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.
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
To prepare for this task, perform the following steps:
- Ensure that you have enabled the Google Kubernetes Engine API. Enable Google Kubernetes Engine API
- Ensure that you have installed the Cloud SDK.
- 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]
gcloudto 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
kubectl apply -f [FILENAME].
Specifying when the CronJob runs
spec.schedule field defines when, and how often, the CronJob runs, using
format. All CronJob times are in UTC. There are 5 fields, separated by spaces.
These fields represent the following:
- Minutes (between 0 and 59)
- Hours (between 0 and 23)
- Day of the month (between 1 and 31)
- Month (between 1 and 12)
- Day of the week (between 0 and 6)
You can use the following special characters in any of the
?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
spec.jobTemplate describes what the CronJob does, including its container
images, the commands the containers execute, and the restart policy for the
Specifying a deadline
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
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:
||Concurrent Jobs are allowed. This is the default.|
||Concurrent jobs are forbidden, and new Jobs can't start until previous ones have completed or timed out.|
||Concurrent jobs are forbidden, and old jobs are cancelled in favor of new ones.|
Suspending subsequent executions
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.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 cronjob [CRON_JOB]
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
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 get logs with the name
of the Pod:
kubectl get 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 cronjob [CRON_JOB]
When you delete a CronJob, the Kubernetes garbage collector deletes the associated Jobs and prevents new Jobs from starting.