CronJobs

CronJobs is generally available (GA) in Google Kubernetes Engine (GKE) version 1.21 and later. This document explains how to run CronJobs in GKE. CronJobs are a built-in feature of Kubernetes. For more details, see the Kubernetes documentation about CronJobs.

Overview

CronJobs create Kubernetes Jobs on a repeating schedule. CronJobs allow you to automate regular tasks like making backups, creating reports, sending emails, or cleanup tasks.

A CronJob creates a Job 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:

• Ensure that you have enabled the Google Kubernetes Engine API.
Enable Google Kubernetes Engine API
• Ensure that you have installed the Cloud SDK.

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 for zonal clusters or a region for regional or Autopilot clusters.

Note: You can override these default settings in gcloud commands using the --project, --zone, and --region flags.

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 Autopilot or regional clusters, set your default compute region:

  gcloud config set compute/region COMPUTE_REGION

• Update gcloud to the latest version:

  gcloud components update

Note: You can override these default settings in gcloud commands using the --project, --zone, and --region flags.

Creating a CronJob

You can create a CronJob using a manifest file. For example, the following YAML manifest prints the current time and a string once every minute, while retaining the default values for CronJob parameters:

# cronjob.yaml
apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  concurrencyPolicy: Allow
  startingDeadlineSeconds: 100
  suspend: false
  successfulJobsHistoryLimit: 3
  failedJobsHistoryLimit: 1
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            args:
            - /bin/sh
            - -c
            - date; echo "Hello, World!"
          restartPolicy: OnFailure

To create this CronJob, save the YAML manifest to a file and apply it to the cluster:

kubectl apply -f PATH_TO_FILE

Replace PATH_TO_FILE with the path to the YAML manifest.

Configuring a CronJob

You can specify the following parameters when you create a CronJob:

• When the CronJob runs
• What the CronJob does
• The deadline for the CronJob to start
• Whether concurrent Jobs are allowed for the CronJob
• Whether new Jobs are suspended
• How many executions the CronJob saves in its history

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 five 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 starting on Sunday)

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 example, 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/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  startingDeadlineSeconds: 100
  jobTemplate:
    spec:
    ...

Note: If you specify an empty value for the startingDeadlineSeconds field, the CronJob never times out. This could lead to the same CronJob running multiple times simultaneously. You can prevent this by 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

Replace CRONJOB_NAME with the name of the CronJob to inspect.

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 most recent failed Job. You can change or disable these defaults by changing the CronJob history limits.

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.

Note: You may see more entries than you expect. CronJob history is subject to periodic garbage collection. For example, in the output below, four instances of the hello CronJob are shown.

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

You can cause a Job to fail on purpose by modifying the example manifest in Creating a CronJob. Change the args field in spec.containers to an invalid command or a path that doesn't exist, and change the metadata.name value to one that indicates that you are testing for failures.

To view the logs for a specific CronJob, run the following command:

kubectl logs POD_NAME

Replace POD_NAME with the name of the Pod you want to inspect.

The output is similar to the following:

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, run the following command:

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

• Read the Kubernetes documentation for CronJobs.
• Learn how to run a Job.