README.md         # Documentation
    └── examples/
        └── complete/
            ├── main.tf
            └── outputs.tf
```

## VPC Module Example

### Main Configuration

```hcl
# modules/vpc/main.tf

resource "aws_vpc" "main" {
  cidr_block           = var.cidr_block
  enable_dns_hostnames = var.enable_dns_hostnames
  enable_dns_support   = var.enable_dns_support

  tags = merge(
    var.tags,
    {
      Name = var.name
    }
  )
}

resource "aws_internet_gateway" "main" {
  count = var.create_igw ? 1 : 0

  vpc_id = aws_vpc.main.id

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

resource "aws_subnet" "public" {
  count = length(var.public_subnets)

  vpc_id                  = aws_vpc.main.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 = "${var.name}-public-${var.availability_zones[count.index]}"
      Tier = "public"
    }
  )
}

resource "aws_subnet" "private" {
  count = length(var.private_subnets)

  vpc_id            = aws_vpc.main.id
  cidr_block        = var.private_subnets[count.index]
  availability_zone = var.availability_zones[count.index]

  tags = merge(
    var.tags,
    {
      Name = "${var.name}-private-${var.availability_zones[count.index]}"
      Tier = "private"
    }
  )
}

resource "aws_eip" "nat" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.public_subnets)) : 0

  domain = "vpc"

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

  depends_on = [aws_internet_gateway.main]
}

resource "aws_nat_gateway" "main" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.public_subnets)) : 0

  allocation_id = aws_eip.nat[count.index].id
  subnet_id     = aws_subnet.public[count.index].id

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

  depends_on = [aws_internet_gateway.main]
}

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.main.id

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

resource "aws_route" "public_internet" {
  count = var.create_igw ? 1 : 0

  route_table_id         = aws_route_table.public.id
  destination_cidr_block = "0.0.0.0/0"
  gateway_id             = aws_internet_gateway.main[0].id
}

resource "aws_route_table_association" "public" {
  count = length(var.public_subnets)

  subnet_id      = aws_subnet.public[count.index].id
  route_table_id = aws_route_table.public.id
}

resource "aws_route_table" "private" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.private_subnets)) : 0

  vpc_id = aws_vpc.main.id

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

resource "aws_route" "private_nat" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.private_subnets)) : 0

  route_table_id         = aws_route_table.private[count.index].id
  destination_cidr_block = "0.0.0.0/0"
  nat_gateway_id         = aws_nat_gateway.main[var.single_nat_gateway ? 0 : count.index].id
}

resource "aws_route_table_association" "private" {
  count = length(var.private_subnets)

  subnet_id      = aws_subnet.private[count.index].id
  route_table_id = aws_route_table.private[var.single_nat_gateway ? 0 : count.index].id
}
```

### Variables

```hcl
# modules/vpc/variables.tf

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

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

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

  validation {
    condition     = can(cidrhost(var.cidr_block, 0))
    error_message = "Must be a valid CIDR block."
  }
}

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

variable "public_subnets" {
  description = "List of public subnet CIDR blocks"
  type        = list(string)
  default     = []

  validation {
    condition     = alltrue([for cidr in var.public_subnets : can(cidrhost(cidr, 0))])
    error_message = "All public subnets must be valid CIDR blocks."
  }
}

variable "private_subnets" {
  description = "List of private subnet CIDR blocks"
  type        = list(string)
  default     = []
}

variable "enable_dns_hostnames" {
  description = "Enable DNS hostnames in the VPC"
  type        = bool
  default     = true
}

variable "enable_dns_support" {
  description = "Enable DNS support in the VPC"
  type        = bool
  default     = true
}

variable "create_igw" {
  description = "Create Internet Gateway"
  type        = bool
  default     = true
}

variable "enable_nat_gateway" {
  description = "Enable NAT Gateway for private subnets"
  type        = bool
  default     = true
}

variable "single_nat_gateway" {
  description = "Use a single NAT Gateway (cost savings)"
  type        = bool
  default     = false
}

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

### Outputs

```hcl
# modules/vpc/outputs.tf

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

output "vpc_cidr_block" {
  description = "The CIDR block of the VPC"
  value       = aws_vpc.main.cidr_block
}

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

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

output "public_subnet_cidr_blocks" {
  description = "List of public subnet CIDR blocks"
  value       = aws_subnet.public[*].cidr_block
}

output "private_subnet_cidr_blocks" {
  description = "List of private subnet CIDR blocks"
  value       = aws_subnet.private[*].cidr_block
}

output "nat_gateway_ids" {
  description = "List of NAT Gateway IDs"
  value       = aws_nat_gateway.main[*].id
}

output "internet_gateway_id" {
  description = "The ID of the Internet Gateway"
  value       = try(aws_internet_gateway.main[0].id, null)
}
```

### Versions

```hcl
# modules/vpc/versions.tf

terraform {
  required_version = ">= 1.0"

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

## Remote State Configuration

```hcl
# backend.tf

terraform {
  backend "s3" {
    bucket         = "my-terraform-state"
    key            = "production/vpc/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }
}

# State locking table
resource "aws_dynamodb_table" "terraform_locks" {
  name         = "terraform-locks"
  billing_mode = "PAY_PER_REQUEST"
  hash_key     = "LockID"

  attribute {
    name = "LockID"
    type = "S"
  }
}
```

## EKS Module Example

```hcl
# modules/eks/main.tf

resource "aws_eks_cluster" "main" {
  name     = var.cluster_name
  version  = var.cluster_version
  role_arn = aws_iam_role.cluster.arn

  vpc_config {
    subne