Systems Design

The capstone: put the HTTP, caching, database and messaging units together into designs you can defend. Start with a repeatable order of work — requirements, estimates with their arithmetic shown, API, data model, then scale — then the read and write paths a growing system needs (caches and how they go stale, replicas and their lag, shards and how keys move), and finish with the arguments a design review actually asks for: fan-out on write or read, which rate limiter, and what happens when every client retries at once.