Online Auction

Difficulty: Medium

What It Tests

Real-time bidding, concurrency control, fairness, consistency.

Topics Covered

• Distributed Locking
• Real-time Updates
• CAP Theorem & Consistency Models
• Distributed Transactions & Idempotency
• Message Queues & Async Processing

Hello Interview Breakdown

Read the full Hello Interview breakdown →

Video Walkthroughs

• Hello Interview: Online Auction & Bidding Service →
• Hello Interview: Online Auction — Meta Interview (5+ Approaches) →

Approach Hints

• Use optimistic locking on the current bid price (compare-and-swap)
• Broadcast new bids via WebSocket to all auction watchers
• Store bid history in an append-only event log
• Finalize auction close with a distributed lock to prevent last-second race conditions