Terraform Module Library

From the author

Build reusable Terraform modules for AWS, Azure, GCP, and OCI infrastructure following infrastructure-as-code best practices. Use when creating infrastructure modules, standardizing cloud provisioning, or implementing reusable IaC components.

— the description by Seth Hobson

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a standardized framework for developing, structuring, and testing Terraform modules. It emphasizes infrastructure-as-code best practices, including modular design, input validation, semantic versioning, and automated testing with Terratest. By following these patterns, teams can create consistent, multi-cloud compatible infrastructure components that are easier to maintain, document, and compose into larger systems.

What it does

Defines a standard directory structure for Terraform modules
Provides patterns for input variables, outputs, and provider versioning
Outlines best practices for resource tagging and conditional logic
Demonstrates how to implement automated testing using Terratest
Offers guidance on module composition for complex infrastructure
Includes specific architectural patterns for AWS and OCI services

When to use it

When you need to standardize cloud provisioning across your organization
When building reusable infrastructure components for multi-cloud environments
When you want to enforce infrastructure-as-code best practices
When creating complex infrastructure that requires modular composition
When establishing a library of tested, production-ready cloud modules

Advantages

Promotes consistency and reusability across cloud providers
Simplifies maintenance through modular design and documentation
Ensures higher quality infrastructure via automated testing
Facilitates easier scaling of cloud resources
Reduces configuration drift through standardized patterns

Usage examples

“How should I structure a new Terraform module for AWS?”: The agent provides the recommended directory layout, including folders for main.tf, variables.tf, outputs.tf, examples, and tests.
“What are the best practices for validating input variables in Terraform?”: The agent explains the use of validation blocks with regex conditions to ensure input data integrity.
“How can I test my Terraform module using Terratest?”: The agent provides a Go-based test example that initializes, applies, and validates module outputs.
“Show me how to compose multiple Terraform modules together.”: The agent demonstrates how to pass outputs from one module (e.g., a VPC) as inputs to another (e.g., an RDS instance).

Install

Download the skill as a ZIP:
https://mp-staging.autogineer.com/agent-skills/wshobson/terraform-module-library/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip terraform-module-library.zip -d .agents/skills

Documentation by Seth Hobson

Production-ready Terraform module patterns for AWS, Azure, GCP, and OCI infrastructure.

Purpose

Create reusable, well-tested Terraform modules for common cloud infrastructure patterns across multiple cloud providers.

When to Use

Build reusable infrastructure components
Standardize cloud resource provisioning
Implement infrastructure as code best practices
Create multi-cloud compatible modules
Establish organizational Terraform standards

Module Structure

terraform-modules/
├── aws/
│   ├── vpc/
│   ├── eks/
│   ├── rds/
│   └── s3/
├── azure/
│   ├── vnet/
│   ├── aks/
│   └── storage/
├── gcp/
│   ├── vpc/
│   ├── gke/
│   └── cloud-sql/
└── oci/
    ├── vcn/
    ├── oke/
    └── object-storage/

Standard Module Pattern

module-name/
├── main.tf          # Main resources
├── variables.tf     # Input variables
├── outputs.tf       # Output values
├── versions.tf      # Provider versions
├── README.md        # Documentation
├── examples/        # Usage examples
│   └── complete/
│       ├── main.tf
│       └── variables.tf
└── tests/           # Terratest files
    └── module_test.go

AWS VPC Module Example

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

resource "aws_subnet" "private" {
  count             = length(var.private_subnet_cidrs)
  vpc_id            = aws_vpc.main.id
  cidr_block        = var.private_subnet_cidrs[count.index]
  availability_zone = var.availability_zones[count.index]

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

resource "aws_internet_gateway" "main" {
  count  = var.create_internet_gateway ? 1 : 0
  vpc_id = aws_vpc.main.id

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

variables.tf:

variable "name" {
  description = "Name of the VPC"
  type        = string
}

variable "cidr_block" {
  description = "CIDR block for VPC"
  type        = string
  validation {
    condition     = can(regex("^([0-9]{1,3}\\.){3}[0-9]{1,3}/[0-9]{1,2}$", var.cidr_block))
    error_message = "CIDR block must be valid IPv4 CIDR notation."
  }
}

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

variable "private_subnet_cidrs" {
  description = "CIDR blocks for private subnets"
  type        = list(string)
  default     = []
}

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

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

outputs.tf:

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

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

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

Best Practices

Use semantic versioning for modules
Document all variables with descriptions
Provide examples in examples/ directory
Use validation blocks for input validation
Output important attributes for module composition
Pin provider versions in versions.tf
Use locals for computed values
Implement conditional resources with count/for_each
Test modules with Terratest
Tag all resources consistently

Reference: See references/aws-modules.md and references/oci-modules.md

Module Composition

module "vpc" {
  source = "../../modules/aws/vpc"

  name               = "production"
  cidr_block         = "10.0.0.0/16"
  availability_zones = ["us-west-2a", "us-west-2b", "us-west-2c"]

  private_subnet_cidrs = [
    "10.0.1.0/24",
    "10.0.2.0/24",
    "10.0.3.0/24"
  ]

  tags = {
    Environment = "production"
    ManagedBy   = "terraform"
  }
}

module "rds" {
  source = "../../modules/aws/rds"

  identifier     = "production-db"
  engine         = "postgres"
  engine_version = "15.3"
  instance_class = "db.t3.large"

  vpc_id     = module.vpc.vpc_id
  subnet_ids = module.vpc.private_subnet_ids

  tags = {
    Environment = "production"
  }
}

Testing

// tests/vpc_test.go
package test

import (
    "testing"
    "github.com/gruntwork-io/terratest/modules/terraform"
    "github.com/stretchr/testify/assert"
)

func TestVPCModule(t *testing.T) {
    terraformOptions := &terraform.Options{
        TerraformDir: "../examples/complete",
    }

    defer terraform.Destroy(t, terraformOptions)
    terraform.InitAndApply(t, terraformOptions)

    vpcID := terraform.Output(t, terraformOptions, "vpc_id")
    assert.NotEmpty(t, vpcID)
}

multi-cloud-architecture - For architectural decisions
cost-optimization - For cost-effective designs

Files

ATTRIBUTION.mdAdded by AutoGineer1012 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md5.5 KiB
references/aws-modules.md1.3 KiB
references/oci-modules.md1.4 KiB

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

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Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download terraform-module-library.zip