Senior System Design Mock Interview: Design an e-commerce platform

Designing a scalable e-commerce platform requires balancing consistency for financial transactions with high availability for search and notifications. Inventory management relies on Redis-based soft reservations with a ten-minute time-to-live to prevent overselling while maintaining system performance. Price-drop notifications leverage Change Data Capture (CDC) to trigger asynchronous worker processes, ensuring efficient delivery to millions of subscribers without overloading the primary database. Real-time client updates are best handled through Server-Sent Events (SSE), which provide a lighter, more effective communication channel than WebSockets or polling. Scalability is further addressed through pagination of subscription lists and queue-based fan-out patterns. Monitoring system health involves tracking latency across event stages—from database updates to notification delivery—using centralized metrics to maintain performance standards for high-interest items like limited-edition product drops.