🏗️ AWS VPC Terraform Module

Modular Terraform configuration that provisions an AWS Virtual Private Cloud (VPC) with public and private subnets, internet egress, and optional high-availability NAT gateways. The module supports both single-Availability Zone and multi-Availability Zone topologies, making it a reusable foundation for infrastructure projects.

✨ Highlights

• Creates a VPC, public and private subnets, routing, and egress components in one apply.
• Switches between single-AZ and multi-AZ deployments with a boolean flag.
• Supports one shared NAT Gateway (cost-optimized) or one per AZ (high availability).
• Allows custom CIDR blocks, AZ selections, and resource naming.
• Exposes outputs for downstream modules (subnet IDs, NAT IDs, and more).

🖼️ Visual Overview

Single-AZ layout	Multi-AZ layout

• The single-AZ deployment keeps costs low while still providing separate public and private tiers.
• Multi-AZ mode scales the same topology across several AZs for higher availability.

🗂️ Repository Layout

• main.tf roots the example deployment in eu-central-1 and consumes the module.
• modules/awsvpc contains the reusable module logic and variable definitions.
• TerraformVisual/ holds topology diagrams and Terraform plan outputs for reference.
• output.tf surfaces the module outputs from the example configuration.

🧰 Prerequisites

• Terraform 1.5.7 or newer (module tested with Terraform 1.5.7).
• AWS credentials exported in your shell or configured through the AWS CLI.
• Appropriate IAM permissions to create networking resources (VPC, subnets, EIPs, NAT, IGW).

🚀 Quick Start

• terraform init to download providers and configure the backend.
• terraform plan to review the changes in your target account.
• terraform apply to create the VPC (answer yes when prompted).
• terraform destroy when you want to remove all provisioned resources.

🧪 Example Usage

provider "aws" {
  region = "eu-central-1"
}

module "vpc" {
  source              = "./modules/awsvpc"
  vpc_name            = "platform-vpc"
  vpc_cidr            = "10.0.0.0/16"
  single_az           = false
  availability_zones  = ["eu-central-1a", "eu-central-1b", "eu-central-1c"]
  egress_multi_nat_gw = true
}

• Set single_az = true to restrict the deployment to the first AZ in availability_zones.
• Toggle egress_multi_nat_gw to control whether a NAT Gateway is created per public subnet.

⚙️ Configuration Reference

Input	Description	Type	Default
vpc_name	Name tag applied to the VPC resource.	string	"VPC-test1"
vpc_cidr	Base CIDR block for the VPC (supports /16).	string	"10.0.0.0/16"
single_az	Deploy a single-AZ topology when true.	bool	true
availability_zones	Ordered list of AZs used for subnet placement.	list(string)	["eu-central-1a", "eu-central-1b", "eu-central-1c"]
egress_multi_nat_gw	Create a NAT Gateway per public subnet when true.	bool	false

Output	Description
vpc_id	Identifier of the created VPC.
subnet_ids	Map containing lists of public and private subnet IDs.
public_subnet_ids	List of IDs for every public subnet.
private_subnet_ids	List of IDs for every private subnet.
internet_gateway_id	ID of the provisioned Internet Gateway.
nat_gateway_ids	List of NAT Gateway IDs created by the deployment.

🧭 Architecture Modes

• Single AZ: Creates one /24 public subnet and one /19 private subnet in the first AZ supplied. Internet access for private workloads is routed through a single NAT Gateway. See the single-AZ diagram in the visual overview above.
• Multi AZ: Creates a pair of public/private subnets in each AZ listed. NAT egress scales from one shared gateway to one per AZ depending on egress_multi_nat_gw. See the multi-AZ diagram in the visual overview above.

🛡️ NAT Gateway Strategies

• Cost optimized: Keep egress_multi_nat_gw = false to deploy one NAT Gateway regardless of the number of AZs.
• High availability: Set egress_multi_nat_gw = true to match the number of NAT Gateways to the number of public subnets.
• Remember that NAT Gateways incur hourly and data processing charges; destroy unused environments to limit spend.

🛠️ Troubleshooting Tips

• Ensure the availability_zones list matches the selected AWS region; invalid AZ labels cause planning errors.
• When changing between single-AZ and multi-AZ modes, run terraform apply twice if Terraform needs to recreate route associations.
• Use terraform state list to inspect created resources when debugging or before destroying the stack.

📄 License

Licensed under the Apache 2.0 License. See LICENSE for full details.