Terraform Module Library

When to use this skill

Use Terraform Module Library when an AI agent needs a reusable SKILL.md workflow for this job: 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.

When not to use it

Skip Terraform Module Library when the task is outside the coding category, or when a more specific skill in this directory already covers the same workflow with clearer triggers.

How to install

1. Personal install: create ~/.claude/skills/terraform-module-library/SKILL.md (and any bundled scripts) so Claude Code, Claude Desktop, and compatible agents can load it in every project.
2. Project install: commit the same folder at .claude/skills/terraform-module-library/ so teammates get the skill with the repo.
3. Restart the agent session after copying files so it re-scans the skills directory, then ask for the task in words that match the skill description.

Full install guide for Claude, Cursor, and Codex

What this skill does

# Terraform Module Library

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:**

```hcl 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:**

```hcl 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:**

```hcl 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

1. **Use semantic versioning** for modules 2. **Document all variables** with descriptions 3. **Provide examples** in examples/ directory 4. **Use validation blocks** for input validation 5. **Output important attributes** for module composition 6. **Pin provider versions** in versions.tf 7. **Use locals** for computed values 8. **Implement conditional resources** with count/for_each 9. **Test modules** with Terratest 10. **Tag all resources** consistently

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

## Module Composition

```hcl 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

```go // 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) } ```

## Related Skills

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

Intended uses

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