You can use CronJobs to run jobs on a time-based schedule. These automated jobs run like Cron tasks on a Linux or UNIX system.
Cron jobs are useful for creating periodic and recurring tasks, like running backups or sending emails. Cron jobs can also schedule individual tasks for a specific time, such as if you want to schedule a job for a low activity period.
Note: CronJob resource inbatch/v2alpha1
API group has been deprecated starting from cluster version 1.8. You should switch to usingbatch/v1beta1
, instead, which is enabled by default in the API server. Examples in this document usebatch/v1beta1
in all examples.
Cron jobs have limitations and idiosyncrasies. For example, in certain circumstances, a single cron job can create multiple jobs. Therefore, jobs should be idempotent. For more limitations, see CronJobs.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
To check the version, enter kubectl version
.
batch/v2alpha1
API by passing --runtime-config=batch/v2alpha1=true
to
the API server (see Turn on or off an API version for your cluster
for more), and then restart both the API server and the controller manager
component.Cron jobs require a config file.
This example cron job config .spec
file prints the current time and a hello message every minute:
application/job/cronjob.yaml
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Run the example CronJob by using this command:
kubectl create -f https://k8s.io/examples/application/job/cronjob.yaml
cronjob.batch/hello created
Alternatively, you can use kubectl run
to create a cron job without writing a full config:
kubectl run hello --schedule="*/1 * * * *" --restart=OnFailure --image=busybox -- /bin/sh -c "date; echo Hello from the Kubernetes cluster"
cronjob.batch/hello created
After creating the cron job, get its status using this command:
kubectl get cronjob hello
NAME SCHEDULE SUSPEND ACTIVE LAST SCHEDULE AGE
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:
kubectl get jobs --watch
NAME COMPLETIONS DURATION AGE
hello-4111706356 0/1 0s
hello-4111706356 0/1 0s 0s
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:
kubectl get cronjob hello
NAME SCHEDULE SUSPEND ACTIVE LAST SCHEDULE AGE
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 and pod name are different.
# Replace "hello-4111706356" with the job name in your system
pods=$(kubectl get pods --selector=job-name=hello-4111706356 --output=jsonpath={.items..metadata.name})
Check pod name:
echo $pods
The output is similar to this:
hello-4111706356-o9qcm
Show pod log:
kubectl logs $pods
The output is similar to this:
Fri Feb 22 11:02:09 UTC 2019
Hello from the Kubernetes cluster
When you don’t need a cron job any more, delete it with kubectl delete cronjob
:
kubectl delete cronjob hello
cronjob.batch "hello" deleted
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.
As with all other Kubernetes configs, a cron job needs apiVersion
, kind
, and metadata
fields. For general
information about working with config files, see deploying applications,
and using kubectl to manage resources documents.
A cron job config also needs a .spec
section.
Note: All modifications to a cron job, especially its.spec
, are applied only to the following runs.
The .spec.schedule
is a required field of the .spec
.
It takes a Cron format string, such as 0 * * * *
or @hourly
, as schedule time of its jobs to be created and executed.
The format also includes extended vixie cron
step values. As explained in the FreeBSD manual:
Step values can be used in conjunction with ranges. Following a range with
/<number>
specifies skips of the number’s value through the range. For example,0-23/2
can be used in the hours field to specify command execution every other hour (the alternative in the V7 standard is0,2,4,6,8,10,12,14,16,18,20,22
). Steps are also permitted after an asterisk, so if you want to say “every two hours”, just use*/2
.
Note: A question mark (?
) in the schedule has the same meaning as an asterisk*
, that is, it stands for any of available value for a given field.
The .spec.jobTemplate
is the template for the job, and it is required.
It has exactly the same schema as a Job, except that it is nested and does not have an apiVersion
or kind
.
For information about writing a job .spec
, see Writing a Job Spec.
The .spec.startingDeadlineSeconds
field is optional.
It stands for the deadline in seconds for starting the job if it misses its scheduled time for any reason.
After the deadline, the cron job does not start the job.
Jobs that do not meet their deadline in this way count as failed jobs.
If this field is not specified, the jobs have no deadline.
The CronJob controller counts how many missed schedules happen for a cron job. If there are more than 100 missed
schedules, the cron job is no longer scheduled. When .spec.startingDeadlineSeconds
is not set, the CronJob
controller counts missed schedules from status.lastScheduleTime
until now. For example, one cron job is
supposed to run every minute, the status.lastScheduleTime
of the cronjob is 5:00am, but now it’s 7:00am.
That means 120 schedules were missed, so the cron job is no longer scheduled. If the .spec.startingDeadlineSeconds
field is set (not null), the CronJob controller counts how many missed jobs occurred from the value of
.spec.startingDeadlineSeconds
until now. For example, if it is set to 200
, it counts how many missed
schedules occurred in the last 200 seconds. In that case, if there were more than 100 missed schedules in the
last 200 seconds, the cron job is no longer scheduled.
The .spec.concurrencyPolicy
field is also optional.
It specifies how to treat concurrent executions of a job that is created by this cron job.
the spec may specify only one of the following concurrency policies:
Allow
(default): The cron job allows concurrently running jobsForbid
: 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 runReplace
: 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 runNote that concurrency policy only applies to the jobs created by the same cron job. If there are multiple cron jobs, their respective jobs are always allowed to run concurrently.
The .spec.suspend
field is also optional.
If it is set to true
, all subsequent executions are suspended.
This setting does not apply to already started executions.
Defaults to false.
Caution: Executions that are suspended during their scheduled time count as missed jobs. When.spec.suspend
changes fromtrue
tofalse
on an existing cron job without a starting deadline, the missed jobs are scheduled immediately.
The .spec.successfulJobsHistoryLimit
and .spec.failedJobsHistoryLimit
fields are optional.
These fields specify how many completed and failed jobs should be kept.
By default, they are set to 3 and 1 respectively. Setting a limit to 0
corresponds to keeping none of the corresponding kind of jobs after they finish.
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