Distributed cron single-execution guarantee
Design a distributed cron/scheduler that runs ~5,000 recurring jobs (send daily digest emails, generate invoices, expire sessions) across a fleet of 30 worker nodes. Each scheduled job must run exactly once per scheduled tick — never zero times (missed) and never twice (duplicate invoice). Nodes can crash mid-run or be slow. How do you coordinate which node runs which job and guarantee single execution per tick?
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.