Design a Durable Cron Job Scheduler
CursorSoftware Engineer · Technical Screen
Last updated
Design a cron scheduler with durable occurrences, timezone rules, missed-run policies, worker leases, idempotent dispatch, and failure recovery.
Design a durable cron job scheduler that runs recurring jobs according to a schedule. Explain schedule interpretation, dispatch, worker execution, recovery after failures, and behavior when a scheduled run is missed.
Constraints & Assumptions
- The source names the system without scale or delivery guarantees. State a baseline and distinguish execution attempts from logical scheduled occurrences.
- Each schedule has an explicit timezone. Clarify daylight-saving transitions and edits before defining next-run behavior.
- Do not promise exactly-once external side effects merely because a job record is unique.
Clarifying Questions to Ask
- Should missed runs be skipped, coalesced, or replayed individually?
- Can two occurrences of the same job overlap?
- Are job actions idempotent, and how should retries and permanent failures be surfaced?
- What happens to already-created occurrences when a schedule is edited or disabled?
Hints
Hint 1
Give one occurrence a stable identity: A scheduler restart can rediscover the same due time. A durable uniqueness rule should distinguish that logical run from a new execution attempt.
Follow-up questions
- What happens if a worker finishes the external action and crashes before recording success?
- How would the system recover after an hour-long scheduler outage without overwhelming workers?
Solution walkthrough is for members
Get the full walkthrough with reference code and complexity analysis, plus Kitty Coach at 300 messages a day. Hints, the code runner and community answers stay free.