cronjob-runner

cronjob-runner

This is a command line tool to run a Job from CronJob template in Kubernetes. It tails the container logs.

Getting Started

Prerequisites

Download the latest release from:

• GitHub Releases
• go install github.com/int128/cronjob-runner@latest

Create a CronJob into the cluster.

For a one-shot job, you need to set suspend field of CronJob to prevent scheduling. Here is an example.

apiVersion: batch/v1
kind: CronJob
spec:
  # NOTE: This is a one-shot job for cronjob-runner. Do not enable scheduling.
  suspend: true
  schedule: '@annually'
  jobTemplate:
    spec: # ...snip...

Run a Job

To run a Job from the CronJob template,

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

When the Job status is succeeded, this command exits with code 0. Otherwise, it exits with code 1.

Here is an example output of a simple CronJob.

$ cronjob-runner --cronjob-name simple
05:29:09.163225 main.go:34: INFO Found the CronJob cronJob.namespace=default cronJob.name=simple
05:29:09.168399 create.go:46: INFO Created a Job job.namespace=default job.name=simple-vww6r
...
05:29:09.169854 informer.go:46: INFO Watching Pod job.namespace=default job.name=simple-vww6r
05:29:09.169929 informer.go:39: INFO Watching Job job.namespace=default job.name=simple-vww6r
05:29:09.173155 informer.go:53: INFO Job is found job.namespace=default job.name=simple-vww6r
05:29:21.371217 informer.go:68: INFO Pod is created pod.namespace=default pod.name=simple-vww6r-v876l pod.phase=Pending
05:29:21.376853 informer.go:125: INFO Pod is not scheduled pod.namespace=default pod.name=simple-vww6r-v876l reason=Unschedulable message="0/1 nodes are available: 1 node(s) had untolerated taint {node.kubernetes.io/not-ready: }. preemption: 0/1 nodes are available: 1 Preemption is not helpful for scheduling."
05:29:23.329947 informer.go:122: INFO Pod is scheduled pod.namespace=default pod.name=simple-vww6r-v876l node=kind-control-plane
05:29:26.862470 informer.go:99: INFO Pod is running pod.namespace=default pod.name=simple-vww6r-v876l pod.phase=Running
05:29:26.862496 informer.go:181: INFO Container is running pod.namespace=default pod.name=simple-vww6r-v876l container.name=example
05:29:26.862529 tail.go:49: INFO Tailing the container log pod.namespace=default pod.name=simple-vww6r-v876l container.name=example
+ echo 'Hello, world!'
+ date
Hello, world!
Sat Mar 23 05:29:26 UTC 2024
+ uname -a
Linux simple-vww6r-v876l 6.5.0-1016-azure #16~22.04.1-Ubuntu SMP Fri Feb 16 15:42:02 UTC 2024 x86_64 GNU/Linux
+ exit 0
05:29:27.798466 informer.go:184: INFO Container is terminated pod.namespace=default pod.name=simple-vww6r-v876l container.name=example exitCode=0 reason=Completed message=""
05:29:28.885837 informer.go:101: INFO Pod is succeeded pod.namespace=default pod.name=simple-vww6r-v876l pod.phase=Succeeded
05:29:29.895247 informer.go:81: INFO Job is completed job.namespace=default job.name=simple-vww6r
05:29:29.895645 run.go:85: INFO Stopped background workers

See also the e2e-test workflow runs.

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 create-item --env ITEM_NAME=example --env ITEM_PRICE=100

⚠ Do not inject any secret. Anyone can see it by kubectl get or kubectl logs.

Design

How it works

This command runs a Job as follows:

1. Get the CronJob resource.
2. Create a Job resource from the job template of CronJob.
3. When the status of Job, Pod or container is changed, show the status.
4. When a container is started, tail the stream of container logs.

Owner references

This command sets an owner reference from a Job to the parent CronJob. For example,

    ownerReferences:
    - apiVersion: batch/v1
      controller: true
      kind: CronJob
      name: simple
      uid: 948027a3-60af-41d2-8752-6a3be860a200

When a Job is completed or failed, CronJob controller will clean up the outdated Jobs if spec.successfulJobsHistoryLimit or spec.failedJobsHistoryLimit is set. See CronJob section of the official document for details.

Here is the relationship of Kubernetes resources.

graph LR
  subgraph CronJob
    JobTemplate
  end
  JobTemplate --> Job
  subgraph Job
    PodTemplate
  end
  PodTemplate --> Pod
  subgraph Pod
    Container
  end