System design interview question
Design a Global Real-Time Feed System for a Social Network (Like Twitter/X Timeline)
Design a system that serves personalized, real-time feeds to 500M monthly active users across 150 countries, where users follow up to 5,000 accounts and generate 100M posts per day. The system must deliver feed updates with <500ms latency, support timeline reads at 10M QPS (Read-Heavy), timeline writes at 100K QPS, and handle viral tweets that spike to 1M interactions per second. The feed must respect follower relationships, muting/blocking, content moderation policies, and ensure chronological consistency with eventual consistency trade-offs. Design the full stack including feed generation, ranking, caching, persistence, and real-time notifications.
Practice this question step by step with an AI interviewer that reviews your requirements, your architecture and your trade-offs, and scores the design.