scheduled jobs with kubernetes cronjobs

scheduled jobs with kubernetes cronjobs

what are scheduled jobs?

Scheduled Jobs are automated pieces of work that can be performed at a specific time or on a recurring schedule.

Example use cases:

  • Sending performance metrics on weekly/monthly basis
  • Analyse and send user behaviour metrics to admins on a daily basis

what are cronjobs?

  • A cron job is a Linux command used for scheduling tasks to be executed sometime in the future.
  • This is normally used to schedule a job that is executed periodically
  • Syntax:

# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of the month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday;
# │ │ │ │ │                                   7 is also Sunday on some systems)
# │ │ │ │ │
# │ │ │ │ │
# * * * * *
- will help us with configuration


  • How Kubernetes works and schedules containers as pods
  • How Kubernetes manages objects and config in a declarative way
  • The differences between a service, deployment, and Horizontal Pod Autoscaler
  • Aware of usual Kubernetes terms like Node, Kubelet, and the likes.

kubernetes and cronjobs

  • Kubernetes comes with objects called cronjobs which works similar to the linux cronjobs
  • The timezone is taken from the k8s/kubernetes cluster
  • Cronjobs are a wrapper around kubernetes jobs

simple configuration yaml file for kubernetes cronjob

apiVersion: batch/v1beta1
kind: CronJob
  name: simple-job-name
  schedule: "5 * * * *"
  concurrencyPolicy: Replace
          - name: hello
            image: busybox
            imagePullPolicy: IfNotPresent
            - /bin/sh
            - -c
            - date; echo "Hello from the Kubernetes cluster"
          restartPolicy: OnFailure
  • Above example is simple job which runs every 5 minutes and executes the command
  • We can have multiple containers
  • concurrencyPolicy can have values Allow, Forbid, Replace
    • 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
  • restartPolicy can have values OnFailure, Never

Notes to remember before scheduling the cronjob

  • when restartPolicy is set to OnFailure then it will be restarted if any of the containers failed.
  • It won't follow the sheduled time when it runs for failure.
  • Make sure your command didn't create any issues if it runs at irregular intervals.

Commands to work with kubernets

  • Create the kubernetes cronjob
    kubectl apply -f cronjob.yaml -n namespace
  • Get all scheduled cronjobs
    kubectl get cronjobs -n namespace
  • suspend kubernetes cronjob

    kubectl patch cronjobs <job-name> -p '{"spec" : {"suspend" : true }}' -n namespace

  • delete kubernetes cronjob

    kubectl delete cronjobs <job-name> -n namespace

  • describe a cronjob

    kubectl describe cronjobs <job-name> -n namespace