System Design on AWS

Chapter 19. Designing a Chat Application

In Chapter 6, we explored multiple networking protocols and communication mechanisms for building near real-time messaging platforms. Messaging applications are widely used across the globe. The application can be standalone, such as WhatsApp or Telegram, or it can be integrated as a feature inside social networking apps like LinkedIn or Instagram. In this chapter, we’ll learn how to design large-scale messaging applications to offer fast communication in near real time. We’ll also discuss the underlying architecture of WhatsApp messenger, which serves a huge number of concurrent users. Let’s begin with the system requirements of a chat application.

System Requirements

A messaging application can support a wide variety of features, but to keep it simple, we will choose to build a limited set of functionalities and skip features like voice and video calling. Let’s finalize the requirements to answer these questions:

What kinds of communication are supported by the application?

The application offers one-to-one messaging, group messaging, and broadcast messaging. A broadcast is different from group messaging in that only a subset of users can send messages in the broadcast channel.

What type of content will be supported by the application?

The application allows users to share text messages, images, videos, and documents. The next question that arises is whether there is a limit to the video file size. To avoid large media uploads, ...