Terraform Module Library
Module Structure
code
module-name/
├── main.tf # Main resources
├── variables.tf # Input variables
├── outputs.tf # Output values
├── versions.tf # Provider versions
├── examples/
│ └── complete/
│ ├── main.tf
│ └── variables.tf
└── tests/
└── 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 "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
}
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
}
Testing with Terratest
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)
}