2. Design a Distributed Rate Limiter
Enforce tenant quotas across servers while making burst behavior and outage policy explicit.
ClassicMedium
Guided practice
Start with a template. Work through each step. Ask Coach when you need a second opinion.
Classic designs 15
Ordered by design numberCompany tags are community-reported. Counts on cards show how many people reported that design.
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3. Design a Distributed Cache
Partition cached data, survive node loss and keep cache misses from overwhelming the source of truth.
ClassicMedium6. Design a News Feed
Build a paginated feed that handles high-fan-out authors, fresh posts and visibility changes.
ClassicMedium43. Design YouTube Top-K
The K most-viewed videos for the last hour, day, month and all time from 700,000 views a second, exactly and in milliseconds.
ClassicMedium47. Design an Online Judge like LeetCode
Run strangers' code safely in single-use microVMs, return verdicts within 5 seconds, and rank 100,000 contestants live.
ClassicMedium50. Design a Ride-Sharing Service like Uber
Price a trip, match a rider to a nearby driver who has ten seconds to accept, and never give one driver two rides.
ClassicMedium54. Design a Photo Sharing App like Instagram
Photos and videos for 500 million daily users: presigned multipart uploads, a processing pipeline, CloudFront and a hybrid fan-out feed.
ClassicMedium57. Design Post Search like Facebook
Search a billion posts a day by keyword, newest or most liked first, with an inverted index you build yourself.
ClassicMedium58. Design a Dating App like Tinder
Stacks of nearby people in under 300 ms, 2 billion swipes a day, and a match never missed even when both like at once.
ClassicMedium59. Design a Fitness Tracking App like Strava
Record runs and rides on the phone without signal, upload each once, show them to friends and rank athletes by week, month and year.
ClassicMedium62. Design a Flash Sale System
Sell 10,000 units to a million people at noon with a lottery waiting room, a Redis gate before an Aurora ledger and holds that expire.
ClassicMedium66. Design for Read Scale: A Product Page Read a Million Times a Second
Serve a product page a million times a second: a cheap query, replicas, Redis and the edge, with hot keys, stampedes and invalidation handled.
ClassicMedium70. Design an In-Memory Data Store like Redis
An in-memory data store like Redis, from one event loop to Redis Cluster to a durable platform.
ClassicMedium81. Design a Proximity Search Service
Radius, k-nearest and map-box search over places that rarely move and drivers that ping every few seconds: R-trees, geohash, H3 and S2 cells, Redis GEO and OpenSearch. One-hour boards for junior, senior and staff, with the theory.
ClassicMedium93. Design a Real-Time Game Leaderboard
Rank 200 million players in real time with sharded Redis sorted sets, count every game exactly once, and close a season fairly.
ClassicMedium