# CronJob

CronJob 即定时任务，就类似于 Linux 系统的 crontab，在指定的时间周期运行指定的任务。

## API 版本对照表

| Kubernetes 版本 | Batch API 版本   | 默认开启 |
| ------------- | -------------- | ---- |
| v1.5-v1.7     | batch/v2alpha1 | 否    |
| v1.8-v1.20    | batch/v1beta1  | 是    |
| v1.21+        | batch/v1       | 是    |

注意：使用默认未开启的 API 时需要在 kube-apiserver 中配置 `--runtime-config=batch/v2alpha1`。

## CronJob Spec

* `.spec.schedule` 指定任务运行周期，格式同 [Cron](https://en.wikipedia.org/wiki/Cron)
* `.spec.jobTemplate` 指定需要运行的任务，格式同 [Job](https://kubernetes.feisky.xyz/concepts/objects/job)
* `.spec.startingDeadlineSeconds` 指定任务开始的截止期限
* `.spec.concurrencyPolicy` 指定任务的并发策略，支持 Allow、Forbid 和 Replace 三个选项

```yaml
apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            imagePullPolicy: IfNotPresent
            command:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes cluster
          restartPolicy: OnFailure
```

```
$ kubectl create -f cronjob.yaml
cronjob "hello" created
```

当然，也可以用 `kubectl run` 来创建一个 CronJob：

```
kubectl run hello --schedule="*/1 * * * *" --restart=OnFailure --image=busybox -- /bin/sh -c "date; echo Hello from the Kubernetes cluster"
```

```
$ kubectl get cronjob
NAME      SCHEDULE      SUSPEND   ACTIVE    LAST-SCHEDULE
hello     */1 * * * *   False     0         <none>
$ kubectl get jobs
NAME               DESIRED   SUCCESSFUL   AGE
hello-1202039034   1         1            49s
$ pods=$(kubectl get pods --selector=job-name=hello-1202039034 --output=jsonpath={.items..metadata.name} -a)
$ kubectl logs $pods
Mon Aug 29 21:34:09 UTC 2016
Hello from the Kubernetes cluster

# 删除 cronjob 的时候会删除它创建的 job 和 pod，并停止正在创建的 job
$ kubectl delete cronjob hello
cronjob "hello" deleted
```

## 参考文档

* [Cron Jobs](https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/)


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