← Meta Interview Insights

Meta·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Jul 2026

Summary

Meta system design round, got asked to build an eBay-style auction platform from scratch. Scope was clearly defined upfront which was nice, but there's a lot of surface area here and I felt like I was constantly triaging what to go deep on.

Questions Asked (1)

Q1

Design an online auction system similar to eBay, where users can create auctions with a start and end time, place bids, and have the winner determined automatically when the auction closes.

System DesignTechnical Trade-offsData Modeling
Author's notes

The core design wasn't too bad to sketch out but the race condition piece is where I got stuck.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying functional and non-functional requirements, then estimate scale (users, auctions, bids per second). Design the data model and high-level architecture, focusing on how to handle bid concurrency and automatic auction closing reliably.

Pro tip: Emphasize idempotency and exactly-once processing for bid placement and auction closing, as these are critical in a distributed auction system to prevent double bids or missed winners.

1. Clarify Requirements and Scale

Ask about expected user base, auction volume, bid rate, latency requirements, and consistency needs. Define core features: create auction, place bid, auto-close, determine winner.

2. Design Data Model

Define entities: User, Auction (with start/end time, status), Bid (with amount, timestamp, bidder). Consider indexes for efficient queries like highest bid per auction.

3. High-Level Architecture

Outline components: API servers, auction service, bid service, database (SQL for transactions or NoSQL for scale), cache, message queue for async processing, and a scheduler for auction closing.

4. Handle Concurrency and Consistency

Discuss strategies for bid concurrency: optimistic locking, distributed locks, or serializable transactions. Ensure bids are processed in order and only valid bids accepted.

5. Auction Closing and Winner Determination

Design a reliable mechanism to close auctions at end time: use a distributed scheduler (e.g., cron with leader election) or delay queue. Ensure exactly-once processing and notify winner.

Key Points to Mention

  • Use of database transactions or optimistic concurrency control to handle simultaneous bids and prevent race conditions.
  • Sharding strategy for auctions and bids to scale horizontally (e.g., by auction ID).
  • Caching of hot auction data (e.g., current highest bid) to reduce database load.
  • Asynchronous processing of bid validation and auction closing via message queues for scalability and reliability.
  • Idempotency keys for bid placement to avoid duplicate bids due to retries.
  • Monitoring and alerting for auction closing failures and bid processing latency.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.