Scalability

A product manager says PAY-204: next Friday's campaign may double checkout traffic for three hours. The beginner mistake is asking, "How many servers do we need…

A multi-tenant analytics platform partitions incoming events by tenant_id, hashed onto 16 shards — a design that looked perfectly balanced in every load test. T…

A URL shortener's redirect endpoint, GET /r/{code}, looks purely read-heavy — billions of redirects against a handful of short codes created per second. But eve…

A 4-node session cache scales to 5 nodes to handle more traffic. With hash(key) % N, that single node addition changes almost every key's target node, and the c…

A shopping cart must remember items, so the product cannot be literally stateless. The useful design question is where that state lives. Keep the cart inside on…

A load balancer spreads connections so one machine does not take all the pain. Layer 4 routes on IP and port — fast and protocol-agnostic. Layer 7 reads HTTP ho…