Apple System Design Questions

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 worded as: Design Cross-Device Wallpaper Synchronization · 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 worded as: Design an Accurate Click Aggregator

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…

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 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 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 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 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 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 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 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…