·13 min read
Your cron ran twice: why exactly-once scheduling does not exist
A job runs at midnight for four years, then runs twice with no deploy. The prime suspect is a daylight-saving fall-back, but there are eight others — clock steps, duplicate schedulers, catch-up controllers, lost acks. How to tell them apart from the logs in ten minutes, and why the real fix is a run key with a unique index rather than a better schedule.
Intermediate- Scheduling
- Reliability
- Distributed Systems
- Operations
