A logo showing the text blog.marcnuri.com
Español
Home»Java»Trigger Kubernetes CronJob manually from Java using YAKC

Recent Posts

  • Fabric8 Kubernetes Client 7.2 is now available!
  • Connecting to an MCP Server from JavaScript using AI SDK
  • Connecting to an MCP Server from JavaScript using LangChain.js
  • The Future of Developer Tools: Adapting to Machine-Based Developers
  • Connecting to a Model Context Protocol (MCP) Server from Java using LangChain4j

Categories

  • Artificial Intelligence
  • Front-end
  • Go
  • Industry and business
  • Java
  • JavaScript
  • Legacy
  • Operations
  • Personal
  • Pet projects
  • Tools

Archives

  • May 2025
  • April 2025
  • March 2025
  • February 2025
  • January 2025
  • December 2024
  • November 2024
  • August 2024
  • June 2024
  • May 2024
  • April 2024
  • March 2024
  • February 2024
  • January 2024
  • December 2023
  • November 2023
  • October 2023
  • September 2023
  • August 2023
  • July 2023
  • June 2023
  • May 2023
  • April 2023
  • March 2023
  • February 2023
  • January 2023
  • December 2022
  • November 2022
  • October 2022
  • September 2022
  • August 2022
  • July 2022
  • June 2022
  • May 2022
  • March 2022
  • February 2022
  • January 2022
  • December 2021
  • November 2021
  • October 2021
  • September 2021
  • August 2021
  • July 2021
  • January 2021
  • December 2020
  • November 2020
  • October 2020
  • September 2020
  • August 2020
  • July 2020
  • June 2020
  • May 2020
  • February 2020
  • January 2020
  • December 2019
  • October 2019
  • September 2019
  • July 2019
  • March 2019
  • November 2018
  • July 2018
  • June 2018
  • May 2018
  • April 2018
  • March 2018
  • February 2018
  • December 2017
  • July 2017
  • January 2017
  • December 2015
  • November 2015
  • December 2014
  • March 2014
  • February 2011
  • November 2008
  • June 2008
  • May 2008
  • April 2008
  • January 2008
  • November 2007
  • September 2007
  • August 2007
  • July 2007
  • June 2007
  • May 2007
  • April 2007
  • March 2007

Trigger Kubernetes CronJob manually from Java using YAKC

2021-01-04 in Java tagged Java / JBang / DevOps / Kubernetes / REST / YAKC by Marc Nuri | Last updated: 2021-06-05

Introduction

In this post, I’ll show you how to perform the equivalent to kubectl --from=cronjob/<cronjob-name> <job-name> (manual trigger) from Java using YAKC- Yet Another Kubernetes Client.

This performs something similar to what the official Kubernetes Dashboard CronJob trigger action does.

A screenshot of Kubernetes Dashboard: Trigger CronJob manually
A screenshot of Kubernetes Dashboard: Trigger CronJob manually

CronJob manual trigger

Once you’ve deployed a CronJob to your cluster, in most cases it makes sense to trigger a test run. You probably need to check that everything works fine without having to wait for the scheduled time.

Starting at version 1.10, Kubernetes offers a way to create a Job from a CronJob using kubectl. This basically translates into manually triggering the CronJob.

Following is the code implementation in Kubectl:

1func (o *CreateJobOptions) createJobFromCronJob(cronJob *batchv1beta1.CronJob) *batchv1.Job {
2  annotations := make(map[string]string)
3  annotations["cronjob.kubernetes.io/instantiate"] = "manual"
4  for k, v := range cronJob.Spec.JobTemplate.Annotations {
5    annotations[k] = v
6  }
7
8  job := &batchv1.Job{
9    // this is ok because we know exactly how we want to be serialized
10    TypeMeta: metav1.TypeMeta{APIVersion: batchv1.SchemeGroupVersion.String(), Kind: "Job"},
11    ObjectMeta: metav1.ObjectMeta{
12      Name:        o.Name,
13      Annotations: annotations,
14      Labels:      cronJob.Spec.JobTemplate.Labels,
15      OwnerReferences: []metav1.OwnerReference{
16        {
17          APIVersion: batchv1beta1.SchemeGroupVersion.String(),
18          Kind:       cronJob.Kind,
19          Name:       cronJob.GetName(),
20          UID:        cronJob.GetUID(),
21        },
22      },
23    },
24    Spec: cronJob.Spec.JobTemplate.Spec,
25  }
26  if o.EnforceNamespace {
27    job.Namespace = o.Namespace
28  }
29  return job
30}

In the previous code snippet, we see how kubectl creates a new Job using the CronJob’s JobTemplate and propagates the labels.

Trigger CronJob from Java

Now that we’ve seen how kubectl creates a Job from a CronJob, let’s see how we can achieve this with YAKC.

1final CronJob cronJob = kc.create(BatchV1beta1Api.class).readNamespacedCronJob(name, applicableNamespace).get();
2final String jobName = String.format("%s-manual-%s",
3  name.length() > 38 ? name.substring(0, 38) : name,
4  new Random().nextInt(999999)
5);
6kc.create(BatchV1Api.class).createNamespacedJob(applicableNamespace, Job.builder()
7  .metadata(ObjectMeta.builder()
8    .name(jobName).namespace(applicableNamespace)
9    .labels(new HashMap<>(Optional.ofNullable(cronJob.getMetadata().getLabels()).orElse(Collections.emptyMap())))
10    .putInAnnotations("cronjob.kubernetes.io/instantiate", "manual")
11    .addToOwnerReferences(OwnerReference.builder()
12      .kind(cronJob.getKind())
13      .apiVersion(cronJob.getApiVersion())
14      .controller(false)
15      .name(cronJob.getMetadata().getName())
16      .uid(cronJob.getMetadata().getUid())
17      .build())
18    .build())
19  .spec(cronJob.getSpec().getJobTemplate().getSpec())

The previous code snippet is part of the CronJobs jbang quickstart.

The first step is to retrieve the actual CronJob from the cluster. Next, we generate a random name for the manually triggered job using the CronJob’s name as the prefix.

Finally, we create a new Job using the retrieved CronJob’s JobTemplateSpec and propagate its labels. We also add an owner reference to the created Job so that it can be associated and listed when querying the CronJob.

Since this example is hosted as a jbang script, you can test it by running the following command:

1jbang https://github.com/manusa/yakc/blob/master/quickstarts/jbang/CronJobs.java trigger $cronJobName

Following you can check the operation result in YAKC – Kubernetes Dashboard interface (you can read more about this project here):

YAKC Kubernetes Dashboard CronJob manual trigger demo
YAKC Kubernetes Dashboard CronJob manual trigger demo

Conclusion

In this post, I’ve shown you how to manually trigger CronJobs from Java using YAKC.

I’ve extracted the code for this post from the jbang quickstart section of YAKC. You can learn more by visiting YAKC’s GitHub project site. You can also see related code here.

Twitter iconFacebook iconLinkedIn iconPinterest iconEmail icon

Post navigation
Quarkus 2 + Kubernetes Maven Plugin + GraalVM integrationYAKC – Kubernetes Dashboard
© 2007 - 2025 Marc Nuri