🏗 Interview Prep
System Design
Scaling, caching, databases, queues and the classic "design X" questions, each with a diagram you can step through.
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Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.
100 questions, most asked first
Ranked by how often each question comes up in real interviews. #1 is the most common.
All patternsDesign interviewScaling basicsCachingLoad balancingDatabases at scaleConsistent hashingCAP & consistencyQueues & asyncRate limitingCDNs & storageReal-timeReliability
#1🏗Design a URL shortener (like bit.ly)Design interviewMediumFree#2🏗How do you scale a web app from 1 to 1 million users?Scaling basicsMediumFree#3🏗Caching strategiesCachingMediumFree#4🏗Load balancersLoad balancingMediumFree#5🏗Scaling the databaseDatabases at scaleHardFree#6🏗Consistent hashingConsistent hashingHardFree#7🏗The CAP theoremCAP & consistencyMediumFree#8🏗Message queues and background jobsQueues & asyncMediumFree#9🏗Design a rate limiterRate limitingMediumFree#10🏗Serving images and video at scaleCDNs & storageMediumFree🔓Unlock 90 more System Design questions · all 1,200 questions for $39/year (about 11¢ a day)See full access#11🏗Design a chat app (like WhatsApp)Real-timeHard🔒#12🏗Design a news feed (like Twitter or Instagram)Design interviewHard🔒#13🏗Design a notification systemQueues & asyncMedium🔒#14🏗Design search autocomplete (backend)Design interviewHard🔒#15🏗Design a web crawlerDesign interviewHard🔒#16🏗Design a distributed cache (like Redis Cluster)CachingHard🔒#17🏗Design a photo-sharing app (like Instagram)Design interviewHard🔒#18🏗Design a video platform (like YouTube)CDNs & storageHard🔒#19🏗Design a ride-sharing app (like Uber)Real-timeHard🔒#20🏗Design a ticket booking system (like Ticketmaster)CAP & consistencyHard🔒#21🏗Design a unique ID generatorDesign interviewMedium🔒#22🏗Design a distributed key-value storeCAP & consistencyHard🔒#23🏗Design a payment systemDesign interviewHard🔒#24🏗Design a real-time leaderboardCachingMedium🔒#25🏗Design file sync (like Google Drive or Dropbox)CDNs & storageHard🔒#26🏗Design a metrics and alerting systemReliabilityHard🔒#27🏗What does an API gateway do?Load balancingMedium🔒#28🏗Design an online code judge (like LeetCode)Queues & asyncHard🔒#29🏗Design a pastebinDesign interviewEasy🔒#30🏗Add full-text search to a websiteDatabases at scaleMedium🔒#31🏗Monolith vs microservicesScaling basicsMedium🔒#32🏗Back-of-the-envelope estimationDesign interviewMedium🔒#33🏗Latency numbers every engineer should knowScaling basicsMedium🔒#34🏗Availability, SLAs and the "nines"ReliabilityMedium🔒#35🏗Circuit breakers, timeouts and retriesReliabilityMedium🔒#36🏗Distributed transactions and the saga patternQueues & asyncHard🔒#37🏗Event-driven architecture and pub/subQueues & asyncMedium🔒#38🏗Sharding strategiesDatabases at scaleHard🔒#39🏗Bloom filtersCachingHard🔒#40🏗Leader election and consensus (Raft)CAP & consistencyHard🔒#41🏗Blue-green, canary and rolling deploymentsReliabilityMedium🔒#42🏗Logs, metrics and traces (observability)ReliabilityMedium🔒#43🏗Backups and disaster recovery (RPO and RTO)ReliabilityMedium🔒#44🏗Going multi-regionCAP & consistencyHard🔒#45🏗Backpressure and load sheddingReliabilityHard🔒#46🏗Scaling WebSockets to millions of connectionsReal-timeHard🔒#47🏗The transactional outbox patternQueues & asyncHard🔒#48🏗CQRS and event sourcingDatabases at scaleHard🔒#49🏗Hot keys and the thundering herdCachingHard🔒#50🏗Edge computing and serverlessCDNs & storageMedium🔒#51🏗Design a collaborative editor (like Google Docs)Real-timeHard🔒#52🏗Design "restaurants near me" (like Yelp)Databases at scaleMedium🔒#53🏗Design a distributed job scheduler (cron at scale)Queues & asyncHard🔒#54🏗Design reliable webhook deliveryQueues & asyncMedium🔒#55🏗Design an ad-click counter at massive scaleQueues & asyncHard🔒#56🏗Design an e-commerce cart and checkoutCAP & consistencyHard🔒#57🏗Design live comments for a stream (like Twitch chat)Real-timeHard🔒#58🏗Design a recommendation systemDesign interviewHard🔒#59🏗Design centralized loggingReliabilityMedium🔒#60🏗Design an online learning platform (like this one)Design interviewMedium🔒#61🏗Forward proxy vs reverse proxyLoad balancingEasy🔒#62🏗Stateless vs stateful servicesScaling basicsMedium🔒#63🏗Sticky sessionsLoad balancingMedium🔒#64🏗Block vs file vs object storageCDNs & storageMedium🔒#65🏗Strong, eventual and read-your-writes consistencyCAP & consistencyHard🔒#66🏗B-tree vs LSM-tree storage enginesDatabases at scaleHard🔒#67🏗At-most-once, at-least-once, exactly-onceQueues & asyncHard🔒#68🏗Cache eviction policiesCachingMedium🔒#69🏗Security in system design interviewsReliabilityMedium🔒#70🏗Data pipelines, warehouses and lakesDatabases at scaleMedium🔒#71🏗Design view and like countersCachingMedium🔒#72🏗Design price alerts (stocks or flights)Queues & asyncHard🔒#73🏗Design an email service (like Gmail)Databases at scaleHard🔒#74🏗Design a calendar with schedulingDesign interviewMedium🔒#75🏗Design a distributed message queue (like Kafka)Queues & asyncHard🔒#76🏗Design a feature flag systemReliabilityMedium🔒#77🏗Design a content moderation pipelineQueues & asyncMedium🔒#78🏗Design video calling (like Zoom)Real-timeHard🔒#79🏗Design maps and turn-by-turn routing (like Google Maps)Design interviewHard🔒#80🏗Design a live poll or voting systemCAP & consistencyMedium🔒#81🏗How to run a system design interviewDesign interviewMedium🔒#82🏗Non-functional requirementsDesign interviewEasy🔒#83🏗How to choose a database for a designDatabases at scaleMedium🔒#84🏗Distributed locksCAP & consistencyHard🔒#85🏗Time, clocks and ordering eventsCAP & consistencyHard🔒#86🏗Service discoveryLoad balancingMedium🔒#87🏗Heartbeats, failure detection and gossipReliabilityHard🔒#88🏗Cache invalidation strategiesCachingHard🔒#89🏗API versioning and backward compatibilityDesign interviewMedium🔒#90🏗Graceful degradationReliabilityMedium🔒#91🏗Design trending topics (top-K heavy hitters)Queues & asyncHard🔒#92🏗How does object storage (like S3) work?CDNs & storageHard🔒#93🏗AutoscalingScaling basicsMedium🔒#94🏗Containers and Kubernetes in system designScaling basicsMedium🔒#95🏗Design a banking ledgerCAP & consistencyHard🔒#96🏗Design a food delivery appReal-timeHard🔒#97🏗Design a hotel booking systemCAP & consistencyMedium🔒#98🏗Designing for privacy (GDPR) and data deletionReliabilityMedium🔒#99🏗Designing for costScaling basicsMedium🔒#100🏗Walk me through the design of something you builtDesign interviewMedium🔒