Helm chart for Kubernetes Cronjob

One CronJob object is like one line of a crontab (cron table) file. It runs a job periodically on a given schedule, written in Cron format. Cron jobs are useful for creating periodic and recurring tasks, like running backups or sending emails. Cron jobs can also schedule individual tasks for a specific time, such as if you want to schedule a job for a low activity period.

You can download the chart folder from repo: https://github.com/cloudops-guru/helm-cronjob

Standard Helm template to create a Kubernetes CronJob

Here the helm chart to write your first cronjob.yaml using helm : In this example we are configuring single cronjob that executes a script “/opt/myapp/myscript.sh” on every day at 10:30. The script require some the secrets and keys which is already saved to kube secret “myapp-secret” and we are injecting these values using env variables in container.

CronJob.yaml

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  namespace: {{ .Values.env }}
  name: {{ .Chart.Name }}
  labels:
    draft: {{ default "draft-app" .Values.draft }}
    chart: "{{ .Chart.Name }}-{{ .Chart.Version | replace "+" "_" }}"
spec:
  schedule: {{ .Values.schedule }}
  successfulJobsHistoryLimit: 0 
  jobTemplate:
    spec:
      template:
        metadata:
          labels:
            draft: {{ default "draft-app" .Values.draft }}
            app: {{ .Chart.Name }} 
        spec:       
          containers:
          - name: {{ .Chart.Name }}
            image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
            imagePullPolicy: {{ .Values.image.pullPolicy }} 
            args:
              - sh
              - -c
              - |
                sleep 2 
                "/opt/myapp/myscript.sh"
                sleep 30
            env: 
              - name: APP_SECRET
                valueFrom:
                  secretKeyRef:
                    name: {{ .Values.appsecret }}
                    key: app_secret
              - name: APP_CLIENT_ID
                valueFrom:
                  secretKeyRef:
                    name: {{ .Values.appsecret }}
                    key: app_client_id 
            ports:
            - containerPort: {{ .Values.service.internalPort }} 
          restartPolicy: {{ .Values.restartPolicy }}
          imagePullSecrets:
            - name: artifactory

Values.yaml

env: dev
appsecret: myapp-secret 
schedule: '"30 10 * * *"'
restartPolicy: OnFailure
image:
  repository: XYZ
  tag: 1.0.2
  pullPolicy: IfNotPresent 
service: 
  internalPort: 8028

Iterate multiple Jobs in helm chart CronJob

We can use the ‘range’ instruction for iterative cronjob resource, using the values.yaml you could be able to pass multiple values for all different jobs. In the range instruction, you need to call all Values $.Values.val instead of .Values.val . You need to have and — and end to close the loop.

CronJob.yaml

{{- range $job, $val := .Values.cronjob.crons }}
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  namespace: {{ .Values.env }}
  name: {{ .name }}
  labels:
    draft: {{ default "draft-app" $.Values.draft }}
    chart: "{{ .Chart.Name }}-{{ .Chart.Version | replace "+" "_" }}"
spec:
  schedule: {{ .schedule | quote }}
  successfulJobsHistoryLimit: 0 
  jobTemplate:
    spec:
      template:
        metadata:
          labels:
            draft: {{ default "draft-app" $.Values.draft }}
            app: {{ .name }}
        spec:       
          containers:
          - name: {{ .name }}
            image: "{{ $.Values.image.repository }}:{{ $.Values.image.tag }}"
            imagePullPolicy: {{ $.Values.image.pullPolicy }} 
            args:
              - sh
              - -c
              - |
                sleep 2 
                "./bin/console --env={{ $.Values.env }} {{ .command}}"
                sleep 30 
            ports:
            - containerPort: {{ $.Values.service.internalPort }} 
          restartPolicy: {{ $.Values.restartPolicy }}
          imagePullSecrets:
            - name: artifactory 
---
{{- end}}

Values.yaml

env: dev  
restartPolicy: OnFailure
image:
  repository: XYZ
  tag: 1.0.2
  pullPolicy: IfNotPresent 
service: 
  internalPort: 8028  
crons:
 "0":
 name: cog-first-cron
 command: /opt/myapp/myscript1.sh
 schedule: "10 4 * * *"
 "1":
 name: cog-second-cron
 command: /opt/myapp/myscript2.sh
 schedule: "" 30 5 * * *" 
 "2":
 name: cog-third-cron
 command: /opt/myapp/myscript3.sh
 schedule: "0/5 * * * *"

https://cloudops-guru.in/2020/09/17/helm-chart-define-multiple-cronjob/