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Design chat and online chess

MicrosoftMachine Learning Engineer · Onsite
MediumMachine Learning EngineerOnsiteSystem Design

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This problem tests your ability to design a distributed system that supports low-latency, real-time interactions for both chat messaging and synchronized game state for a chess platform.

System Design: Real-time Chat and Online Chess

Design a global online chess platform that supports millions of concurrent users. The system must handle two primary features: real-time multiplayer chess games and a global chat system. Assume you are supporting 1 million daily active users (DAU) with a peak of 100,000 concurrent games.

Functional Requirements

  1. Chess Gameplay: Users can start a game, make moves that are validated in real-time, and view the game board state. Game state must be synchronized instantly for both players.
  2. Chat: Players can send messages in the game room, and global or public channels should be available.
  3. Game Persistence: Game history and final outcomes must be saved.

Non-Functional Requirements

  1. Low Latency: Chess moves should appear to the opponent within < 100ms.
  2. Reliability: A network flicker should not result in a lost game or state corruption.
  3. Scalability: The system should handle spikes in traffic during popular tournament events.

Deliverables

  • API Design: Define the primary endpoints and socket events for moves and chat.
  • Data Model: Propose a storage schema for game states, chat logs, and user profiles.
  • Architecture: Describe the components needed to maintain persistent connections (WebSockets vs. long polling) and handle the high frequency of game updates.
  • Trade-offs: Discuss the choice of database for game state (e.g., Redis vs. SQL) and how to handle consistency versus availability during network partitions.

Hints

Hint 1

Consider using a WebSocket-based architecture for full-duplex communication, but plan for a fallback mechanism for clients with poor connectivity.

Hint 2

For chess moves, use a fast, in-memory data structure for the current game state, and perform asynchronous writes to a persistent database to minimize latency.

Hint 3

Decouple the chat system from the game engine so that a surge in chat activity does not impact the performance of the game move validation logic.

Follow-up questions

  • How would you handle a user who disconnects mid-game and attempts to reconnect 30 seconds later?
  • If you needed to add a spectating feature for a grandmaster game with 50,000 concurrent viewers, how would you modify your architecture?
  • What metrics would you monitor to identify bottlenecks in the move validation process or latency spikes in the chat delivery?