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🏗 Interview Prep

System Design

Scaling, caching, databases, queues and the classic "design X" questions, each with a diagram you can step through.

📘 Learn it from scratch

Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.

Scaling from 1 to 1 Million UsersCaching Strategies & Building an LRU CacheLoad BalancersDatabases at Scale: Replication & ShardingQueues & Background JobsAcing System Design Interviews (+ Rate Limiter)

100 questions, most asked first

Ordered so the most useful questions for learning each pattern come first.

Any difficulty Easy Medium Hard

All patterns Design interview Scaling basics Caching Load balancing Databases at scale Consistent hashing CAP & consistency Queues & async Rate limiting CDNs & storage Real-time Reliability

#5Scaling the databaseDatabases at scaleHardFree #6Consistent hashingConsistent hashingHardFree Unlock 46 more System Design questions · all 1,200 questions for $39/year (about 11¢ a day)See full access #11Design a chat app (like WhatsApp)Real-timeHard🔒#12Design a news feed (like Twitter or Instagram)Design interviewHard🔒#14Design search autocomplete (backend)Design interviewHard🔒#15Design a web crawlerDesign interviewHard🔒#16Design a distributed cache (like Redis Cluster)CachingHard🔒#17Design a photo-sharing app (like Instagram)Design interviewHard🔒#18Design a video platform (like YouTube)CDNs & storageHard🔒#19Design a ride-sharing app (like Uber)Real-timeHard🔒#20Design a ticket booking system (like Ticketmaster)CAP & consistencyHard🔒#22Design a distributed key-value storeCAP & consistencyHard🔒#23Design a payment systemDesign interviewHard🔒#25Design file sync (like Google Drive or Dropbox)CDNs & storageHard🔒#26Design a metrics and alerting systemReliabilityHard🔒#28Design an online code judge (like LeetCode)Queues & asyncHard🔒#36Distributed transactions and the saga patternQueues & asyncHard🔒#38Sharding strategiesDatabases at scaleHard🔒#39Bloom filtersCachingHard🔒#40Leader election and consensus (Raft)CAP & consistencyHard🔒#44Going multi-regionCAP & consistencyHard🔒#45Backpressure and load sheddingReliabilityHard🔒#46Scaling WebSockets to millions of connectionsReal-timeHard🔒#47The transactional outbox patternQueues & asyncHard🔒#48CQRS and event sourcingDatabases at scaleHard🔒#49Hot keys and the thundering herdCachingHard🔒#51Design a collaborative editor (like Google Docs)Real-timeHard🔒#53Design a distributed job scheduler (cron at scale)Queues & asyncHard🔒#55Design an ad-click counter at massive scaleQueues & asyncHard🔒#56Design an e-commerce cart and checkoutCAP & consistencyHard🔒#57Design live comments for a stream (like Twitch chat)Real-timeHard🔒#58Design a recommendation systemDesign interviewHard🔒#65Strong, eventual and read-your-writes consistencyCAP & consistencyHard🔒#66B-tree vs LSM-tree storage enginesDatabases at scaleHard🔒#67At-most-once, at-least-once, exactly-onceQueues & asyncHard🔒#72Design price alerts (stocks or flights)Queues & asyncHard🔒#73Design an email service (like Gmail)Databases at scaleHard🔒#75Design a distributed message queue (like Kafka)Queues & asyncHard🔒#78Design video calling (like Zoom)Real-timeHard🔒#79Design maps and turn-by-turn routing (like Google Maps)Design interviewHard🔒#84Distributed locksCAP & consistencyHard🔒#85Time, clocks and ordering eventsCAP & consistencyHard🔒#87Heartbeats, failure detection and gossipReliabilityHard🔒#88Cache invalidation strategiesCachingHard🔒#91Design trending topics (top-K heavy hitters)Queues & asyncHard🔒#92How does object storage (like S3) work?CDNs & storageHard🔒#95Design a banking ledgerCAP & consistencyHard🔒#96Design a food delivery appReal-timeHard🔒