Design a Chat System

Each one worked end to end: requirements, estimates, the first diagram, the bottleneck that appears at scale, and the two or three deep dives an interviewer will push you into.

This module is 07.3 of the 6 in Design Case Studies. It runs about 4 hours across 5 lessons, and closes with Presence — Hold a million live connections and deliver every message once, in order, including to the phone that was in a tunnel.