Design a Real-Time Chess Service
Company: OpenAI
Role: Backend Engineer
Category: System Design
Difficulty: medium
Interview Round: Technical Screen
Design an online chess service that supports real-time two-player games.
The system should allow users to create or join a chess game, make legal moves, see the opponent's moves with low latency, and finish games by checkmate, timeout, resignation, draw, or abandonment.
Focus especially on:
1. How to represent and persist game state.
2. How to validate and order moves correctly.
3. How to track each player's remaining clock time accurately.
4. How to recover when a client disconnects, crashes, or reconnects from another device.
5. How to scale the service to many concurrent games while preserving correctness.
Assume real-time play is required, so moves should usually reach the opponent in under a few hundred milliseconds. State any additional assumptions you need.
Quick Answer: This question evaluates a candidate's ability to design scalable, correct real-time backend systems for multiplayer games, covering state modeling and persistence, move ordering and validation, clock management, fault recovery, and low-latency messaging; it falls under the System Design category and tests backend and distributed systems knowledge.