OpenAI & Meta Senior/Staff System Design Mock Interview: Design Online Auction

Designing an Instagram auction post feature requires balancing strong consistency for bid processing with low-latency real-time updates for viewers. The system must handle high read volumes while ensuring that bid submissions remain atomic, typically achieved through database transactions. Real-time bid updates rely on Server-Sent Events (SSE) and PubSub mechanisms to provide immediate feedback to users without excessive polling. Managing auction expiration and winner notification necessitates robust scheduling, moving from simple cron jobs to queue-based processing or durable execution platforms like Temporal. These tools ensure fault tolerance and reliability, particularly when handling high-stakes bids where data loss or missed notifications are unacceptable. The design emphasizes scalability, utilizing independent services for auction creation and streaming to maintain performance under heavy load while ensuring that the highest bid remains accurately reflected across the system.