Engineering Blog

Deep dives on how Code Arena is built.

• Designing a Fair Elo System for Coding Contests — Classic Elo is built for two players. Here's how Code Arena generalizes it to rate N-player coding contests and real-time matches fairly — using expected rank, geometric-mean targeting, damping, and a zero-sum correction.
• Building Code Arena: Scaling WebSockets & Docker Sandboxes for a Battle Royale — A deep dive into Code Arena's architecture: decoupling submission spikes with BullMQ, sandboxing untrusted code with Docker and cgroups, streaming verdicts over Redis pub/sub and per-user WebSockets, and orchestrating a real-time coding Battle Royale.