[Kubernetes] Jobs & CronJobs

A Job creates one or more pods and will continue to retry execution of the Pods until a specified number of them successfully terminate. As pods successfully complete, the Job tracks the successful completions. When the specified number of successful completions is reached, the job is complete.

Jobs

A job runs container workloads until they complete, then shuts down the container(s).

Pod backoff failure policy

• Specify a non-zero positive number to “spec.completions”
  • The job is regarded as completed when there are the specified number of successful pods.
  • The default is 1.
• By default, a new pod will created once the pod succeeds or fails. If you want to run multiple pods at once, you can specify “spec.parallelism”
  • The default is 1.
• Set “spec.backoffLimit” to specify the number of retries before considering a Job as failed.
  • The back-off limit is set by default to 6.
• Set “spec.activeDeadlineSeconds” to automatically terminate the job.
  • Once a Job reaches activeDeadlineSeconds, all of its running Pods are terminated and the Job status will become type: Failed
• .spec.activeDeadlineSeconds takes precedence over its .spec.backoffLimit.
• The restartPolicy for a job must be “OnFailure” or “Never“.

apiVersion: batch/v1
kind: Job
metadata:
  name: my-job
spec:
  completions: 4
  parallelism: 2
  activeDeadlineSeconds: 30 
  backoffLimit: 4
  template:
    spec:
      containers:
      - name: job-container
        image: busybox
        command: ['echo', 'Hello World']
      restartPolicy: Never

kubectl create job my-job --image=busybox --dry-run=client -o=yaml > job.yaml

# modify job.yaml

kubectl apply –f my-job.yaml

kubectl get jobs

kubectl describe job <job-name>

kubectl get pods –-selector=job-name=<job-name>
kubectl get pods –l=job-name=<job-name>

kubectl logs <pod-name>

kubectl delete job <job-name>

CronJobs

A CronJob re-runs a job periodically according to a schedule.

spec.schedule

The schedule consists of 5 components

• minute (0 – 59)
• hour (0 – 23)
• day of the month (1 – 31)
• month (1 – 12)
• day of the week (0, Sunday – 6, Saturday)

• The restartPolicy for a cron job must be “OnFailure” or “Never“.

apiVersion: batch/v1
kind: CronJob
metadata:
  name: my-cronjob
spec:
  schedule: "*/1 * * * *"  # every minute
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: job-container
            image: busybox
            command: ['/bin/sh', '-c', 'date']
          restartPolicy: OnFailure

kubectl create cj my-cronjob --image=busybox --schedule="*/1 * * * *" --dry-run=client -o=yaml > my-cronjob.yaml

# modify my-cronjob.yaml

kubectl apply –f my-cronjob.yaml

kubectl get cronjobs

# check the event and find the job name
kubectl describe cronjob <cronjob-name>

kubectl get pods 

kubectl logs <pod-name>

kubectl delete cronjob <cronjob-name>