Apple System Design Questions

Design Cloud Photo Storage and Multi-Device Sync

Design a file (or photo) storage and sync service like Dropbox, Google Drive or iCloud Photos. Users upload files from one device and see them on all devices; they can share files and folders, keep versions, and work offline with…

Also reported as: Design Cross-Device Wallpaper Synchronization · Design ad click aggregator and file sync service

Design ad click aggregator and file sync service

Design an ad click and impression aggregation system. Ingest a high-volume stream of ad events ({ad_id, campaign_id, user_id, event_type, timestamp}, billions per day) and provide aggregated metrics (clicks, impressions, CTR per…

Also reported as: Design an Accurate Click Aggregator

Design a Distributed Token-Bucket Rate Limiter

Design a distributed rate limiter that protects APIs by limiting requests (or consumed units such as LLM billing tokens or storage quota) per user, API key, tenant, or IP. It must support configurable rules (e.g., 100…

Object-Oriented Design: Hotel Room Booking System

Design a hotel or rental booking system like Booking.com or Airbnb. Users search listings by location and date range with filters, view availability and a price quote, book a room or property, and cancel; hosts manage listings,…

Design a Centralized Logging System

Design a centralized logging platform (like ELK, Splunk or Datadog Logs) for a company with thousands of services and hosts. Agents collect logs from applications and infrastructure, ship them reliably under backpressure, and the…

Design APIs for a Voting System

Design the APIs and core data model for a voting system. First clarify the type of vote: identified or anonymous, single-choice or multi-choice, whether votes can be changed, and whether partial results are visible. Then define…

Design a smartwatch sensor subsystem

Design the sensing subsystem of a smartwatch: choose sensors (accelerometer, heart rate/PPG, GPS), decide sampling rates, process data on-device vs on the phone vs in the cloud, and balance accuracy against battery life. Discuss…

Design CI/CD for AI Services

Design a CI/CD platform like GitHub Actions or Jenkins. Source changes trigger pipelines of dependency-linked tasks (build, test, deploy) that run on a pool of workers with different capabilities. Users see live status and…

Design TikTok Data Engineering Systems

Design the data engineering systems behind a TikTok-scale short-video app: ingest user interaction events (views, likes, shares, watch time) at massive scale, process them in streaming and batch pipelines, and produce data for…

Design Apple News without ML

Design a news aggregation service like Google News. The system periodically pulls articles from thousands of publishers (RSS/APIs), stores article metadata (URL, title, publisher, topic ID, publish time), groups reports of the…

Design a multimodal RAG assistant

Design a retrieval-augmented generation (RAG) assistant that answers employee questions from an internal knowledge base containing text documents, images, PDFs and tables. Users ask natural-language questions and receive grounded…

Design Disk-Based Inventory Serving

Design software for a machine with no SSD and only a small amount of RAM that must serve inventory lookups and updates keyed by item ID from spinning disks. Minimize seeks: discuss the on-disk layout (B+ tree or hash index with…