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Kubernetes Cronjobs

Kubernetes has the concept of Cronjobs which create Jobs according to a schedule. You can use CronJobs to run tasks at a specific time or interval. CronJobs are a good choice for automatic tasks such as backups, reporting, sending emails, or cleanup tasks.

Usage

CronJobs use Job objects to complete their tasks. A CronJob creates a Job object each time it runs. CronJobs are created, managed, scaled, and deleted in the same way as Jobs. Cron jobs require a config file. Follow this guide to create a Cronjob.

The example cron job below prints the current time and a hello message every first minute of every hour from 0200 to 1400 UTC on Sunday, Monday, Friday, and Saturday:

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "1 2-14 * * 0-1,5-6"
  successfulJobsHistoryLimit: 1
  failedJobsHistoryLimit: 1
  jobTemplate:
    spec:
      ttlSecondsAfterFinished: 100
      template:
        spec:
          containers:
          - name: hello
            image: bitnami/nginx
            args:
            - /bin/sh
            - -c
            - date; echo "Hello, World!"
          restartPolicy: OnFailure

Deploying a Cronjob to your Namespace

You need a yaml file to define your cronjob. You can either create your own, or use this one as an example. This periodically deletes untagged images in the ECR docker image repository (to ensure we stay within the number of images we are allowed).

kubectl apply --filename cronjob-ecr.yaml --namespace [your namespace]

Verify the Cronjob is created:

kubectl get cronjob --namespace [your namespace]

Clean up finished jobs

Jobs created by CronJobs are usually not needed after they have run to completion. Use the TTL mechanism to automatically clean them up by settting ttlSecondsAfterFinished, to tell kubernetes when it can delete the completed Job.

We also have a delete-completed-jobs concourse job which will clean up all completed jobs which do not have ttlSecondsAfterFinished defined.

Deleting completed Jobs cleans up the Pods they create, which helps the kubernetes cluster to use its CPU and memory resources efficiently. You can still see the logs of the deleted Pod in kibana.

Note: Kubernetes uses UTC exclusively. Make sure you take that into account when you’re creating your schedule or defining ttlSecondsAfterFinished.

This page was last reviewed on 21 September 2021. It needs to be reviewed again on 21 December 2021 .
This page was set to be reviewed before 21 December 2021. This might mean the content is out of date.