Terraform Module Library

by wshobson46891e7e60daNo licenseListed Oct 8, 2026Updated Oct 8, 2026

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.

Instructions onlyDevOps & Cloud

AI-generated overview

Guides creation of reusable Terraform modules for AWS, Azure, GCP and OCI infrastructure.

What it does: This skill provides patterns and conventions for building reusable Terraform modules covering common cloud infrastructure such as VPCs, Kubernetes clusters, databases and storage across AWS, Azure, GCP and OCI. It describes a standard module layout (main.tf, variables.tf, outputs.tf, versions.tf, examples and tests), shows a worked AWS VPC example with variables, outputs and validation, and lists best practices including semantic versioning, provider pinning, tagging and Terratest testing. It also covers module composition, where one module's outputs feed another's inputs. Two reference files cover AWS and OCI module details.
When to use it: Use it when creating reusable infrastructure modules, standardizing cloud resource provisioning across providers, or establishing organizational Terraform standards. It also fits teams implementing infrastructure-as-code best practices or building multi-cloud compatible components.
Requirements: Terraform and its HCL configuration language, plus cloud provider credentials for whichever of AWS, Azure, GCP or OCI is targeted. Testing examples rely on Go, Terratest and testify. The skill ships no scripts; it is instructions and reference documents only.

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/

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

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  )}

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     = {}}

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}

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

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"  }}

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.gopackage 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)}

// tests/vpc_test.gopackage 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

Source and attribution

Source:wshobson/agentsinplugins/cloud-infrastructure/skills/terraform-module-libraryat commit46891e7

License: No license

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Terraform Module Library

Terraform Module Library

Purpose

When to Use

Module Structure

Standard Module Pattern

AWS VPC Module Example

Best Practices

Module Composition

Testing

Related Skills

Source and attribution

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