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Design an Online Chess Service from Launch to Scale

OpenAISoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSystem Design

Last updated

This problem tests the ability to design a real-time, stateful gaming system, focusing on concurrency control, low-latency communication, and fault tolerance.

Design an Online Chess Service

Design an architecture for an online chess platform that supports real-time multiplayer games. The system should handle move validation, clock management, and matchmaking.

Functional Requirements

  1. Matchmaking: Connect two players of similar skill levels.
  2. Game State Management: Validate moves according to FIDE rules and track game time for both players.
  3. Persistence: Allow players to resume games after a temporary network disconnection.
  4. Real-time Updates: Ensure moves made by one player are reflected on the opponent's screen with minimal latency.

Non-Functional Requirements

  1. Consistency: Ensure no move is processed twice, and game state remains consistent even if a server node fails.
  2. Availability: The system should handle 100,000 concurrent games.
  3. Latency: Move updates should reach the opponent within 100ms.

Deliverables

  1. API Design: Define the primary interface for move submissions and game status polling.
  2. Architecture: Describe the choice of transport protocol (e.g., WebSockets vs. HTTP long-polling) and the communication flow.
  3. Concurrency: Explain how you handle the "simultaneous move" problem if both players submit a move at nearly the same time.
  4. Reliability: Describe how you persist the game state and ensure fairness if a player loses connection during their turn.

Hints

Hint 1

Consider using an actor-based model or a dedicated game-server service to encapsulate the state of a single chess match.

Hint 2

Think about how to use an incremental sequence number (or versioning) for every move to prevent race conditions during state updates.

Hint 3

Decide how to handle 'clock drift' and ensure that the server, not the client, is the ultimate authority on how much time has elapsed.

Follow-up questions

  • How would you implement a 'spectator' mode that allows thousands of users to watch a single grandmaster game without overwhelming the game server?
  • If you needed to add a turn-based move-validation engine that runs on a separate microservice, how would you ensure the latency budget is still met?
  • How would you detect and prevent 'engine cheating' where a user might be running a chess bot in the background?