Running Automated Tasks with a CronJob

This page shows how to run automated tasks using Kubernetes CronJob object.

Before you begin

  • You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Creating a CronJob

Cron jobs require a config file. Here is a manifest for a CronJob that runs a simple demonstration task every minute:

application/job/cronjob.yaml Running Automated Tasks with a CronJob - 图1

  1. apiVersion: batch/v1
  2. kind: CronJob
  3. metadata:
  4.   name: hello
  5. spec:
  6.   schedule: "* * * * *"
  7.   jobTemplate:
  8.     spec:
  9.       template:
  10.         spec:
  11.           containers:
  12.           - name: hello
  13.             image: busybox:1.28
  14.             imagePullPolicy: IfNotPresent
  15.             command:
  16.             - /bin/sh
  17.             - -c
  18.             - date; echo Hello from the Kubernetes cluster
  19.           restartPolicy: OnFailure

Run the example CronJob by using this command:

  1. kubectl create -f https://k8s.io/examples/application/job/cronjob.yaml

The output is similar to this:

  1. cronjob.batch/hello created

After creating the cron job, get its status using this command:

  1. kubectl get cronjob hello

The output is similar to this:

  1. NAME    SCHEDULE      SUSPEND   ACTIVE   LAST SCHEDULE   AGE
  2. hello   */1 * * * *   False     0        <none>          10s

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:

  1. kubectl get jobs --watch

The output is similar to this:

  1. NAME               COMPLETIONS   DURATION   AGE
  2. hello-4111706356   0/1                      0s
  3. hello-4111706356   0/1           0s         0s
  4. hello-4111706356   1/1           5s         5s

Now you’ve seen one running job scheduled by the “hello” cron job. You can stop watching the job and view the cron job again to see that it scheduled the job:

  1. kubectl get cronjob hello

The output is similar to this:

  1. NAME    SCHEDULE      SUSPEND   ACTIVE   LAST SCHEDULE   AGE
  2. hello   */1 * * * *   False     0        50s             75s

You should see that the cron job hello successfully scheduled a job at the time specified in LAST SCHEDULE. There are currently 0 active jobs, meaning that the job has completed or failed.

Now, find the pods that the last scheduled job created and view the standard output of one of the pods.

Note: The job name is different from the pod name.

  1. # Replace "hello-4111706356" with the job name in your system
  2. pods=$(kubectl get pods --selector=job-name=hello-4111706356 --output=jsonpath={.items[*].metadata.name})

Show the pod log:

  1. kubectl logs $pods

The output is similar to this:

  1. Fri Feb 22 11:02:09 UTC 2019
  2. Hello from the Kubernetes cluster

Deleting a CronJob

When you don’t need a cron job any more, delete it with kubectl delete cronjob <cronjob name>:

  1. kubectl delete cronjob hello

Deleting the cron job removes all the jobs and pods it created and stops it from creating additional jobs. You can read more about removing jobs in garbage collection.