Kubernetes学习之Crontab控制器

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原创最新推荐文章于 2026-09-22 23:30:05 发布 1k 阅读 AI 写同款· GEO 优化 ›

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一、认识CronJob控制器
　　CronJob控制器用于管理Job控制器资源的运行时间。Job控制器定义的作业任务在其控制器资源创建之后便会立即执行，但是CronJob可以以类似于Linux操作系统中的周期任务作业计划（crontab）的方式控制其运行的时间点及重复运行的方式，具体如下：
　　1）在未来某个时间点运行作业一次
　　2）在指定的时间点重复运行作业
　　CronJob对象支持使用时间格式类似于CronJob，略微有不同的是，CronJob控制器在指定的时间点时，"?“和”*"的意义相同，都表示任何可用的有效值。
在这里插入图片描述

二、创建CronJob对象
　　CronJob控制器的spec字段可嵌套使用以下字段：
　　1）jobTemplate<Object>：Job控制器模板，用于为CronJob控制器生成Job对象；必选字段；
　　2）schedule<string>：Cron格式的作业调度运行时间点；必须字段；
　　3）concurrencyPolicy<string>：并发执行策略，可用的值有"Allow（允许）"、"Forbid(禁止)“和"Replace（替换）”，用于定义前一次作业运行尚未完成时是否以及如何运行后一次作业；
　　4）failedJobHistoryLimit<integer>：为失败的任务执行保留的历史记录数，默认为1；
　　5）successfulJobHistoryLimit<integer>：为成功的任务执行保留的历史记录数，默认为3；
　　6）startingDeadlineSeconds<integer>：因各种原因缺乏执行作业的时间点所导致的启动作业错误的超时时长，会被记入错误历史记录；
　　7）suspend<bollean>：是否挂起后续的任务执行，默认为false，对运行中的作业不会产生影响；

]# cat cronjob.yaml 
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: crontab-example
  labels:
    app: mycronjob
spec:
  schedule: "*/2 * * * *"
  jobTemplate:
    metadata:
      labels:
        app: mycronjob-jobs
    spec:
      parallelism: 2
      template:
        spec:
          containers:
          - name: myjob
            image: alpine
            imagePullPolicy: IfNotPresent
            command: 
            - /bin/sh
            - -c 
            - date; echo Hello from the Kubernetes cluster; sleep 10
          restartPolicy: OnFailure

]# kubectl apply -f cronjob.yaml 
cronjob.batch/crontab-example created

2）查看CronJob控制器信息

]# kubectl get cronjob -o wide 
NAME              SCHEDULE      SUSPEND   ACTIVE   LAST SCHEDULE   AGE   CONTAINERS   IMAGES   SELECTOR
crontab-example   */2 * * * *   False     0        <none>          8s    myjob        alpine   <none>

命令结果的显示：
　　SCHEDULE：是指其调度的时间点
　　SUSPEND：表示后续任务是否处于挂起状态，即暂停任务的调度和运行
　　ACTIVE：表示活动状态的Job对象的数量
　　LAST SCHEDULE：表示上次调度运行至此刻的时长

]# kubectl get pods -o wide  -w 
NAME                               READY   STATUS      RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
crontab-example-1597022880-bj7c8   0/1     Completed   0          71s   10.244.2.30   node2   <none>           <none>
crontab-example-1597022880-nvc4r   0/1     Completed   0          71s   10.244.1.73   node1   <none>           <none>

crontab-example-1597023000-rjfvw   0/1     Pending     0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Pending     0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023000-rjfvw   0/1     Pending     0          0s    <none>        node2    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Pending     0          0s    <none>        node1    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     ContainerCreating   0          0s    <none>        node1    <none>           <none>
crontab-example-1597023000-rjfvw   0/1     ContainerCreating   0          0s    <none>        node2    <none>           <none>
crontab-example-1597023000-g7r5q   1/1     Running             0          1s    10.244.1.74   node1    <none>           <none>
crontab-example-1597023000-rjfvw   1/1     Running             0          1s    10.244.2.31   node2    <none>           <none>
crontab-example-1597023000-rjfvw   0/1     Completed           0          11s   10.244.2.31   node2    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Completed           0          12s   10.244.1.74   node1    <none>           <none>


crontab-example-1597023120-r87rw   0/1     Pending             0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Pending             0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023120-r87rw   0/1     Pending             0          0s    <none>        node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Pending             0          0s    <none>        node1    <none>           <none>
crontab-example-1597023120-r87rw   0/1     ContainerCreating   0          0s    <none>        node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     ContainerCreating   0          0s    <none>        node1    <none>           <none>
crontab-example-1597023120-r87rw   1/1     Running             0          1s    10.244.2.32   node2    <none>           <none>
crontab-example-1597023120-z9gbg   1/1     Running             0          1s    10.244.1.75   node1    <none>           <none>
crontab-example-1597023120-r87rw   0/1     Completed           0          11s   10.244.2.32   node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Completed           0          11s   10.244.1.75   node1    <none>           <none>



]# kubectl get pods -o wide  -w 
NAME                               READY   STATUS      RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
crontab-example-1597022880-bj7c8   0/1     Completed   0          71s   10.244.2.30   node2   <none>           <none>
crontab-example-1597022880-nvc4r   0/1     Completed   0          71s   10.244.1.73   node1   <none>           <none>

crontab-example-1597023000-rjfvw   0/1     Pending     0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Pending     0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023000-rjfvw   0/1     Pending     0          0s    <none>        node2    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Pending     0          0s    <none>        node1    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     ContainerCreating   0          0s    <none>        node1    <none>           <none>
crontab-example-1597023000-rjfvw   0/1     ContainerCreating   0          0s    <none>        node2    <none>           <none>
crontab-example-1597023000-g7r5q   1/1     Running             0          1s    10.244.1.74   node1    <none>           <none>
crontab-example-1597023000-rjfvw   1/1     Running             0          1s    10.244.2.31   node2    <none>           <none>
crontab-example-1597023000-rjfvw   0/1     Completed           0          11s   10.244.2.31   node2    <none>           <none>
crontab-example-1597023000-g7r5q   0/1     Completed           0          12s   10.244.1.74   node1    <none>           <none>


crontab-example-1597023120-r87rw   0/1     Pending             0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Pending             0          0s    <none>        <none>   <none>           <none>
crontab-example-1597023120-r87rw   0/1     Pending             0          0s    <none>        node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Pending             0          0s    <none>        node1    <none>           <none>
crontab-example-1597023120-r87rw   0/1     ContainerCreating   0          0s    <none>        node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     ContainerCreating   0          0s    <none>        node1    <none>           <none>
crontab-example-1597023120-r87rw   1/1     Running             0          1s    10.244.2.32   node2    <none>           <none>
crontab-example-1597023120-z9gbg   1/1     Running             0          1s    10.244.1.75   node1    <none>           <none>
crontab-example-1597023120-r87rw   0/1     Completed           0          11s   10.244.2.32   node2    <none>           <none>
crontab-example-1597023120-z9gbg   0/1     Completed           0          11s   10.244.1.75   node1    <none>           <none>

从观察CronJob控制器与Pod可以看到每隔两分钟都会创建两个并发执行的Pod任务，呆任务完成结束之后便退出状态变成Completed（完成状态）

3）查看CronJob控制器详细信息

]# kubectl describe cronjob crontab-example
Name:                          crontab-example
Namespace:                     default
Labels:                        app=mycronjob
Annotations:                   Schedule:  */2 * * * *
Concurrency Policy:            Allow
Suspend:                       False
Successful Job History Limit:  3
Failed Job History Limit:      1
Starting Deadline Seconds:     <unset>
Selector:                      <unset>
Parallelism:                   2
Completions:                   <unset>
Pod Template:
  Labels:  <none>
  Containers:
   myjob:
    Image:      alpine
    Port:       <none>
    Host Port:  <none>
    Command:
      /bin/sh
      -c
      date; echo Hello from the Kubernetes cluster; sleep 10
    Environment:     <none>
    Mounts:          <none>
  Volumes:           <none>
Last Schedule Time:  Mon, 10 Aug 2020 09:36:00 +0800
Active Jobs:         crontab-example-1597023360
Events:
  Type    Reason            Age    From                Message
  ----    ------            ----   ----                -------
  Normal  SuccessfulCreate  8m9s   cronjob-controller  Created job crontab-example-1597022880
  Normal  SawCompletedJob   7m49s  cronjob-controller  Saw completed job: crontab-example-1597022880, status: Complete
  Normal  SuccessfulCreate  6m9s   cronjob-controller  Created job crontab-example-1597023000
  Normal  SawCompletedJob   5m49s  cronjob-controller  Saw completed job: crontab-example-1597023000, status: Complete
  Normal  SuccessfulCreate  4m9s   cronjob-controller  Created job crontab-example-1597023120
  Normal  SawCompletedJob   3m49s  cronjob-controller  Saw completed job: crontab-example-1597023120, status: Complete
  Normal  SuccessfulCreate  2m9s   cronjob-controller  Created job crontab-example-1597023240
  Normal  SawCompletedJob   109s   cronjob-controller  Saw completed job: crontab-example-1597023240, status: Complete
  Normal  SuccessfulDelete  109s   cronjob-controller  Deleted job crontab-example-1597022880
  Normal  SuccessfulCreate  9s     cronjob-controller  Created job crontab-example-1597023360

三、CronJob的控制机制
　　CronJob控制器是一个更高级别的资源，它以Job控制器资源为其管控对象，并借助它管理Pod资源对象。可列出的Job对象的数量取决于CronJob资源的.spec.successfulJobsHistoryLimit的属性值，默认为3；
　　在这里插入图片描述
　　如果作业重复执行时指定的时间点接近，而作业执行时长（普遍或偶尔）跨过了其两次执行的时间长度，则会出现两个Job对象同时存在的情形。有些Job对象可能会存在无法或不能同时运行的情况，这个时候就要通过.spec.concurrencyPolicy属性控制作业并存的机制，其默认值为"Allow"，即允许前后Job，甚至属于同一个CronJob的更多Job同时运行。其他两个可用值中，"Forbid"用于禁止前后两个Job同时运行，如果前一个尚未结束，后一个则不予启动（跳过），"Replace"用于让后一个Job取代前一个，即终止前一个启动后一个。