Job Scheduler
Enqueue instantly, execute reliably — even when every cron fires at once.
Keep enqueueing and executing jobs while a midnight cron thundering herd triples volume and a worker dies.
Enqueue and execute are different problems — accepting a job must never wait on running it. A queue decouples the two, and a worker fleet drains it; a job-status cache sits in front of the jobs store so completions and polls both survive a store blip.
Components in play
- Scheduler API — Accepts job submissions and enqueues them fast.
- Job queue — Absorbs the enqueue firehose ahead of execution.
- Job workers — Pulls jobs off the queue and executes them.
- Job-status cache — Holds hot completion/status records so the store stays idle.
- Jobs store — Durable job records, schedules and results.
Graded on these SLOs
- ≥ 96.00%Jobs enqueued & executed
- ≤ 260 msEnqueue-to-run p99
- ≥ 6.0k rpsSustain enqueue volume
- ≤ 88%Worker headroom
- ≤ 9Lean footprint
The brief
Design a background-job platform like a hosted Sidekiq or Temporal. Customers enqueue jobs through an API; a worker fleet executes them, sometimes on a schedule. Every customer's midnight cron jobs can fire in the same second — enqueuing has to stay fast through that thundering herd, and no job can silently vanish.
Functional
- Enqueue a job via an API and return fast
- Execute jobs on a worker fleet — on demand or on a schedule
- Report job status and results
Non-functional
- Enqueue must stay fast even during a scheduled thundering herd
- Execution can queue briefly under load, but a job must never be lost
- Status polling must not become a bottleneck on the jobs store
Warm-up: design decisions
Optional theory to prime the calls a senior engineer would make before you build.
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