Design an online auction system

Q: Design an online auction system

This question evaluates system design skills—scalable distributed architecture, real-time messaging and push, concurrency and consistency under contention, API and data-model design, throughput estimation, and partitioning strategies—and is categorized under System Design.

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Question

Design a scalable online auction service.

Users can:

Create an auction (item info, start/end time, reserve price optional).
Place bids while the auction is live.
See the current winning bid and bid history.
Receive near-real-time notifications when the winning bid changes and when the auction ends.

Design goals and constraints:

Many auctions run concurrently; bids can spike near the end.
Correctness: determine the winner unambiguously; prevent accepting bids after the end time.
Low latency for bid placement and for notifying watchers.
The system should scale horizontally.

What APIs, data model, storage, messaging/pub-sub, and real-time push mechanism would you use? Include a rough QPS/throughput estimation approach and how you would partition/shard data (e.g., by auctionId).

Design an online auction system

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