11 curated sequences: each path connects systems that teach the same patterns. Free systems first where we can; Pro steps are marked.
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All five free systems in one path: warm-up shortener and IDs, then feed, chat, and messaging. No paywall mid-path.
All five free systems in one path: warm-up shortener and IDs, then feed, chat, and messaging. No paywall mid-path.
How read-dominated systems use caches, CDNs, consistent hashing, and precomputation to make the hot path effectively free.
The five systems that appear most in senior engineering loops, from a warm-up URL shortener to a full fan-out social feed and a payment system that cannot double-charge.
Queues, fan-out, retries, webhooks: when and why to decouple work from the request path.
Persistent connections, presence, pub/sub fanout, geo-indexed dispatch: designs where seconds matter.
From a leaderless KV store to an object store to a global event log: how data is stored, replicated, and retrieved at scale across fundamentally different storage engines.
How users find things: from the instant suggestions in a search box to the inverted index behind full-text search, location-based ranking, and the crawler that feeds it all.
Systems where failure is not an option: rate limits that fail open deliberately, schedulers that never drop a job, payment flows that cannot charge twice, and a wallet that never loses money mid-transfer.
The systems underneath the systems: unique ID generation, distributed object storage, event streaming, and a federated social protocol, the plumbing the internet runs on.
The architectures behind Netflix, TikTok, Airbnb, and the stock exchange, each one a masterclass in a different hard problem at scale.
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Open one free live system, or follow the month-by-month roadmap. You can go deeper on Pro later.