System design interview question
Design a Real-time Notification System for a Social Media Platform
Design a notification delivery system for a social media platform with 1M active users. The system must deliver notifications in real-time when users receive messages, likes, comments, or follower updates. You should expect approximately 100K notifications per second during peak hours. The system must guarantee that notifications are delivered to online users within 2 seconds, persist undelivered notifications for offline users (who may reconnect within 24 hours), and allow users to receive notifications across multiple devices simultaneously. Consider how you would handle scenarios where a single popular post generates millions of notifications, and how the system scales as user base grows.
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