CronJobs

This page explains how to run CronJobs in Google Kubernetes Engine. CronJobs are a native feature of Kubernetes; for more details, see the Kubernetes documentation about CronJobs.

Overview

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.

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. For more information about Jobs, see Running a Job.

Before you begin

Before you start, make sure you have performed the following tasks:

Set up default gcloud settings using one of the following methods:

  • Using gcloud init, if you want to be walked through setting defaults.
  • Using gcloud config, to individually set your project ID, zone, and region.

Using gcloud init

If you receive the error One of [--zone, --region] must be supplied: Please specify location, complete this section.

  1. Run gcloud init and follow the directions:

    gcloud init

    If you are using SSH on a remote server, use the --console-only flag to prevent the command from launching a browser:

    gcloud init --console-only
  2. Follow the instructions to authorize gcloud to use your Google Cloud account.
  3. Create a new configuration or select an existing one.
  4. Choose a Google Cloud project.
  5. Choose a default Compute Engine zone.

Using gcloud config

  • Set your default project ID:
    gcloud config set project project-id
  • If you are working with zonal clusters, set your default compute zone:
    gcloud config set compute/zone compute-zone
  • If you are working with regional clusters, set your default compute region:
    gcloud config set compute/region compute-region
  • Update gcloud to the latest version:
    gcloud components update

Creating a CronJob

This CronJob prints the current time and a string once per minute:

# cronjob.yaml
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            args:
            - /bin/sh
            - -c
            - date; echo "Hello, World!"
          restartPolicy: OnFailure

To create this CronJob, you can save the YAML manifest to a file and apply it to the cluster using the following command:

kubectl apply -f filename

The next sections provide more details about specifying when the CronJob runs and what actually runs.

Specifying when the CronJob runs

The spec.schedule field defines when, and how often, the CronJob runs, using Unix standard crontab format. All CronJob times are in UTC. There are 5 fields, separated by spaces. These fields represent the following:

  1. Minutes (between 0 and 59)
  2. Hours (between 0 and 23)
  3. Day of the month (between 1 and 31)
  4. Month (between 1 and 12)
  5. Day of the week (between 0 and 6)

You can use the following special characters in any of the spec.schedule fields:

  • ? is a wildcard value that matches a single character.
  • * is a wildcard value that matches zero or more characters.
  • /, allows you to specify an interval for a field. For instance, if the first field (the minutes field) has a value of */5, it means "every 5 minutes". If the fifth field (the day-of-week field) is set to 0/5, it means "every fifth Sunday".

Specifying what the CronJob runs

The spec.jobTemplate describes what the CronJob does, including its container images, the commands the containers execute, and the restart policy for the CronJob. For more details on what to include in the spec.jobTemplate, see the Kubernetes CronJob documentation.

Specifying a deadline

The optional startingDeadlineSeconds field indicates the maximum number of seconds the CronJob can take to start if it misses its scheduled time for any reason. Missed CronJobs are considered failures.

To specify a deadline, add the startingDeadlineSeconds value to the CronJob's spec field in the manifest file. For example, the following manifest specifies that the CronJob has 100 seconds to begin:

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  startingDeadlineSeconds: 100
  jobTemplate:
    spec:
    ...

If you do not specify a startingDeadlineSeconds value, the CronJob never times out. This could lead to the same CronJob running multiple times simultaneously. To prevent this type of problem, see Specifying a concurrency policy.

Specifying a concurrency policy

The optional spec.concurrencyPolicy field specifies how to treat concurrent executions of a Job created by the CronJob controller. If you do not set a value, multiple concurrent Jobs are allowed by default

concurrencyPolicy accepts the following values:

Value Meaning
Allow Concurrent Jobs are allowed. This is the default.
Forbid Concurrent jobs are forbidden, and new Jobs can't start until previous ones have completed or timed out.
Replace Concurrent jobs are forbidden, and old jobs are cancelled in favor of new ones.

Suspending subsequent executions

The optional spec.suspend field, when set to true, prevents new Jobs from being run, but allows current executions to finish.

Specifying history limits

A CronJob creates a Pod each time it runs. Viewing the termination status of a CronJob's recent executions, as well as the logs of an individual Pod, are covered in Viewing CronJob history.

You can configure the number of successful and failed CronJob executions that are saved, by specifying values for spec.successfulJobsHistoryLimit and spec.failedJobsHistoryLimit. By default, successfulJobsHistoryLimit is set to 3 and failedJobsHistoryLimit is set to 1.

To disable retention of data about successful or failed jobs, set the respective value to 0. However, debugging failures may be more difficult.

Inspecting a CronJob

To check a CronJob's configuration, use kubectl describe:

kubectl describe cronjob cronjob-name

Viewing CronJob history

A CronJob runs within a Pod. By default, Kubernetes preserves the logs for terminated Pods representing the last three successful runs of a CronJob and the single last failed job. You can change or disable these defaults.

To view a CronJob's history, first list all Pods. Completed CronJobs are shown with a status of Completed, and failed jobs have a status of RunContainerError, CrashLoopBackOff, or another status indicating a failure.

kubectl get pods

NAME                                READY   STATUS              RESTARTS   AGE
hello-1556555640-9bc5r              0/1     Completed           0          3m6s
hello-1556555700-cm6wk              0/1     Completed           0          2m6s
hello-1556555760-62wf5              0/1     Completed           0          66s
hello-1556555820-rl8kl              0/1     Completed           0          5s
hello-failed-1556555820-wrvt2       0/1     RunContainerError   1          5s

To view the logs for a specific CronJob, use kubectl logs pod-name:

kubectl logs hello-failed-1556555820-wrvt2

container_linux.go:247: starting container process caused
"exec: \"/in/sh\": stat /in/sh: no such file or directory"

Deleting a CronJob

To delete a CronJob, use kubectl delete:

kubectl delete cronjob cronjob-name

When you delete a CronJob, the Kubernetes garbage collector deletes the associated Jobs and prevents new Jobs from starting.

What's next