System Design

⏱ 6 min read A shopping cart stores a user’s intended purchases before checkout. The design must handle: anonymous users (no account), authenticated users […] Read article

⏱ 6 min read An ad click tracking system records every click on an advertisement, deduplicates fraudulent clicks, aggregates counts for billing, and provides Read article

⏱ 6 min read A ticketing system (like Ticketmaster for concerts, or an airline seat booking system) manages limited inventory under simultaneous high demand. Read article

⏱ 6 min read A ride-sharing platform (Uber, Lyft) matches riders with nearby drivers in real time, handles surge pricing, tracks vehicle positions, and Read article

⏱ 6 min read A key-value store is the simplest form of a database: store a value associated with a key, retrieve the value Read article

⏱ 6 min read A social network feed aggregates posts from accounts a user follows, ranked by relevance or recency. At Instagram or Twitter Read article

⏱ 6 min read A payments system processes financial transactions — charge customers, transfer funds, process refunds. Unlike typical web applications, payments demand ACID Read article

⏱ 6 min read A recommendation system suggests relevant items to users — products to buy, videos to watch, friends to follow. At Netflix, Read article

⏱ 6 min read A file storage system (like Dropbox or Google Drive) stores user files, provides sync across devices, and handles concurrent edits. Read article

⏱ 6 min read A search autocomplete system provides real-time suggestions as users type, ranking completions by popularity or relevance. At Google or Amazon Read article

⏱ 6 min read A video streaming platform (like Netflix or YouTube) must ingest raw video, encode it into multiple quality levels, distribute it Read article

⏱ 6 min read A URL shortener converts a long URL into a short alias (e.g., bit.ly/abc123) that redirects to the original. Building one Read article

⏱ 6 min read A notification system delivers messages to users through one or more channels — push notifications, email, SMS, in-app. At scale Read article

⏱ 6 min read The gossip protocol (epidemic protocol) is a peer-to-peer communication method where each node periodically shares information with a small number Read article

⏱ 6 min read Real-time server-to-client communication requires the server to push data without waiting for a client request. Three primary patterns exist: long Read article