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.

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. If clusters and nodes are available, you need not create them again.

Procedure

1. (Optional) If you use a private container image to create your cron job, upload the container image to the image repository.

2. Log in to the CCE console. In the navigation pane, choose Workloads > Cron Jobs. Then, click Create Cron Job.
3. Configure the basic cron job information listed in Table 1. The parameters marked with an asterisk (*) are mandatory.

   Table 1 Basic cron job information

   Parameter	Description
   * Job Name	Name of a new cron job. The name must be unique. Enter 4 to 52 characters starting with a lowercase letter and ending with a letter or digit. Only lowercase letters, digits, and hyphens (-) are allowed.
   * Cluster	Cluster to which a new cron job belongs.
   * Namespace	Namespace to which a cron job belongs. If you do not specify this parameter, the value default is used by default.
   Description	Description of a cron job.

4. Click Next: Configure Timing Rule.
5. Set the timing rule.

   Table 2 Timing rule parameters

   Parameter	Description
   * Concurrency Policy	The following policies are supported: Forbid: A new job cannot be created before the previous job is complete. 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 the job but the previous job is not complete.
   * Schedule	Time when a new cron job is executed.
   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.

6. Click Next: Add Container to add a container.
   1. Click Select Container Image to select the image to be deployed.
      • My Images: displays all image repositories you created.
      • Third-Party Images: Create a job using an image from any third-party image repository. When you create a job using a third-party image, ensure that the node where the job is running can access public networks. For details about how to use a third-party image, see Using a Third-Party Image.
        • If your image repository does not require authentication, set Secret Authentication to No, enter an image address in Image Address, and then click OK.
        • If your image repository must be authenticated (account and password), you need to create a secret and then use a third-party image. For details, see Using a Third-Party Image.
      • Shared Images: The images shared by other tenants using the SWR service are displayed here. You can create workloads based on the shared images.
   2. Set image parameters.

      Table 3 Image parameters

      Parameter	Description
      Image	Name of the image. You can click Change Image to update it.
      *Image Version	Select the image tag to be deployed.
      *Container Name	Name of the container. You can modify it.
      Container Resources	CPU Request: minimum number of CPU cores required by a container. The default value is 0.25 cores. Limit: maximum number of CPU cores available for a container. Do not leave Limit unspecified. Otherwise, intensive use of container resources will occur and your workload may exhibit unexpected behavior. Memory Request: minimum amount of memory required by a container. The default value is 0.5 GiB. Limit: maximum amount of memory available for a container. When memory usage exceeds the specified memory limit, the container will be terminated. For more information about Request and Limit, see Setting Container Specifications. GPU: configurable only when the cluster contains GPU nodes. It indicates the percentage of GPU resources reserved for a container. Select Use and set the percentage. For example, if this parameter is set to 10%, the container is allowed to use 10% of GPU resources. If you do not select Use or set this parameter to 0, no GPU resources can be used. GPU/Graphics Card: The workload's pods will be scheduled to the node with the specified GPU. If Any GPU type is selected, the container uses a random GPU in the node. If you select a specific GPU, the container uses that GPU accordingly.

   3. (Optional) Configure advanced settings.

      Table 4 Advanced settings

      Parameter	Description
      Lifecycle	Actions defined in the lifecycle script definition are taken for the lifecycle events of container tasks. Start Command: You can set the command to be executed immediately after the container is started. For details, see Configuring a Container. Post-Start: The command is triggered after a job starts. For details, see Setting Container Lifecycle Parameters. Pre-Stop: The command is triggered before a job is stopped. For details, see Setting Container Lifecycle Parameters.
      Environment Variables	Environment variables can be added to a container. In general, environment variables are used to set parameters. On the Environment Variables tab page, click Add Environment Variable. Currently, environment variables can be added using any of the following methods: Added manually: Set Variable Name and Variable Value/Reference. Added from Secret: Set Variable Name and select the desired secret name and data. A secret must be created in advance. For details, see Creating a Secret. Added from ConfigMap: Set Variable Name and select the desired ConfigMap name and data. A ConfigMap must be created in advance. For details, see Creating a ConfigMap.

   4. (Optional) One job pod contains one or more related containers. If your cron job contains multiple containers, click Add Container to add containers.

7. Click Create.

   If the status is Started, the cron job has been created successfully.

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.

1. Create a cron job.

   kubectl create -f cronjob.yaml

   Information similar to the following is displayed:

   cronjob.batch/hello created

2. 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

   

   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 5.