End-to-end system design for a Twitter / News Feed service. Functional + non-functional requirements, capacity, schema, fanout-on-write vs fanout-on-read, hybrid for celebrities, ranking, caching, and what interviewers love.
How to design a distributed rate limiter end-to-end. The four classic algorithms, when to pick each, a Redis Lua implementation, distributed coordination, and the gotchas (clock skew, hot keys, fairness).
End-to-end system design for a URL shortener — requirements, capacity estimation, ID generation (counter, hash, base62), schema, caching, analytics, abuse prevention, and the parts most write-ups skip.
A backend engineer’s working mental model for distributed systems. Failure modes, CAP, replication, partitioning, consistency, time and ordering, idempotency — explained without the textbook.