CronJob

Imagine a virtual timekeeper, ticking along to the Linux system's crontab, triggering particular tasks to run at the precise time designated. This is the idea behind 'CronJob'.

API Version Cheat Sheet

Kubernetes Version	Batch API Version	Activated By Default?
v1.5-v1.7	batch/v2alpha1	No
v1.8-v1.20	batch/v1beta1	Yes
v1.21+	batch/v1	Yes

A word of caution: when executing APIs that aren't activated by default, users must configure --runtime-config=batch/v2alpha1 in the kube-apiserver.

CronJob Specs

• .spec.schedule outlines the schedule of task execution, akin to the Cron format.

• .spec.jobTemplate lists the tasks that need running, and mirrors the Job format.

• .spec.startingDeadlineSeconds specifies the deadline for initiating tasks.

• .spec.concurrencyPolicy delineates the policy for task concurrency, providing three options: Allow, Forbid, and Replace.

apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            imagePullPolicy: IfNotPresent
            command:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes cluster
          restartPolicy: OnFailure

$ kubectl create -f cronjob.yaml
cronjob "hello" created

You can also use kubectl run to create a CronJob:

kubectl run hello --schedule="*/1 * * * *" --restart=OnFailure --image=busybox -- /bin/sh -c "date; echo Hello from the Kubernetes cluster"

$ kubectl get cronjob
NAME      SCHEDULE      SUSPEND   ACTIVE    LAST-SCHEDULE
hello     */1 * * * *   False     0         <none>
$ kubectl get jobs
NAME               DESIRED   SUCCESSFUL   AGE
hello-1202039034   1         1            49s
$ pods=$(kubectl get pods --selector=job-name=hello-1202039034 --output=jsonpath={.items..metadata.name} -a)
$ kubectl logs $pods
Mon Aug 29 21:34:09 UTC 2016
Hello from the Kubernetes cluster

# When deleting a cronjob, it will also delete its created jobs and pods and stop the creation of new jobs.
$ kubectl delete cronjob hello
cronjob "hello" deleted

Additional Resources

• Cron Jobs