[SOLVED] Schedule a Kubernetes cronjob to run just once

Issue

How can I schedule a Kubernetes cron job to run at a specific time and just once?

(Or alternatively, a Kubernetes job which is not scheduled to run right away, but delayed for some amount of time – what is in some scheduling systems referred to as "earliest time to run".)

The documentation says:

Cron jobs can also schedule individual tasks for a specific time [...]

But how does that work in terms of job history; is the control plane smart enough to know that the scheduling is for a specific time and won't be recurring?

Solution

You can always put specific minute, hour, day, month in the schedule cron expression, for example 12:15am on 25th of December:

apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "15 0 25 12 *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            imagePullPolicy: IfNotPresent
            command:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes cluster
          restartPolicy: OnFailure

Unfortunately it does not support specifying the year (the single * in the cron expression is for the day of the week) but you have one year to remove the cronjob before the same date & time comes again for the following year.

Answered By - Lukman