Kubernetes v1.21 [stable]
A CronJob creates Jobs on a repeating schedule.
CronJob is meant for performing regular scheduled actions such as backups, report generation, and so on. One CronJob object is like one line of a crontab (cron table) file on a Unix system. It runs a job periodically on a given schedule, written in Cron format.
CronJobs have limitations and idiosyncrasies. For example, in certain circumstances, a single CronJob can create multiple concurrent Jobs. See the limitations below.
When the control plane creates new Jobs and (indirectly) Pods for a CronJob, the
of the CronJob is part of the basis for naming those Pods. The name of a CronJob must be a valid
value, but this can produce unexpected results for the Pod hostnames. For best compatibility,
the name should follow the more restrictive rules for a
Even when the name is a DNS subdomain, the name must be no longer than 52
characters. This is because the CronJob controller will automatically append
11 characters to the name you provide and there is a constraint that the
length of a Job name is no more than 63 characters.
This example CronJob manifest prints the current time and a hello message every minute:
apiVersion: batch/v1 kind: CronJob metadata: name: hello spec: schedule: "* * * * *" jobTemplate: spec: template: spec: containers: - name: hello image: busybox:1.28 imagePullPolicy: IfNotPresent command: - /bin/sh - -c - date; echo Hello from the Kubernetes cluster restartPolicy: OnFailure
(Running Automated Tasks with a CronJob takes you through this example in more detail).
Writing a CronJob spec
.spec.schedule field is required. The value of that field follows the Cron syntax:
# ┌───────────── minute (0 - 59) # │ ┌───────────── hour (0 - 23) # │ │ ┌───────────── day of the month (1 - 31) # │ │ │ ┌───────────── month (1 - 12) # │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday; # │ │ │ │ │ 7 is also Sunday on some systems) # │ │ │ │ │ OR sun, mon, tue, wed, thu, fri, sat # │ │ │ │ │ # * * * * *
0 0 13 * 5 states that the task must be started every Friday at midnight, as well as on the 13th of each month at midnight.
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,
0-23/2can be used in the hours field to specify command execution every other hour (the alternative in the V7 standard is
0,2,4,6,8,10,12,14,16,18,20,22). Steps are also permitted after an asterisk, so if you want to say "every two hours", just use
?) in the schedule has the same meaning as an asterisk
*, that is, it stands for any of available value for a given field.
Other than the standard syntax, some macros like
@monthly can also be used:
|@yearly (or @annually)||Run once a year at midnight of 1 January||0 0 1 1 *|
|@monthly||Run once a month at midnight of the first day of the month||0 0 1 * *|
|@weekly||Run once a week at midnight on Sunday morning||0 0 * * 0|
|@daily (or @midnight)||Run once a day at midnight||0 0 * * *|
|@hourly||Run once an hour at the beginning of the hour||0 * * * *|
To generate CronJob schedule expressions, you can also use web tools like crontab.guru.
.spec.jobTemplate defines a template for the Jobs that the CronJob creates, and it is required.
It has exactly the same schema as a Job, except that
it is nested and does not have an
You can specify common metadata for the templated Jobs, such as
For information about writing a Job
.spec, see Writing a Job Spec.
Deadline for delayed job start
.spec.startingDeadlineSeconds field is optional.
This field defines a deadline (in whole seconds) for starting the Job, if that Job misses its scheduled time
for any reason.
After missing the deadline, the CronJob skips that instance of the Job (future occurrences are still scheduled). For example, if you have a backup job that runs twice a day, you might allow it to start up to 8 hours late, but no later, because a backup taken any later wouldn't be useful: you would instead prefer to wait for the next scheduled run.
For Jobs that miss their configured deadline, Kubernetes treats them as failed Jobs.
If you don't specify
startingDeadlineSeconds for a CronJob, the Job occurrences have no deadline.
.spec.startingDeadlineSeconds field is set (not null), the CronJob
controller measures the time between when a job is expected to be created and
now. If the difference is higher than that limit, it will skip this execution.
For example, if it is set to
200, it allows a job to be created for up to 200
seconds after the actual schedule.
.spec.concurrencyPolicy field is also optional.
It specifies how to treat concurrent executions of a job that is created by this CronJob.
The spec may specify only one of the following concurrency policies:
Allow(default): The CronJob allows concurrently running jobs
Forbid: The CronJob does not allow concurrent runs; if it is time for a new job run and the previous job run hasn't finished yet, the CronJob skips the new job run
Replace: If it is time for a new job run and the previous job run hasn't finished yet, the CronJob replaces the currently running job run with a new job run
Note that concurrency policy only applies to the jobs created by the same cron job. If there are multiple CronJobs, their respective jobs are always allowed to run concurrently.
You can suspend execution of Jobs for a CronJob, by setting the optional
to true. The field defaults to false.
This setting does not affect Jobs that the CronJob has already started.
If you do set that field to true, all subsequent executions are suspended (they remain scheduled, but the CronJob controller does not start the Jobs to run the tasks) until you unsuspend the CronJob.
falseon an existing CronJob without a starting deadline, the missed jobs are scheduled immediately.
Jobs history limits
.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.
For another way to clean up jobs automatically, see Clean up finished jobs automatically.
Kubernetes v1.27 [stable]
For CronJobs with no time zone specified, the kube-controller-manager interprets schedules relative to its local time zone.
You can specify a time zone for a CronJob by setting
.spec.timeZone to the name
of a valid time zone.
For example, setting
.spec.timeZone: "Etc/UTC" instructs Kubernetes to interpret
the schedule relative to Coordinated Universal Time.
A time zone database from the Go standard library is included in the binaries and used as a fallback in case an external database is not available on the system.
Unsupported TimeZone specification
The implementation of the CronJob API in Kubernetes 1.28 lets you set
.spec.schedule field to include a timezone; for example:
CRON_TZ=UTC * * * * *
TZ=UTC * * * * *.
Specifying a timezone that way is not officially supported (and never has been).
If you try to set a schedule that includes
CRON_TZ timezone specification,
Kubernetes reports a warning to the client.
Future versions of Kubernetes will prevent setting the unofficial timezone mechanism entirely.
Modifying a CronJob
By design, a CronJob contains a template for new Jobs. If you modify an existing CronJob, the changes you make will apply to new Jobs that start to run after your modification is complete. Jobs (and their Pods) that have already started continue to run without changes. That is, the CronJob does not update existing Jobs, even if those remain running.
A CronJob creates a Job object approximately once per execution time of its schedule. The scheduling is approximate because there are certain circumstances where two Jobs might be created, or no Job might be created. Kubernetes tries to avoid those situations, but does not completely prevent them. Therefore, the Jobs that you define should be idempotent.
startingDeadlineSeconds is set to a large value or left unset (the default)
concurrencyPolicy is set to
Allow, the jobs will always run
at least once.
startingDeadlineSecondsis set to a value less than 10 seconds, the CronJob may not be scheduled. This is because the CronJob controller checks things every 10 seconds.
For every CronJob, the CronJob Controller checks how many schedules it missed in the duration from its last scheduled time until now. If there are more than 100 missed schedules, then it does not start the job and logs the error.
Cannot determine if job needs to be started. Too many missed start time (> 100). Set or decrease .spec.startingDeadlineSeconds or check clock skew.
It is important to note that if the
startingDeadlineSeconds field is set (not
nil), the controller counts how many missed jobs occurred from the value of
startingDeadlineSeconds until now rather than from the last scheduled time until now. For example, if
200, the controller counts how many missed jobs occurred in the last 200 seconds.
A CronJob is counted as missed if it has failed to be created at its scheduled time. For example, if
concurrencyPolicy is set to
Forbid and a CronJob was attempted to be scheduled when there was a previous schedule still running, then it would count as missed.
For example, suppose a CronJob is set to schedule a new Job every one minute beginning at
08:30:00, and its
startingDeadlineSeconds field is not set. If the CronJob controller happens to
be down from
10:21:00, the job will not start as the number of missed jobs which missed their schedule is greater than 100.
To illustrate this concept further, suppose a CronJob is set to schedule a new Job every one minute beginning at
08:30:00, and its
startingDeadlineSeconds is set to 200 seconds. If the CronJob controller happens to
be down for the same period as the previous example (
10:21:00,) the Job will still start at 10:22:00. This happens as the controller now checks how many missed schedules happened in the last 200 seconds (i.e., 3 missed schedules), rather than from the last scheduled time until now.
The CronJob is only responsible for creating Jobs that match its schedule, and the Job in turn is responsible for the management of the Pods it represents.
- Learn about Pods and Jobs, two concepts that CronJobs rely upon.
- Read about the detailed format
- For instructions on creating and working with CronJobs, and for an example of a CronJob manifest, see Running automated tasks with CronJobs.
CronJobis part of the Kubernetes REST API. Read the CronJob API reference for more details.