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Welcome back to our series of hands-on introductions to using Cryostat 2.0. This article shows you how to preconfigure custom event templates for Java application monitoring with JDK Flight Recorder (JFR). First, you'll use the new Cryostat Operator and a Red Hat OpenShift ConfigMap to create a custom event template, then you'll instruct the Cryostat Operator to use the ConfigMap when deploying Cryostat. You can use the OpenShift console to interact with Cryostat or edit the YAML file for your Cryostat custom resource. We'll demonstrate both approaches.

Read all of the articles in this series:

Note: Cryostat is JDK Flight Recorder for Kubernetes or Red Hat OpenShift. The Red Hat build of Cryostat 2.0 is now widely available in technology preview. The Red Hat build includes the Cryostat Operator to simplify and automate Cryostat deployment on Red Hat OpenShift.

Create a custom template and ConfigMap

With Cryostat, you can download existing template files directly from a Java virtual machine (JVM). Once you've downloaded a template file to your local machine, you can use the JDK Mission Control (JMC) Template Manager to easily edit the template to suit your needs.

After customizing the template file, it's fairly simple to create a ConfigMap from it. This ConfigMap stores the template file inside of the cluster where Cryostat will run. You can use oc or kubectl in the namespace where Cryostat is to be deployed. Here's the source if you use the former:

$ oc create configmap my-template --from-file=/path/to/custom.jfc

This command creates a ConfigMap named my-template from a file on your local machine, located at /path/to/custom.jfc. The file will be placed inside the ConfigMap under the custom.jfc filename.

Add your ConfigMap to the Cryostat Operator

Once you've created a ConfigMap, you only need to instruct the Cryostat Operator to use it when deploying Cryostat. You can do this when you create a Cryostat custom resource, or by updating an existing one. If you're installing Cryostat using the OpenShift console, select Event Templates under the Cryostat custom resource that you want to update. Choose Add Event Template. The Config Map Name drop-down list will display all ConfigMaps in the local namespace. Select the ConfigMap containing the event template you just created. For Filename, enter the name of the .jfc file within the ConfigMap. In Figure 1, we're using custom.jfc, which we created in the previous section.

Creating an OpenShift ConfigMap containing a JDK .jfc event template definition file.
Figure 1. Create a ConfigMap with a JDK .jfc event template definition file.

You can also work directly with the YAML for the Cryostat custom resource. The process is similar to what you did in the console. Add an eventTemplates property to the spec section, if one isn't already present. Then, add an array entry with configMapName referencing the name of the ConfigMap, and a filename referencing the filename within the ConfigMap. The YAML below mirrors what we did in the OpenShift console example in Figure 1.

apiVersion: operator.cryostat.io/v1beta1

kind: Cryostat


  name: cryostat-sample



  - configMapName: custom-template

    filename: my-template.jfc

Once you've saved your changes to the Cryostat custom resource, the Cryostat Operator will deploy Cryostat with this template preconfigured. Visiting the Cryostat web application will show that the template is present and available to use for creating new JDK flight recordings, as you can see in Figure 2.

The Event Template list displays the template created via ConfigMap.
Figure 2. The Event Template list displays the template created via ConfigMap.


In this article, you've learned how to preconfigure Cryostat with customized event templates using OpenShift ConfigMaps. You can use customized templates to gather the specific data you need in your JDK flight recordings. Visit Cryostat.io and see the other articles in this series for further details:

Last updated: September 20, 2023