Each system below is a real architecture you can run, not just read. Hit play and watch a request flow through the components step by step; click any box to see why it's there and what you'd use instead; trigger a failure scenario to see what breaks and how the system recovers. Every system includes back-of-envelope capacity math and a recap quiz. Start with a Beginner system like the URL Shortener, then work up to Advanced ones like Kafka or the Stock Exchange matching engine.
Hashing, key generation, read-heavy caching.
Fan-out on write vs read, ranking, CDN.
Persistent connections, message queues, delivery.
Room-based pub/sub fanout across gateway instances.
Geo-indexing, dispatch, real-time location streams.
CDN-first, adaptive bitrate, recommendation.
Idempotency, fraud, async webhooks, ledger.
Chunking, content-addressed dedup, multi-device sync.
Multi-channel async delivery, user preferences, retries.
Video pipeline, ML-driven recommendation, infinite scroll.
Web crawl, inverted index, scatter-gather query, ranking.
Geohashing, nearby search, review writes, hot-query caching.
Seat holds, payment timeouts, virtual queue for hot events.
Hybrid fan-out: push for most users, pull for celebrities, merged at read.
Partitioned, replicated log. Brokers, ISR, consumer groups, leader failover.
Multi-AZ erasure coding, sharded metadata, strong read-after-write.
Operational Transforms, per-document op log, snapshot + delta replay.
Single-threaded per-symbol matching, in-memory order book, microsecond latency.
Geo-search, atomic seat-holds, authorize-then-capture payments, async fan-out.
Federated social: per-user PDS, global firehose Relay, plug-in AppViews and custom feeds.