chapter fourteen

14 Design a text messaging app

 

This chapter covers

  • Designing an app for billions of clients to send short messages
  • Considering approaches that trade off latency vs. cost
  • Designing for fault-tolerance

Let’s design a text messaging app, a system for 100K users to send messages to each other within seconds. Do not consider video or audio chat. Users send messages at an unpredictable rate, so our system should be able to handle these traffic surges. This is the first example system in this book that considers exactly-once delivery. Messages should not be lost, nor should they be sent more than once.

14.1 Requirements

After some discussion, we determined the following functional requirements:

14.2 Initial thoughts

14.3 Initial high-level design

14.4 Connection service

14.4.1 Making connections

14.4.2 Sender blocking

14.5 Sender service

14.5.1 Sending a message

14.5.2 Other discussions

14.6 Message service

14.7 Message-sending service

14.7.1 Introduction

14.7.2 High-level architecture

14.7.3 Steps in sending a message

14.7.4 Some questions

14.7.5 Improving availability

14.8 Search

14.9 Logging, monitoring, and alerting

14.10 Other possible discussion topics

Summary