An API gateway is the single entry point for all client requests in a microservices architecture. It sits in front […]

Collaborative document editing allows multiple users to edit the same document simultaneously, with changes from all users appearing in real

A typeahead (autocomplete) service returns ranked completions for a query prefix in under 100ms. Google Search completes queries as you

An ad click tracking system records every click on an advertisement, deduplicates fraudulent clicks, aggregates counts for billing, and provides

A shopping cart stores a user’s intended purchases before checkout. The design must handle: anonymous users (no account), authenticated users

A distributed task queue decouples work from workers: producers enqueue tasks, workers consume and execute them asynchronously. This enables horizontal

A key-value store is the simplest form of a database: store a value associated with a key, retrieve the value

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

A ticketing system (like Ticketmaster for concerts, or an airline seat booking system) manages limited inventory under simultaneous high demand.

A recommendation system suggests relevant items to users — products to buy, videos to watch, friends to follow. At Netflix,

A payments system processes financial transactions — charge customers, transfer funds, process refunds. Unlike typical web applications, payments demand ACID

A social network feed aggregates posts from accounts a user follows, ranked by relevance or recency. At Instagram or Twitter

A video streaming platform (like Netflix or YouTube) must ingest raw video, encode it into multiple quality levels, distribute it