cronjob-runner

README

cronjob-runner

This is a command to run a Job from CronJob in Kubernetes. It is designed for running a one-shot job by a job infrastructure such as GitHub Actions or Jenkins.

Getting Started

To run a Job from the CronJob,

cronjob-runner [--namespace your-namespace] --cronjob-name your-cronjob-name

Here is an example output of simple CronJob.

$ cronjob-runner --cronjob-name simple
04:03:14.740975 main.go:41: Cluster version v1.27.3
04:03:14.744844 create.go:27: Found the CronJob default/simple
04:03:14.751085 create.go:47: Created a Job default/simple-xv2g4
apiVersion: batch/v1
kind: Job
metadata:
  annotations:
    batch.kubernetes.io/job-tracking: ""
  creationTimestamp: "2023-10-31T04:03:14Z"
  generateName: simple-
  generation: 1
  labels:
    batch.kubernetes.io/controller-uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
    batch.kubernetes.io/job-name: simple-xv2g4
    controller-uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
    job-name: simple-xv2g4
  name: simple-xv2g4
  namespace: default
  ownerReferences:
  - apiVersion: batch/v1
    controller: true
    kind: CronJob
    name: simple
    uid: 245bc058-c6f4-406b-91e5-f2bb70481d4d
  resourceVersion: "312"
  uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
spec:
  backoffLimit: 3
  completionMode: NonIndexed
  completions: 1
  parallelism: 1
  selector:
    matchLabels:
      batch.kubernetes.io/controller-uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
  suspend: false
  template:
    metadata:
      creationTimestamp: null
      labels:
        batch.kubernetes.io/controller-uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
        batch.kubernetes.io/job-name: simple-xv2g4
        controller-uid: d36873c5-e4e2-49ae-9f95-ce8c4858974f
        job-name: simple-xv2g4
    spec:
      containers:
      - command:
        - bash
        - -c
        - |
          set -eux
          echo "Hello, world!"
          date
          uname -a
          exit 0
        image: debian:stable
        imagePullPolicy: IfNotPresent
        name: example
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Never
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
status: {}
04:03:14.751671 informer.go:41: Watching a pod of job default/simple-xv2g4
04:03:14.751708 informer.go:36: Watching the job default/simple-xv2g4
04:03:14.756822 informer.go:47: Job default/simple-xv2g4 is created
04:03:27.590782 informer.go:51: Pod default/simple-xv2g4-gtrv4 is Pending
04:03:34.989551 informer.go:68: Pod default/simple-xv2g4-gtrv4 is Running
04:03:34.989577 informer.go:81: Pod default/simple-xv2g4-gtrv4: Container example is running
04:03:34.989589 tail.go:18: Following the container log of default/simple-xv2g4-gtrv4/example
2023-10-31T04:03:34.032032575Z | default/simple-xv2g4-gtrv4/example | + echo 'Hello, world!'
2023-10-31T04:03:34.032057675Z | default/simple-xv2g4-gtrv4/example | + date
2023-10-31T04:03:34.032061375Z | default/simple-xv2g4-gtrv4/example | + uname -a
2023-10-31T04:03:34.032064275Z | default/simple-xv2g4-gtrv4/example | + exit 0
2023-10-31T04:03:34.032045275Z | default/simple-xv2g4-gtrv4/example | Hello, world!
2023-10-31T04:03:34.032071875Z | default/simple-xv2g4-gtrv4/example | Tue Oct 31 04:03:34 UTC 2023
2023-10-31T04:03:34.032075775Z | default/simple-xv2g4-gtrv4/example | Linux simple-xv2g4-gtrv4 6.2.0-1015-azure #15~22.04.1-Ubuntu SMP Fri Oct  6 13:20:44 UTC 2023 x86_64 GNU/Linux
04:03:35.754953 informer.go:85: Pod default/simple-xv2g4-gtrv4: Container example is terminated with exit code 0 (Completed)
04:03:36.840624 informer.go:68: Pod default/simple-xv2g4-gtrv4 is Succeeded
04:03:37.854908 informer.go:56: Job default/simple-xv2g4 is Complete 
04:03:37.855034 main.go:53: Stopped background workers

This command create a Job from the job template of CronJob. It shows the status of Job, Pods and containers. It follows the log streams of all containers.

Inject environment variables

To inject environment variables to all containers,

cronjob-runner [--namespace your-namespace] --cronjob-name your-cronjob-name --env KEY=VALUE

For example,

$ cronjob-runner --cronjob-name CreateItem --env ITEM_NAME=example --env ITEM_PRICE=100

Do not inject any secret, because anyone can see it by the log or kubectl command.

Design

Owner references

This command sets the owner reference of a Job to the parent CronJob. Here is the relationship of resources.

graph LR
  CronJob --> Job --> Pod

When a Job is completed or failed, the old Job will be cleaned up by CronJob controller. See Jobs section of the official document for details.

Less runtime injection

For IaC and GitOps principal, every resource should be managed as code. This command does not allow any modification of the job template, except the environment variables.