Distributed Systems Theory interview questions

Time and ordering, leader election, quorums, idempotence, and classic impossibility results.

3 questions in Backend Engineering.

Backend EngineeringA 28-minute read on how the topic fits together, before the questions.Backend engineering fundamentals56 short answers on one page, for revising rather than studying.

hard3

hardConcept

One node stops answering. How does the rest of the cluster decide whether it has crashed or is merely slow, and what does that decision cost you?

You cannot distinguish a crashed process from a slow one, so every failure detector is a timeout and every timeout is a guess. Choose which error you can afford: declaring a live node dead risks two writers, waiting risks a stall, and only fencing makes the first survivable.

5 minsenior, staff, lead

hardScenarioDesign

Design a distributed lock manager for a high-frequency trading platform where microsecond latency is critical and stale locks can result in massive financial losses.

Designing an ultra-low latency distributed lock manager, evaluating consensus algorithms, and handling clock drift in high-frequency environments.

3 minsenior, staff

hardConcept

Two servers each write a record stamped with its own clock. Why can you not use those timestamps to decide which write happened first, and what do you use instead?

Wall clocks on separate machines disagree by an unbounded amount and can jump backwards, so their timestamps order events by accident rather than by causality. Logical and vector clocks capture what preceded what, quorums give overlap not order, and a lease is safe only with a fencing token.

7 minsenior, staff, lead