Design an online auction system

Q: Design an online auction system

This question evaluates the ability to design a scalable, low-latency real-time auction platform, assessing competencies in distributed systems, consistency and concurrency control, data modeling, API design, real-time messaging and fanout, payments, and fraud detection.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at Meta.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Meta during technical interviews.

Question

System Design: Real-Time Online Auction Platform

You are asked to design an online auction system that supports real-time bidding at web scale. Assume a mix of desktop and mobile clients, global users, and many concurrent auctions.

Functional Requirements

Listing lifecycle: create, view, edit (before first valid bid), cancel (with restrictions), close.
Bidding: real-time bids, enforced minimum increments, reserve prices, buy-it-now, and anti-sniping protections.
Closeout: determine winner, collect payment, notify parties, and finalize auction state.
Real-time updates: push current price, bid events, reserve met status, time-left/extension, and closeout results to watchers.

Non-Functional Requirements

High availability and scalability across many concurrent auctions and watchers.
Strong consistency for winner determination and money-related state.
Low-latency bid processing and fanout (<200–300 ms p95 event-to-update as a target).
Observability, fraud detection, and reliable payments/settlement.

Deliverables

APIs (HTTP and real-time) for listings, bids, and buy-it-now.
Data model (schemas/entities, indexes) and event model.
Consistency model for winning bids and concurrency control strategy.
Real-time update design (WebSocket/streaming), ordering, and backpressure.
Anti-sniping policy and auction closeout flow.
Fraud detection hooks and controls.
Payments and settlement flows with idempotency.
Scalability, fault tolerance, and monitoring strategy.

Assume minimal context as needed (e.g., auctions are priced in a single currency; times are UTC).

Design an online auction system

Quick Overview

System Design: Real-Time Online Auction Platform

Functional Requirements

Non-Functional Requirements

Deliverables

Solution

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