System designHardsd-g640

Subject Distributed scheduler lockingLevel Senior–Staff~45 minCommon in Concurrency · Distributed systems interviewsIndustries Technology, Software development

Question

Design a scheduler that runs periodic jobs (cron-like, e.g. "send the 9am digest", "reconcile billing hourly") across a fleet of N identical scheduler nodes for high availability, where each scheduled trigger must fire on exactly one node — double-execution sends duplicate emails or double-charges. Constraints: any node can die, the schedule must keep firing, and a network partition must not cause two nodes to both fire the same tick. Describe how a tick is claimed, how concurrent nodes coordinate, and the duplicate-firing safeguards.

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.