Design Online Chess Matchmaking
Company: OpenAI
Role: Software Engineer
Category: System Design
Difficulty: hard
Interview Round: Technical Screen
Design the backend architecture for an online chess platform's matchmaking system.
Players submit requests to play ranked or casual chess games. A request may include the player ID, current rating, desired time control, region or latency constraints, client version, and optional preferences such as avoiding recent opponents. The system should pair players with compatible skill and acceptable latency, while gradually widening the search criteria as a player waits longer.
Focus on the following areas:
- Why the match request handler and the matchmaking service should be separate services.
- How match requests are queued and mapped to matchmaking workers.
- How a matchmaking service consumes widened bucket queues as wait time increases.
- What the player service owns and how it interacts with matchmaking.
- How to handle concurrency, duplicate requests, cancellation, failures, fairness, scalability, and observability.
Quick Answer: This question evaluates a candidate's ability to design scalable, low-latency matchmaking backend systems, covering distributed service decomposition, queuing and worker mapping, state ownership, progressive widening of search criteria, and concerns like concurrency, duplicate requests, cancellations, failures, fairness, scalability, and observability. It is commonly asked to assess architectural trade-offs in real-time distributed systems and the capability to apply system design principles to operational requirements; category: System Design; level of abstraction: practical application grounded in conceptual architectural understanding.