Task scheduler

How this question breaks down

1. 1Delayed jobsCore25 minStore work that must run at a future instant, find it cheaply when it falls due, and hand it to workers within seconds of that instant.
2. 2CronCore21 minTurn hundreds of thousands of recurring schedules into exactly one run per scheduled instant, spread so they do not all start on the hour, correct across time zones and DST, with a clear rule for runs that were missed.
3. 3LeasesCore20 minA lease gives one worker a job for a limited time that it must keep renewing; paired with a fencing token and an idempotent effect, it turns at-least-once execution into a result that happens once.

Work through the parts in order and you’ve covered the full design. Each part is one topic.