Build a Shadow Traffic / Dark Launch System Premium
Design a traffic mirroring system that duplicates live production requests to a canary service in real-time, compares responses for divergence, and generates a confidence report without any user-visible impact.
Build Slack's Channel Message Fan-Out and Unread Counts Premium
Design a messaging system that delivers channel messages to thousands of members in a large workspace, maintains accurate unread counts per user per channel, and syncs read state across multiple devices.
Build a Social Graph Service at 500M Users Free
Design a graph service that answers 'does user A follow user B?' in under 1ms, supports mutual friend queries, and stays consistent as billions of follow/unfollow events happen every day.
Build Spotify's Song Radio Feature Premium
Design a real-time playlist generator that uses a seed song to produce an infinite radio stream of acoustically and contextually similar tracks, personalizes the mix per listener, and avoids repetition across sessions.
Build a Time-Series Metrics Store Premium
Design a metrics storage engine that compresses billions of data points efficiently, supports fast range queries for dashboard rendering, and retains high-resolution data for 15 days before downsampling.
Build Twitter's At-Mention Fan-Out for Celebrities Premium
Design a fan-out system that notifies the followers of a celebrity with 100 million followers when they are mentioned, without triggering a write storm that takes down the database.
Build Twitter's Trending Topics Pipeline Premium
Design a system that detects emerging viral signals from a stream of 500,000 tweets per second, computes trending topics per region, and refreshes trends every 60 seconds without reprocessing the full history.
Build Uber's Real-Time Driver-Rider Matching System Free
Design a matching system that pairs riders with the nearest available driver in dense urban areas within 2 seconds, handles thousands of concurrent match requests, and degrades gracefully during demand spikes.
Build Uber's Surge Pricing Engine Free
Design a dynamic pricing system that detects supply-demand imbalance in each geographic zone, computes surge multipliers in under a second, and communicates price changes to riders and drivers without race conditions.
Build TinyURL - A URL Shortener at Scale Premium
Design a URL shortening service that generates collision-free short codes, handles 100,000 redirects per second with sub-10ms latency, and tracks click analytics without slowing down redirects.