Building a Scalable and Resilient E-Commerce Application: MyClothes.com

In this section, we transition from a stateless web application (WhatIsTheTime.com) to a stateful e-commerce platform (MyClothes.com). This introduces new challenges, such as maintaining user sessions, ensuring high availability, and scaling efficiently.

Challenges in a Stateful Web Application

MyClothes.com needs to handle:

✅ Hundreds of concurrent users navigating and adding items to a shopping cart.

✅ Session persistence to prevent users from losing their cart when requests are routed to different servers.

✅ Horizontal scalability, ensuring the web application remains stateless wherever possible.

✅ Secure and efficient data storage, including user details and shopping cart information.

Initial Architecture & Its Problem

The architecture follows a standard multi-AZ setup:

1. User requests go through Route 53 (DNS).
2. Requests are distributed by an ELB (Elastic Load Balancer).
3. ELB forwards requests to EC2 instances within an Auto Scaling Group.

💥 The issue? Each request may hit a different EC2 instance, causing users to lose their shopping cart as there’s no centralized session management.

Solving the Shopping Cart Problem

Solution 1: ELB Stickiness (Session Affinity)

• How it works:
  • ELB routes requests from the same user to the same EC2 instance.
  • Users retain their cart as long as the instance remains active.
• Limitations:
  • If the EC2 instance fails or is replaced, the session is lost.
  • This doesn’t fully solve our scalability issue.

Solution 2: Web Cookies (Client-Side Storage)