Kubernetes - Cron Job

Similar to Jobs kubernetes does have an option to schedule jobs. Kubernetes lets us to use cron job to perform a finite, time related tasks that run once or repeatedly at a time that we specify. Cron jobs can be used for automatic tasks that run on specific time, such as backups , reporting and sending emails.

Cron jobs are based on jobs. they use Job objects to complete their tasks. cron Job creates a job object about once per execution time of the schedule. Cron jobs are created, managed, scaled and deleted in the same way as jobs

lets create a simple cron job using,

[root@manja17-I13330 kubenetes-config]# cat scheduled-jobs.yml

apiVersion: batch/v1beta1

kind: CronJob

metadata:

 name: testing-service

spec:

 schedule: "*/1 * * * *"

 jobTemplate:

   spec:

     template:

       spec:

         containers:

           - name: counter

             image: centos:7

             command:

                - "bin/bash"

                - "-c"

                - "for i in 3 2 1 ; do echo $i ; done"

         restartPolicy: OnFailure

The main element in the above config file is the schedule element.i am creating a pod that will be executed every 1 minute. This generally creates a pod which further creates a container called "counter" that runs a bash for loop.

The pod will be created every 1 minute and run until job is completed.

[root@manja17-I13330 kubenetes-config]# kubectl get jobs --watch

NAME                          DESIRED SUCCESSFUL AGE

testing-service-1526757000   1 0 3s

testing-service-1526757000   1 1 21s

testing-service-1526757060   1 0 0s

testing-service-1526757060   1 0 0s

testing-service-1526757060   1 1 3s

We can see that a pod is being created for every 1 minute which has a container "counter" running the bash for loop. We can get the cron jobs available using,

[root@manja17-I13330 kubenetes-config]# kubectl get cronjobs

NAME               SCHEDULE SUSPEND   ACTIVE LAST SCHEDULE  AGE

testing-service   */1 * * * * False      0 50s   2m

Lets see that the pods are running are not, using

[root@manja17-I13330 kubenetes-config]# kubectl get pods

NAME                                READY STATUS RESTARTS AGE

testing-service-1526757000-gh8bb   0/1 Completed 0 2m

testing-service-1526757060-2t67m   0/1 Completed 0 1m

testing-service-1526757120-z72t6    0/1 Completed 0 25s

Check the logs for each pod as,

[root@manja17-I13330 kubenetes-config]# kubectl logs

testing-service-1526757120-z72t6

3

2

1

[root@manja17-I13330 kubenetes-config]# kubectl logs testing-service-1526757060-2t67m

3

2

1

More to come , happy learning :-)