Kubernetes - Repeatable Job

There may be cases where you want to run a program repeatedly. It is very use full to run a program at certain times repeatedly to check something or perform some other actions

Lets create a basic repeatable job manifest file,

[root@manja17-I13330 kubenetes-config]# cat basic-repeatable-job.yml

apiVersion: batch/v1

kind: Job

metadata:

  name: testing-service

spec:

  completions: 3

  template:

    metadata:

      labels:

        name: testing-service

    spec:

      containers:

      - name: counter

        image: centos:7

        command:

          - "bin/bash"

          - "-c"

          - "for i in 9 8 7 6 5 4 3 2 1 ; do echo $i ; done"

      restartPolicy: Never

The important element is the completions: 3 which tells to run the job until completed for 3 times

[root@manja17-I13330 kubenetes-config]# kubectl create -f basic-repeatable-job.yml

job.batch "testing-service" created

[root@manja17-I13330 kubenetes-config]# kubectl get pods

NAME                       READY      STATUS                 RESTARTS   AGE

testing-service-strtz   0/1          ContainerCreating   0                3s

[root@manja17-I13330 kubenetes-config]# kubectl get pods

NAME                          READY     STATUS                 RESTARTS   AGE

testing-service-dpwr2   0/1          ContainerCreating   0               2s

testing-service-strtz     0/1          Completed              0               6s

[root@manja17-I13330 kubenetes-config]# kubectl get pods

NAME                          READY     STATUS      RESTARTS   AGE

testing-service-7vrx5    0/1          Completed   0              4s

testing-service-dpwr2   0/1          Completed   0              6s

testing-service-strtz      0/1          Completed   0             10s

If we see the above pods, we see that they are created one after another and as defined ran a bash command. Lets see the job status ,

[root@manja17-I13330 kubenetes-config]# kubectl get jobs

NAME              DESIRED   SUCCESSFUL   AGE

testing-service   3               3                   1m

Now if we describe the job, we can see

[root@manja17-I13330 kubenetes-config]# kubectl describe job testing-service

Name:           testing-service

Namespace:      default

Selector:       controller-uid=be5f8b69-8f0c-11e8-a791-020055e1ea1d

Labels:         controller-uid=be5f8b69-8f0c-11e8-a791-020055e1ea1d

                job-name=testing-service

                name=testing-service

Annotations:    <none>

Parallelism:    1

Completions:    3

Start Time:     Tue, 24 Jul 2018 02:42:33 -0400

Pods Statuses:  0 Running / 3 Succeeded / 0 Failed

Pod Template:

  Labels:  controller-uid=be5f8b69-8f0c-11e8-a791-020055e1ea1d

           job-name=testing-service

           name=testing-service

  Containers:

   counter:

    Image:      centos:7

    Port:       <none>

    Host Port:  <none>

    Command:

      bin/bash

      -c

      for i in 9 8 7 6 5 4 3 2 1 ; do echo $i ; done

    Environment:  <none>

    Mounts:       <none>

  Volumes:        <none>

Events:

  Type    Reason            Age   From            Message

  ----    ------            ----  ----            -------

  Normal  SuccessfulCreate  1m    job-controller  Created pod: testing-service-strtz

  Normal  SuccessfulCreate  1m    job-controller  Created pod: testing-service-dpwr2

  Normal  SuccessfulCreate  1m    job-controller  Created pod: testing-service-7vrx5

We can check logs for each pod and we can see that the bash command ran as defined. If we set a for repeatable job, the pods run one after the other to perform a job defined until completion.