distributed systems

Every queue, webhook, and retry loop you'll ever deploy at a customer hides this distinction. Interviewers use it to separate people who've shipped from people who've read about shipping.

The bug only appears under load, the code 'hasn't changed,' and the customer just got charged twice. There's one root-cause pattern behind almost every version of this incident, and a fix with a subtle race most candidates miss.

CAP is a trap if you recite it. The interviewer wants to see you map a customer's real datastore to a real failure mode, then decide where stale reads are free and where they corrupt an agent's decision.

The source can only upload the file a handful of times before it saturates, but every receiver also has upload bandwidth. The win is making peers serve each other, so total capacity grows with the swarm instead of bottlenecking on one machine.