Scaling to support over a million users online in a single server is a remarkable achievement, and Discord's engineering team has pushed the boundaries to make it possible. This article from the Discord blog details the challenges, innovations, and technical strategies employed to handle such massive scale, offering insights into the architecture and optimizations that enable seamless communication for millions of users simultaneously.

https://discord.com/blog/maxjourney-pushing-discords-limits-with-a-million-plus-online-users-in-a-single-server