Creating a Cron Job¶

Scenario¶

A cron job runs on a repeating schedule. You can perform time synchronization for all active nodes at a fixed time point.

A cron job runs periodically at the specified time. It is similar with Linux crontab. A cron job has the following characteristics:

Runs only once at the specified time.
Runs periodically at the specified time.

The typical usage of a cron job is as follows:

Schedules jobs at the specified time.
Creates jobs to run periodically, for example, database backup and email sending.

Prerequisites¶

Resources have been created. For details, see Creating a Node.

Using the CCE Console¶

Log in to the CCE console.
Click the cluster name to go to the cluster console, choose Workloads in the navigation pane, and click the Create Workload in the upper right corner.
Set basic information about the workload.
Basic Info
- Workload Type: Select Cron Job. For details about workload types, see Overview.
- Workload Name: Enter the name of the workload. Enter 1 to 52 characters starting with a lowercase letter and ending with a letter or digit. Only lowercase letters, digits, and hyphens (-) are allowed.
- Namespace: Select the namespace of the workload. The default value is default. You can also click Create Namespace to create one. For details, see Creating a Namespace.
- Container Runtime: A CCE cluster uses runC by default, whereas a CCE Turbo cluster supports both runC and Kata. For details about the differences between runC and Kata, see Kata Containers and Common Containers.
Container Settings
- Container Information
  Multiple containers can be configured in a pod. You can click Add Container on the right to configure multiple containers for the pod.
  - Basic Info: See Setting Basic Container Information.
  - Lifecycle: See Setting Container Lifecycle Parameters.
  - Environment Variables: See Setting an Environment Variable.
- Image Access Credential: Select the credential used for accessing the image repository. The default value is default-secret. You can use default-secret to access images in SWR. For details about default-secret, see default-secret.
- GPU graphics card: All is selected by default. The workload instance will be scheduled to the node with the specified GPU graphics card type.
Schedule
- Concurrency Policy: The following three modes are supported:
  - Forbid: A new job cannot be created before the previous job is completed.
  - Allow: The cron job allows concurrently running jobs, which preempt cluster resources.
  - Replace: A new job replaces the previous job when it is time to create a job but the previous job is not completed.
- Policy Settings: specifies when a new cron job is executed. Policy settings in YAML are implemented using cron expressions.
  - A cron job is executed at a fixed interval. The unit can be minute, hour, day, or month. For example, if a cron job is executed every 30 minutes, the cron expression is */30 * * * *, the execution time starts from 0 in the unit range, for example, 00:00:00, 00:30:00, 01:00:00, and ....
  - The cron job is executed at a fixed time (by month). For example, if a cron job is executed at 00:00 on the first day of each month, the cron expression is 0 0 1 */1 *, and the execution time is **-01-01 00:00:00**, **-02-01 00:00:00**, and ....
  - The cron job is executed at a fixed time (by week). For example, if a cron job is executed at 00:00 every Monday, the cron expression is 0 0 * * 1, and the execution time is **--01 00:00:00 on Monday, **--08 00:00:00 on Monday, and ....
  - For details about how to use cron expressions, see cron.
  Note
  - If a cron job is executed at a fixed time (by month) and the number of days in a month does not exist, the cron job will not be executed in this month. For example, if the number of days is set to 30 but February does not have the 30th day, the cron job skips this month and continues on March 30.
  - Due to the definition of the cron expression, the fixed period is not a strict period. The time unit range is divided from 0 by period. For example, if the unit is minute, the value ranges from 0 to 59. If the value cannot be exactly divided, the last period is reset. Therefore, an accurate period can be represented only when the period can evenly divide its time unit range.
    For example, the unit of the period is hour. Because /2, /3, /4, /6, /8, and /12 can be divided by 24, the accurate period can be represented. If another period is used, the last period will be reset at the beginning of a new day. For example, if the cron expression is * */12 * * *, the execution time is 00:00:00 and 12:00:00 every day. If the cron expression is * */13 * * *, the execution time is 00:00:00 and 13:00:00 every day. At 00:00 on the next day, the execution time is updated even if the period does not reach 13 hours.
- Job Records: You can set the number of jobs that are successfully executed or fail to be executed. Setting a limit to 0 corresponds to keeping none of the jobs after they finish.
Advanced Settings
- Labels and Annotations: See Pod Labels and Annotations.
Click Create Workload in the lower right corner.

Using kubectl¶

A cron job has the following configuration parameters:

.spec.schedule: takes a Cron format string, for example, 0 * * * * or @hourly, as schedule time of jobs to be created and executed.
.spec.jobTemplate: specifies jobs to be run, and has the same schema as when you are Creating a Job Using kubectl.
.spec.startingDeadlineSeconds: specifies the deadline for starting a job.
.spec.concurrencyPolicy: specifies how to treat concurrent executions of a job created by the Cron job. The following options are supported:
- Allow (default value): allows concurrently running jobs.
- Forbid: forbids concurrent runs, skipping next run if previous has not finished yet.
- Replace: cancels the currently running job and replaces it with a new one.

The following is an example cron job, which is saved in the cronjob.yaml file.

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 from the Kubernetes cluster
          restartPolicy: OnFailure

Run the job.

Create a cron job.
kubectl create -f cronjob.yaml
Information similar to the following is displayed:
```
cronjob.batch/hello created
```

Query the running status of the cron job:

kubectl get cronjob

NAME      SCHEDULE      SUSPEND   ACTIVE    LAST SCHEDULE   AGE
hello     */1 * * * *   False     0         <none>          9s

kubectl get jobs

NAME               COMPLETIONS   DURATION   AGE
hello-1597387980   1/1           27s        45s

kubectl get pod

NAME                           READY     STATUS      RESTARTS   AGE
hello-1597387980-tjv8f         0/1       Completed   0          114s
hello-1597388040-lckg9         0/1       Completed   0          39s

kubectl logs hello-1597387980-tjv8f

Fri Aug 14 06:56:31 UTC 2020
Hello from the Kubernetes cluster

kubectl delete cronjob hello

cronjob.batch "hello" deleted

Important

When a cron job is deleted, the related jobs and pods are deleted too.

Related Operations¶

After a cron job is created, you can perform operations listed in Table 1.

**Table 1** Other operations¶
Operation	Description
Editing a YAML file	Click More > Edit YAML next to the cron job name to edit the YAML file of the current job.
Stopping a cron job	Select the job to be stopped and click Stop in the Operation column. Click Yes.
Deleting a cron job	Select the cron job to be deleted and click More > Delete in the Operation column. Click Yes. Deleted jobs cannot be restored. Therefore, exercise caution when deleting a job.

last updated: 2023-12-08 00:45