How to Create a CronJob in Kubernetes: Step-by-Step Guide

To create a CronJob in Kubernetes, define a YAML manifest specifying the schedule in cron format and the job template to run. Apply this manifest using kubectl apply -f to schedule recurring tasks automatically.

Syntax

A Kubernetes CronJob manifest includes these key parts:

• apiVersion: The API version, usually batch/v1.
• kind: Set to CronJob.
• metadata: Name and labels for the CronJob.
• spec.schedule: The cron expression defining when the job runs.
• spec.jobTemplate: The job to run, including the pod template.

yaml

apiVersion: batch/v1
kind: CronJob
metadata:
  name: example-cronjob
spec:
  schedule: "*/5 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: example
            image: busybox
            args:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes CronJob
          restartPolicy: OnFailure

Example

This example creates a CronJob that runs every 5 minutes. It runs a busybox container that prints the current date and a message.

yaml

apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello-cronjob
spec:
  schedule: "*/5 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            args:
            - /bin/sh
            - -c
            - date; echo Hello from Kubernetes CronJob
          restartPolicy: OnFailure

Output

Every 5 minutes, a job runs and logs output like:
Thu Jun  1 12:00:00 UTC 2024
Hello from Kubernetes CronJob

Common Pitfalls

• Incorrect cron syntax: The schedule must follow standard cron format, or the CronJob won't run.
• Missing restartPolicy: Must be OnFailure or Never for CronJobs.
• Using latest image tag: Avoid it for production; use specific image versions.
• Time zone confusion: Kubernetes uses UTC time for schedules.

yaml

Wrong example:
apiVersion: batch/v1
kind: CronJob
metadata:
  name: bad-cronjob
spec:
  schedule: "60 * * * *"  # Invalid cron expression
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: bad
            image: busybox
            args:
            - /bin/sh
            - -c
            - echo "This will not run"
          restartPolicy: Always  # Invalid for CronJob

Corrected example:
apiVersion: batch/v1
kind: CronJob
metadata:
  name: good-cronjob
spec:
  schedule: "0 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: good
            image: busybox
            args:
            - /bin/sh
            - -c
            - echo "This will run every hour"
          restartPolicy: OnFailure

Quick Reference

Here is a quick cheat sheet for Kubernetes CronJob fields:

Field	Description	Example
apiVersion	API version for CronJob	batch/v1
kind	Resource type	CronJob
metadata.name	Name of the CronJob	my-cronjob
spec.schedule	Cron schedule expression	*/5 * * * *
spec.jobTemplate	Template for the job to run	spec.template.spec.containers
spec.jobTemplate.spec.template.spec.containers[].image	Container image to run	busybox
spec.jobTemplate.spec.template.spec.restartPolicy	Pod restart policy	OnFailure or Never

Key Takeaways

Define a CronJob YAML with schedule and jobTemplate, then apply it with kubectl.

Use valid cron syntax and set restartPolicy to OnFailure or Never.

Kubernetes CronJobs run in UTC time zone by default.

Avoid using the latest image tag for predictable runs.

Check logs of jobs to verify CronJob execution.