Jobs and Cron Jobs

Overview

In Kubernetes, there are two types of jobs: one-off jobs and cron jobs.

A job (one-off job) is a resource object that Kubernetes uses to control batch tasks. Jobs are different from long-term servo tasks (such as Deployments and StatefulSets). The former are started and terminated at specific times, while the latter run unceasingly unless being terminated. The pods managed by a job automatically exit after successfully completing the job based on user configurations. The success flag varies depending on the spec.completions policy. A single-pod job is considered successful if one pod completes successfully. A job with a fixed success count is considered successful if N pods complete successfully. A queue job is considered successful based on the global success confirmed by the application.

Similar to a crontab in Linux OS, a cron job can:

Run a scheduled job once at the specified time.
Run a scheduled job 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.

Creating a Job

A job runs pods that perform a completable task. The pods automatically exit after successfully completing the task. Before creating a workload, you can run a job to upload an image to the image repository.

(Optional) If you use a private container image to create your job, upload the container image to the image repository.
On the cluster details page, choose Workloads > Jobs and click Create from Image.

Set basic workload parameters.

Basic Info

Workload Type: Select Job.
Workload Name: Enter a workload name.
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.
Pods: Enter the number of pods.

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 Table 1.

**Table 1** Basic information parameters
Parameter	Description
Container Name	Name the container.
Image Name	Click Select Image and select the image used by the container. My Images: images in the image repository of the current region. If no image is available, click Upload Image to upload an image. Open Source Images: official images in the open source image repository. Shared Images: private images shared by another account. For details, see Sharing Private Images.
Image Tag	Select the image tag to be deployed.
Pull Policy	Image update or pull policy. If you select Always, the image is pulled from the image repository each time. If you do not select Always, the existing image of the node is preferentially used. If the image does not exist in the node, it is pulled from the image repository.
CPU Quota	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 Quota	Request: minimum amount of memory required by a container. The default value is 512 MiB. Limit: maximum amount of memory available for a container. When memory usage exceeds the specified memory limit, the container will be terminated. For details about Request and Limit of CPU or memory, see Setting Container Specifications.
Init Container	Select whether to use the container as an init container. An init container is a special container that runs before app containers in a pod. For details, see Init Containers.
Privileged Container	Programs in a privileged container have certain privileges. If Privileged Container is enabled, the container is assigned privileges. For example, privileged containers can manipulate network devices on the host machine and modify kernel parameters.

Lifecycle: The lifecycle callback functions can be called in specific phases of the container. For example, if you want the container to perform a certain operation before stopping, set the corresponding function. Currently, lifecycle callback functions, such as startup, post-start, and pre-stop are provided. For details, see Setting Container Lifecycle Parameters.
Environment Variable: Environment variables affect the way a running container will behave. Configuration items set by environment variables will not change if the pod lifecycle ends. For details, see Setting Environment Variables.
Data Storage: Store container data using Local Volumes and PersistentVolumeClaims (PVCs). You are advised to use PVCs to store workload pod data on a cloud volume. If you store pod data on a local volume and a fault occurs on the node, the data cannot be restored. For details about container storage, see Container Storage.

Image Access Credential: Select the credential for accessing the image repository. This credential is used only for accessing a private image repository. If the selected image is a public image, you do not need to select a secret. For details on how to create a secret, see Creating a Secret.

Advanced Settings

Labels and Annotations: You can click Confirm to add a label or annotation for the pod. The key of the new label or annotation cannot be the same as that of an existing one.
Job Settings
- Parallel Pods: Maximum number of pods that can run in parallel during job execution. The value cannot be greater than the total number of pods in the job.
- Timeout (s): Once a job reaches this time, the job status becomes failed and all pods in this job will be deleted. If you leave this parameter blank, the job will never time out.

After the job is created, you can view the job in the job list.

If the status of the job is Processing, the job has been created successfully.

Creating a Cron Job

A cron job can run a scheduled job once or periodically at the specified time. The job automatically exits after successfully completing the task. For example, you can perform time synchronization for all active nodes at the specified time.

(Optional) If you use a private container image to create your cron job, upload the container image to the image repository.
On the cluster details page, choose Workloads > Cron Jobs, and click Create Workload.

Configure workload parameters.

Basic Info

Workload Type: Select Cron Job.
Workload Name: Enter a workload name.
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 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 Table 2.

**Table 2** Basic information parameters
Parameter	Description
Container Name	Name the container.
Image Name	Click Select Image and select the image used by the container. My Images: images in the image repository of the current region. If no image is available, click Upload Image to upload an image. Open Source Images: official images in the open source image repository. Shared Images: private images shared by another account. For details, see Sharing Private Images.
Image Tag	Select the image tag to be deployed.
Pull Policy	Image update or pull policy. If you select Always, the image is pulled from the image repository each time. If you do not select Always, the existing image of the node is preferentially used. If the image does not exist in the node, it is pulled from the image repository.
CPU Quota	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 Quota	Request: minimum amount of memory required by a container. The default value is 512 MiB. Limit: maximum amount of memory available for a container. When memory usage exceeds the specified memory limit, the container will be terminated. For details about Request and Limit of CPU or memory, see Setting Container Specifications.
Init Container	Select whether to use the container as an init container. An init container is a special container that runs before app containers in a pod. For details, see Init Containers.
Privileged Container	Programs in a privileged container have certain privileges. If Privileged Container is enabled, the container is assigned privileges. For example, privileged containers can manipulate network devices on the host machine and modify kernel parameters.

Lifecycle: The lifecycle callback functions can be called in specific phases of the container. For example, if you want the container to perform a certain operation before stopping, set the corresponding function. Currently, lifecycle callback functions, such as startup, post-start, and pre-stop are provided. For details, see Setting Container Lifecycle Parameters.
Environment Variable: Environment variables affect the way a running container will behave. Configuration items set by environment variables will not change if the pod lifecycle ends. For details, see Setting Environment Variables.

Image Access Credential: Select the credential for accessing the image repository. This credential is used only for accessing a private image repository. If the selected image is a public image, you do not need to select a secret. For details on how to create a secret, see Creating a Secret.

Execution Settings

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: If it is time for a new job run and the previous job run has not finished yet, the cron job replaces the currently running job run with a new job run.
Policy Settings: Time when a new cron job is executed. Scheduled rules in YAML are implemented using the cron expression.
- 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 and the corresponding 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 by month. For example, if a cron job is executed at 00:00 on the first day of each month, the corresponding 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 by week. For example, if a cron job is executed at 00:00 every Monday, the corresponding cron expression is 0 0 * * 1, and the execution time is ****-**-01 00:00:00 on Monday, ****-**-08 00:00:00 on Monday, and ....
- Custom Cron Expression: For details about how to use cron expressions, see cron.
- If a cron job is executed at a fixed time (by month) and the number of days in a month does not exist, the job will not be executed that month. For example, the execution will skip February if the date is set to 30.
- Due to the definition of cron, the fixed period is not a strict period. The time is divided starting 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 will be reset. Therefore, an accurate period can be represented only when the period can be evenly divided.
  Take a cron job that is executed by hour as an example. As /2, /3, /4, /6, /8, and /12 can exactly divide 24 hours, an 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. Setting a limit to 0 corresponds to keeping none of the jobs after they are completed.

Advanced Settings

Labels and Annotations: You can click Confirm to add a label or annotation for the pod. The key of the new label or annotation cannot be the same as that of an existing one.

After the cron job is created, you can view the cron job in the cron job list.

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

Related Operations

View Events: You can set search criteria, such as the time segment during which an event is generated or the event name, to view related events.
Pods/Jobs: View the information about the target pod/job.
- View Events: Event information generated by the pod, which is stored for one hour.
- Pods: View the pod name, status, and restart times.
- View YAML: View the YAML file of the pod.
- Delete: Delete the pod.
View/Edit YAML: View or edit the YAML file of the workload.
Delete: Delete the workload.
Stop (for cron jobs only): Stop a cron job.