Terraform Module Library

Production-ready Terraform module patterns for AWS, Azure, and GCP 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/

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

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)

}

Related Skills

• multi-cloud-architecture

• For architectural decisions

• cost-optimization

• For cost-effective designs