Advanced System Design

The distributed-systems interview set — a hash ring that barely moves, a filter that says maybe, a window that slides, a breaker that opens.

Place cache nodes on a hash ring so that adding or removing one barely remaps the keys — the placement rule behind every distributed cache.

Build the probabilistic membership filter — never a false negative, rarely a false positive, and never the item itself.

Count requests inside a moving window of wall time — old acquisitions fall out at exactly the boundary, new ones queue nothing.

Stop hammering a failing dependency — closed, open, half-open, with an injected clock deciding when one careful probe may run again.