Real-time & Messaging
Pushing data the moment it changes — WebSockets, fan-out, streaming and message queues — across chat, feeds, notifications and collaborative editing.
System Designs 11
Design Uber
Build a planet-scale ride-hailing system step by step. Learn how to handle real-time location tracking, matching algorithms, scalability, and payments through an interactive diagram that grows with each concept.
Design WhatsApp
Build a real-time messaging system step by step. See how persistent WebSockets, a session registry, offline inbox queues, the ✓✓ delivery receipts, group fan-out, media on a CDN, and end-to-end encryption fit together — through an animated, live chat-driven diagram that grows with each concept.
Design Twitter
Build Twitter's news feed step by step. Learn the social graph, why fan-out on write beats read-time merging, how a precomputed timeline cache makes feed reads O(1), how ranking surfaces the best tweets, and how a hybrid model solves the celebrity problem — through an interactive diagram that grows with each concept.
Design a Notification System
Build a multi-channel notification system step by step. See how one API, a message queue and a worker fleet decouple slow third-party delivery, how preferences and quiet hours gate every send, how templates fan out to push, SMS and email, and how delivery tracking, retries, dedup and rate limits keep it reliable — through an interactive diagram that grows with each concept.
Design a Message Queue
Build a distributed message queue like Kafka step by step. See how an append-only commit log, partitions keyed for order, consumer groups with server-side offsets, leader/follower replication, controller-driven leader election, retention and compaction, and exactly-once guarantees fit together — through an interactive diagram that grows with each concept.
Design a News Feed
Build a social news feed step by step. See how the social graph, pull vs push fan-out, a precomputed feed cache, relevance ranking, the hybrid model that tames the celebrity problem, blending multiple content sources, and cursor pagination fit together — through an interactive diagram that grows with each concept.
Design Google Docs
Build a real-time collaborative editor step by step. See how edits become tiny operations, how OT and CRDTs resolve concurrent edits so every copy converges, how ops broadcast over WebSockets, how an op log plus snapshots give history and recovery, and how presence, offline sync and per-document sharding fit together — through an interactive diagram that grows with each concept.
Design Netflix
Build a planet-scale video streaming service step by step. See how the play path splits authorization from byte delivery, how origin storage and CDN edges serve immutable segments, how an adaptive-bitrate ladder adapts to any connection, how a parallel transcoding pipeline builds it, and how Open Connect, recommendations and QoE events fit together — through an interactive diagram that grows with each concept.
Design Instagram
Build a photo-sharing app step by step. See how splitting media from metadata, a CDN for immutable images, async image processing, a precomputed feed cache, asynchronous like/view counters, TTL-based ephemeral stories, and sharding fit together to serve billions of photos — through an interactive diagram that grows with each concept.
Design an Ad Click Aggregator
Build a real-time ad click aggregator step by step. See how a thin ingest API and event stream absorb millions of clicks a second, how a stream processor aggregates into time windows, how dedup keys give exactly-once counts, how a raw event lake and batch recompute reconcile the numbers, and how fraud filtering and watermarks handle the sharp edges — through an interactive diagram that grows with each concept.
Design Slack
Build a team chat app step by step. See how channel messaging and per-channel history, real-time delivery over WebSockets with a session registry, cross-server fan-out via pub/sub, ephemeral presence and typing, message search, unread counts and notifications, and channel sharding fit together — through an interactive diagram that grows with each concept.