skip to content
Astro Cactus

Jobs and CronJobs in Kubernetes

/ 3 min read

kubernetes , k8s , jobs , cronjobs , devops , cloud-native , containers , batch , series:kubernetes:8

Understanding Jobs and CronJobs

Jobs create one or more Pods to perform a specific task and ensure they successfully complete. CronJobs create Jobs on a schedule.

Jobs

Basic Job Configuration

apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  template:
    spec:
      containers:
      - name: pi
        image: perl:5.34.0
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: Never
  backoffLimit: 4

Job Patterns

1. Non-Parallel Jobs

apiVersion: batch/v1
kind: Job
metadata:
  name: single-task
spec:
  template:
    spec:
      containers:
      - name: worker
        image: busybox
        command: ["echo",  "Single task completed"]
      restartPolicy: Never

2. Parallel Jobs with Fixed Completion Count

apiVersion: batch/v1
kind: Job
metadata:
  name: parallel-fixed
spec:
  completions: 5
  parallelism: 2
  template:
    spec:
      containers:
      - name: worker
        image: busybox
        command: ["echo", "Task completed"]
      restartPolicy: Never

3. Parallel Jobs with Work Queue

apiVersion: batch/v1
kind: Job
metadata:
  name: job-wq
spec:
  parallelism: 2
  template:
    spec:
      containers:
      - name: worker
        image: worker-image
        env:
        - name: REDIS_HOST
          value: redis-service
      restartPolicy: Never

CronJobs

Basic CronJob Configuration

apiVersion: batch/v1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox:1.28
            command:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes cluster
          restartPolicy: OnFailure

Common Use Cases

1. Database Backup

apiVersion: batch/v1
kind: CronJob
metadata:
  name: db-backup
spec:
  schedule: "0 2 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: backup
            image: mysql:8.0
            command:
            - /bin/sh
            - -c
            - mysqldump -h mysql-service -u root -p$MYSQL_ROOT_PASSWORD --all-databases > /backup/dump.sql
            env:
            - name: MYSQL_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mysql-secret
                  key: password
            volumeMounts:
            - name: backup-volume
              mountPath: /backup
          volumes:
          - name: backup-volume
            persistentVolumeClaim:
              claimName: backup-pvc
          restartPolicy: OnFailure

2. Log Rotation

apiVersion: batch/v1
kind: CronJob
metadata:
  name: log-rotation
spec:
  schedule: "0 0 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: log-cleaner
            image: busybox
            command:
            - /bin/sh
            - -c
            - find /var/log -type f -mtime +7 -delete
            volumeMounts:
            - name: log-volume
              mountPath: /var/log
          volumes:
          - name: log-volume
            hostPath:
              path: /var/log
          restartPolicy: OnFailure

Job Control and Management

Job Completion Modes

spec:
  completionMode: Indexed
  completions: 5
  parallelism: 3

TTL Controller for Finished Jobs

spec:
  ttlSecondsAfterFinished: 100

Handling Job Failures

spec:
  backoffLimit: 6
  activeDeadlineSeconds: 600

Best Practices

1. Resource Management

spec:
  template:
    spec:
      containers:
      - name: job-task
        resources:
          requests:
            memory: "64Mi"
            cpu: "250m"
          limits:
            memory: "128Mi"
            cpu: "500m"

2. Pod Security

spec:
  template:
    spec:
      securityContext:
        runAsNonRoot: true
        runAsUser: 1000
      containers:
      - name: job-task
        securityContext:
          allowPrivilegeEscalation: false

3. Error Handling

spec:
  backoffLimit: 4
  template:
    spec:
      containers:
      - name: job-task
        command:
        - /bin/bash
        - -c
        - |
          if ! my-task; then
            echo "Task failed"
            exit 1
          fi

Advanced Configurations

Suspending CronJobs

spec:
  suspend: true

Concurrency Policy

spec:
  concurrencyPolicy: Forbid  # Allow, Forbid, or Replace

Historical Limit

spec:
  successfulJobsHistoryLimit: 3
  failedJobsHistoryLimit: 1

Monitoring and Debugging

Job Status Checking

Terminal window
kubectl get jobs
kubectl get cronjobs
kubectl describe job <job-name>
kubectl logs job/<job-name>

Common Issues

  1. Job Never Completes

    • Check resource constraints
    • Verify logic completion
    • Review logs
    • Check node capacity

  2. CronJob Not Running

    • Verify schedule format
    • Check concurrency policy
    • Review suspend status
    • Check previous job status

Example Scenarios

1. Data Processing Job

apiVersion: batch/v1
kind: Job
metadata:
  name: data-processor
spec:
  parallelism: 3
  completions: 10
  template:
    spec:
      containers:
      - name: processor
        image: data-processor:v1
        env:
        - name: BATCH_SIZE
          value: "1000"
        - name: INPUT_PATH
          value: "/data/input"
        volumeMounts:
        - name: data-volume
          mountPath: /data
      volumes:
      - name: data-volume
        persistentVolumeClaim:
          claimName: data-pvc
      restartPolicy: Never

2. Scheduled Report Generation

apiVersion: batch/v1
kind: CronJob
metadata:
  name: report-generator
spec:
  schedule: "0 6 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: reporter
            image: report-generator:v1
            env:
            - name: REPORT_TYPE
              value: "daily"
            - name: OUTPUT_FORMAT
              value: "pdf"
          restartPolicy: OnFailure

Series Navigation

Conclusion

Jobs and CronJobs are essential for running batch processes and scheduled tasks in Kubernetes. Understanding their configurations and best practices helps in implementing reliable task execution in your cluster.