Most distributed systems at least promise they do something at least once or at most once. You can often achieve exactly once in practice with a combination of

Most distributed systems at least promise they do something at least once or at most once. You can often achieve exactly once in practice with a combination of idempotent APIs and a shared database. For a task runner, there are a lot of different behaviours you might want if the system crashes. Maybe the runner should “catch up” after coming back online. That’s easy enough to achieve if you move away from cron and track which tasks have been run in a small data store somewhere.