README.md

Job

Before using kubectl, please set the KUBECONFIG environment variable to point to the right kubeconfig file.

$ export KUBECONFIG=../02-Multi-node_cluster/vagrant/kubeconfig.yaml

A job in Kubernetes is a supervisor for pods carrying out batch processes, that is, a process that runs for a certain time to completion, for example a calculation or a backup operation.

Let’s create a job called countdown that supervises a pod counting from 9 down to 1:

$ kubectl apply -f job.yaml
job.batch/countdown created

You can see the job and the pod like so:

$ kubectl get jobs
NAME        COMPLETIONS   DURATION   AGE
countdown   1/1           2s         2s

$ kubectl get pods
NAME              READY   STATUS      RESTARTS   AGE
countdown-xjmhc   0/1     Completed   0          75s

To learn more about the status of the job, do:

$ kubectl describe jobs/countdown
Name:           countdown
Namespace:      default
Selector:       controller-uid=18e1ee54-13b3-42ba-b561-42ab030d64bf
Labels:         controller-uid=18e1ee54-13b3-42ba-b561-42ab030d64bf
                job-name=countdown
Annotations:    kubectl.kubernetes.io/last-applied-configuration:
                  {"apiVersion":"batch/v1","kind":"Job","metadata":{"annotations":{},"name":"countdown","namespace":"default"},"spec":{"template":{"metadata...
Parallelism:    1
Completions:    1
Start Time:     Tue, 24 Sep 2019 17:17:25 +0200
Completed At:   Tue, 24 Sep 2019 17:17:27 +0200
Duration:       2s
Pods Statuses:  0 Running / 1 Succeeded / 0 Failed
Pod Template:
  Labels:  controller-uid=18e1ee54-13b3-42ba-b561-42ab030d64bf
           job-name=countdown
  Containers:
   counter:
    Image:      centos:7
    Port:       <none>
    Host Port:  <none>
    Command:
      bin/bash
      -c
      for i in 9 8 7 6 5 4 3 2 1 ; do echo $i ; done
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age    From            Message
  ----    ------            ----   ----            -------
  Normal  SuccessfulCreate  2m51s  job-controller  Created pod: countdown-xjmhc

And to see the output of the job via the pod it supervised, execute:

$ kubectl logs countdown-xjmhc
9
8
7
6
5
4
3
2
1

To clean up, use the delete verb on the job object which will remove all the supervised pods:

$ kubectl delete jobs/countdown
job.batch "countdown" deleted

Let's try to schedule a CronJob. CronJobs are useful to start a computation or activity on pre-defined interval.

To try a CronJob resource apply the cron-job.yaml config.

$ kubectl apply -f cron-job.yaml
cronjob.batch/hello created

To inspect the CronJob schedule:

$ kubectl get cronjob hello
NAME    SCHEDULE      SUSPEND   ACTIVE   LAST SCHEDULE   AGE
hello   */1 * * * *   False     0        <none>          15s

As you can see from the results of the command, the cron job has not scheduled or run any jobs yet. Watch for the job to be created in around one minute:

$ kubectl get jobs --watch
NAME               COMPLETIONS   DURATION   AGE
hello-1569340620   1/1           4s         65s
hello-1569340680   1/1           4s         5s

To delete the CronJob:

$ kubectl delete -f cron-job.yaml
cronjob.batch "hello" deleted