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cron.surf

Run a Kubernetes CronJob every 5 seconds

Kubernetes has no exact expression for “Every 5 seconds”. Here is why, a workaround, and the platforms that can do it. A Kubernetes CronJob reads five-field cron in spec.schedule and starts a Job for each run.

Why Kubernetes can’t do this exactly

Defined on Quartz as */5 * * * * ? · “Every 5 seconds”

  • second: Kubernetes has no seconds field, so it cannot run at seconds other than 0.

    WorkaroundRun every minute and repeat inside the job with sleep, or use a scheduler that has seconds (Spring, Quartz, a systemd timer).

Kubernetes gotchas

Day of week is 0-6The schedule parser stops at 6. Write 0 for Sunday; 7 is an error.
Too many missed startsIf a CronJob misses more than 100 starts, the controller stops starting it. Set startingDeadlineSeconds so old misses stop counting.
Overlapping runsconcurrencyPolicy defaults to Allow, so a slow Job can overlap the next one. Use Forbid or Replace.
*/n in a day field counts as setOnly * or ? leave a day field open. 0 0 */2 * 1 runs on odd days or on Mondays, while Vixie cron reads it as odd days that are Mondays.

FAQ

What is the Kubernetes cron expression for “Every 5 seconds”?

There is none that matches exactly. Kubernetes has no seconds field, so it cannot run at seconds other than 0.

Which time zone does a Kubernetes schedule use?

Without spec.timeZone, in the local zone of kube-controller-manager, which is usually UTC. Set spec.timeZone (stable since Kubernetes 1.27) to an IANA name. CRON_TZ or TZ inside schedule is rejected.

Does a CronJob support @daily?

Yes. @yearly, @monthly, @weekly, @daily and @hourly work in spec.schedule.

Why did my CronJob run twice, or not at all?

A CronJob creates about one Job per scheduled time, not exactly one. Make the Job safe to repeat, and check startingDeadlineSeconds and concurrencyPolicy.