Jobs

A job creates one or more pods and ensures that a specified number of them successfully terminate. As pods successfully complete, the job tracks the successful completions.

When a specified number of successful completions is reached, the job itself is complete.

Deleting a Job will cleanup the pods it created.

• Start a Job to print date

$ kubectl run date-print --image=ansilh/debug-tools  --restart=OnFailure  -- /bin/sh -c date

$ kubectl get jobs

Output

NAME         COMPLETIONS   DURATION   AGE
date-print   0/1           3s         3s

$ kubectl get pods

Output

NAME               READY   STATUS      RESTARTS   AGE
date-print-psxw6   0/1     Completed   0          8s

$ kubectl get jobs

Output

NAME         COMPLETIONS   DURATION   AGE
date-print   1/1           4s         10s

$ kubectl logs date-print-psxw6

Output

Sun Feb  3 18:10:45 UTC 2019

To control the number of failure and restart , we can use spec.backoffLimit

To start n number of pods that will run in sequential order , we can use ``.spec.completions`

To start multiple pods in parallel , we can use .spec.parallelism

To cleanup the completed Jobs automatically , we can use ttlSecondsAfterFinished (1.12 alpha feature)

https://kubernetes.io/docs/concepts/workloads/controllers/jobs-run-to-completion/

CronJob

CronJob is another abstraction of Job , which will create Job objects periodically based on the mentioned schedule. The schedule notation is taken from Linux cron scheduler

$ kubectl run date-print --image=ansilh/debug-tools  --restart=OnFailure  --schedule="* * * * *" -- /bin/sh -c date

$ kubectl get cronjobs.batch

NAME         SCHEDULE    SUSPEND   ACTIVE   LAST SCHEDULE   AGE
date-print   * * * * *   False     0        <none>          7s

$ kubectl get pods

No resources found.

$ kubectl get cronjobs.batch

NAME         SCHEDULE    SUSPEND   ACTIVE   LAST SCHEDULE   AGE
date-print   * * * * *   False     0        22s             60s

$ kubectl get pods
NAME                          READY   STATUS      RESTARTS   AGE
date-print-1549217580-qmjxt   0/1     Completed   0          36s

$ kubectl logs date-print-1549217580-qmjxt

Sun Feb  3 18:13:08 UTC 2019

Concurrency Policy

The ``.spec.concurrencyPolicy` field is also optional.

It specifies how to treat concurrent executions of a job that is created by this cron job. the spec may specify only one of the following concurrency policies:

Allow (default): The cron job allows concurrently running jobs

Forbid: The cron job does not allow concurrent runs; if it is time for a new job run and the previous job run hasn’t finished yet, the cron job skips the new job run

Replace: If it is time for a new job run and the previous job run hasn’t finished yet, the cron job replaces the currently running job run with a new job run

Note that concurrency policy only applies to the jobs created by the same cron job.

https://kubernetes.io/docs/tasks/job/automated-tasks-with-cron-jobs/