Apple system design interview questions

Which levels get a design round

Design questions candidates report

• Design photo sync across devices

  How to design a cloud file storage and sync service like Google Drive or Dropbox: requirements, storage and traffic math, splitting files into content-addressed blocks, resumable uploads and deduplication, separating metadata from blobs, a change journal with cursors so every device syncs, push notifications, conflict handling and version history, sharing permissions, and the trade-offs.

  Full walkthrough: Google Drive Practise on the design board

• Design message delivery

  A LADDER walkthrough of a mobile chat system: requirements, scale math for 20 billion messages a day and 200 million open connections, the WebSocket and REST API, a message store partitioned by conversation, then the deep dives: routing between chat servers, offline delivery and push, sent-delivered-read receipts, per-conversation ordering, group fan-out, presence, media and end-to-end encryption.

  Full walkthrough: WhatsApp Practise on the design board

• Design a push notification service

  How to design a shared notification service that any team can call: one API for push, SMS, email and in-app, user preferences and quiet hours, templates, separate priority queues so a marketing blast never delays a login code, per-provider rate limits, retries with backoff, deduplication, dead device tokens, bulk campaign fan-out and delivery tracking.

  Full walkthrough: Notification system

• Design a ticket booking system

  Design a ticket booking app where thousands of people fight over the same few hundred seats. Requirements and scale, the booking API and seat data model, then the hard parts: atomic multi-seat holds with expiry, optimistic versus pessimistic locking, tying payment to a hold without double booking, a virtual waiting room for blockbuster releases, live seat maps, and the trade-offs.

  Full walkthrough: Movie booking

• Design a peer-to-peer web crawler

  Design a crawler that fetches a billion pages a month without hammering any site. Requirements and scale, the control interfaces and URL table, the fetch-parse-enqueue loop, then the hard parts: a URL frontier with priority and per-host politeness queues, URL and content deduplication with Bloom filters and fingerprints, spider traps, recrawl scheduling, partitioning by host, and the trade-offs.

  Full walkthrough: Web crawler

Also reported

• Design an LLM agent that calls tools to finish a task

How to answer any design question: the LADDER method · How the design round is scored by level · Low-level design and machine coding

Questions people ask