Jobs & Cronjobs

A Job is a Kubernetes object that executes a workload and then terminates once the workload is complete. When a Job finishes, the containers involved are terminated and the Pod transitions to the Completed state.

Jobs and Pods are similar in that they’re both used to run containers. However, Pods typically run containers continuously, whereas Jobs run containers to do a discrete piece of work and then terminate.

The sample Job below is taken from the Kubernetes documentation and uses Perl to compute π to 2000 decimal places.

apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  template:
    spec:
      containers:
        - name: pi
          image: perl
          command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: Never
  backoffLimit: 4

When we create this Job, the container runs for 9 seconds and then terminates.

We can see the script output by viewing the Pod logs for this Job .

CronJobs

A

CronJob is a Kubernetes object that executes a workload on a schedule. A CronJob is an extension of a Job but rather than running once and terminating, a CronJob runs according to a schedule specified in the manifest. The following CronJob definition runs a container that prints the current date/time and the text CronJob running!!. The schedule attribute specifies how often the workload should run. In this case,  */1 * * * * tells Kubernetes to run the workload very minute.

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: cronjob-sample
spec:
  schedule: "*/1 * * * *" #run every minute
  jobTemplate:
    spec: # Job Spec
      template: # Pod Template
        spec: # Pod Spec
          containers:
            - name: cron-container
              image: busybox
              command: ['sh', '-c', 'date; echo CronJob running!!']
          restartPolicy: OnFailure

After creating the definition above we can list the

CronJob and the Pods that it has created. As you can see from the screenshot, a new Pod is created every minute.

The sample code for these notes is available on Github.