Run a Kubernetes CronJob every 3 hours

The Kubernetes expression for “Every 3 hours” is 0 */3 * * *. Below: config you can paste, the next run times, and what to watch out for. A Kubernetes CronJob reads five-field cron in spec.schedule and starts a Job for each run.

0 */3 * * *Open in tool

“On the hour, every 3 hours”

CronJob manifest

every-3-hours.yaml

apiVersion: batch/v1
kind: CronJob
metadata:
  name: every-3-hours
spec:
  schedule: "0 */3 * * *"
  timeZone: "Etc/UTC"
  concurrencyPolicy: Forbid
  startingDeadlineSeconds: 300
  jobTemplate:
    spec:
      template:
        spec:
          restartPolicy: OnFailure
          containers:
            - name: job
              image: busybox:1.37
              command: ["sh", "-c", "echo running every-3-hours"]

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 3 hours”?

0 */3 * * *. It reads: On the hour, every 3 hours

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.