Design an online Chess Game that is fast, reliable, and supports 100 million monthly active users playing one game a week.

To design a scalable online chess game for 100 million MAU, we'd employ a distributed architecture. Key components include:

• Load Balancers: Distribute incoming traffic across multiple API servers.
• API Servers: Handle user requests, game creation, and move validation.
• Game Service: Manages game state, turn logic, and real-time updates. This service would likely be sharded by game ID or user ID for scalability.
• Pub/Sub System (e.g., Kafka, Redis Pub/Sub): Facilitates real-time communication between game servers and clients for move propagation and game state changes.
• Real-time Communication (e.g., WebSockets, HTTP Long Polling): Enables clients to receive immediate updates on game progress.
• Database: A NoSQL database (like Cassandra or DynamoDB) is suitable for storing user profiles, game history, and move data due to its horizontal scalability and ability to handle high write/read volumes. A write-through cache (e.g., Redis) would be used for frequently accessed game states to reduce database load and latency.