In today's digital era, ensuring high availability and fault tolerance for applications is paramount. AWS offers robust tools and services to help achieve these goals, making it possible to build resilient, scalable, and secure infrastructure. This blog will walk you through the design and implementation of a custom Virtual Private Cloud (VPC) infrastructure on AWS, focusing on fault tolerance and high availability across multiple Availability Zones (AZs).

Introduction
Creating a fault-tolerant architecture means designing systems that continue to operate even when some components fail. By leveraging AWS services such as VPC, subnets, Internet Gateway (IGW), NAT Gateway, Elastic Load Balancer (ALB), and Auto Scaling Groups, you can build a highly resilient infrastructure that ensures your applications remain available and performant.

Project Overview
The primary objective of this project is to set up a custom VPC with the following key components:

1. VPC: A custom VPC with a defined CIDR block.
2. Subnets: Two public subnets and two private subnets spread across two different Availability Zones (AZs) to ensure high availability.
3. Internet Gateway (IGW): Provides internet access to resources in the public subnets.
4. NAT Gateway: Allows instances in the private subnets to access the internet securely for updates and patches.
5. Route Tables: Separate route tables for public and private subnets to manage traffic routing.
6. Elastic Load Balancer (ALB): Distributes incoming traffic across multiple instances in different AZs.
7. Auto Scaling Group: Manages and scales instances in the private subnets automatically based on demand.

Architecture Design

Multi-AZ Deployment

Distributing resources across multiple AZs enhances fault tolerance by ensuring that an outage in one AZ doesn't bring down the entire system. This architecture includes:

Public Subnets: Two public subnets located in different AZs.
Private Subnets: Two private subnets located in different AZs.

Internet Gateway and NAT Gateway

An Internet Gateway is attached to the VPC to facilitate inbound and outbound internet traffic for public-facing resources. A NAT Gateway is deployed in one of the public subnets to provide internet access to instances in the private subnets, ensuring they can download updates and patches securely without exposing them directly to the internet.

Route Tables

Two separate route tables are configured:

Public Route Table: Directs traffic from public subnets to the Internet Gateway.
Private Route Table: Routes traffic from private subnets to the NAT Gateway.

Elastic Load Balancer (ALB)

The ALB is deployed in the public subnets across multiple AZs, distributing incoming traffic to healthy instances. This setup ensures continuous availability and load distribution, even if an instance or an AZ fails.

Auto Scaling Group

The Auto Scaling Group launches instances in the private subnets, ensuring that the application scales automatically based on demand. By spreading instances across multiple AZs, the architecture can withstand AZ-level failures and maintain the desired capacity.

Fault Tolerance Features

1. Multi-AZ Distribution: By deploying resources in multiple AZs, the architecture can handle the failure of an entire AZ without affecting the application's availability.
2. Elastic Load Balancer: The ALB automatically routes traffic to healthy instances. If an instance or an AZ fails, the ALB reroutes traffic to instances in other AZs.
3. Auto Scaling Group: Ensures that the application maintains the required number of instances, launching new ones in different AZs if some instances fail.
4. NAT Gateway: Using multiple NAT Gateways in different AZs can enhance fault tolerance, ensuring continuous internet access for instances in private subnets even if one NAT Gateway fails. Benefits of the Architecture
5. Scalability: The Auto Scaling group adjusts the number of running instances based on demand, ensuring optimal resource usage.
6. High Availability: The multi-AZ deployment ensures that the application remains available even in the event of an AZ failure.
7. Security: The separation of public and private subnets enhances security by restricting internet access to internal resources.
8. Cost Efficiency: By automatically adjusting resources based on demand, the architecture helps minimize costs while maintaining performance.

Get the complete code here.

Procedures for Using Terraform Commands

Terraform is a powerful tool for managing infrastructure as code. By following these steps, you can efficiently create, manage, and destroy AWS infrastructure using Terraform. Below are the key procedures and commands you'll use:

Step 1: Initialize the Project
Initialize your Terraform project to download the necessary provider plugins.

terraform init

Step 2: Validate the Configuration
Validate your Terraform files to ensure there are no syntax errors.

terraform validate

Step 3: Plan the Infrastructure Changes
Generate an execution plan to see what changes Terraform will make to your infrastructure.

terraform plan

Step 4: Apply the Infrastructure Changes
Apply the changes specified in the execution plan to create or update your infrastructure.

terraform apply

Step 5: Destroy the Infrastructure
When you no longer need the infrastructure, you can destroy it using:

terraform destroy

Conclusion
Building a resilient and scalable VPC infrastructure on AWS involves leveraging various AWS services and best practices to ensure high availability and fault tolerance. By distributing resources across multiple AZs, utilizing load balancing, and implementing auto-scaling, you can create a robust environment capable of handling failures gracefully and maintaining continuous operation.

This architecture is an excellent foundation for deploying secure, scalable, and highly available applications on AWS, ensuring that your infrastructure can adapt to changing demands and withstand unexpected failures.