Case Study: Real-Time Chat System

Overview

Design a WhatsApp-like chat system with WebSocket connections, message queuing, and delivery guarantees.

Real-time chat is one of the most challenging system design problems.

You will build 6 architecture steps that model production dependencies.

You will run 1 failure experiment to observe bottlenecks and recovery behavior.

Success target: Messages delivered in <100ms to online users, queued for offline users, zero message loss.

Learning Objectives

• Designed a real-time chat system with WebSocket and message queuing
• Understood presence tracking and connection management
• Learned about message delivery guarantees for chat
• Experienced the impact of delivery guarantee choices on user experience

Prerequisites

• Topic Hub: WebSocket
• Chapter 17: Case Study - Chat System
• Prior Lab: Async Processing with Message Queues
• Prior Lab: Load Balancing & Horizontal Scaling

Experiments

1. Change message delivery guarantee to at_most_once to see lost messages