Debugging Java Applications On OpenShift and Kubernetes

As a follow on to my previous post, I thought it would be interesting to describe how to live debug a Java application running on OpenShift.

Setup

sudo oc cluster up --version=latest  # Any OpenShift environment will work

oc login # as developer:developer

oc new-app openshift/wildfly-101-centos7~https://github.com/danmcp/openshift-jee-sample.git

oc expose service/openshift-jee-sample

oc set env dc/openshift-jee-sample DEBUG=true # Enable the debug port


Next, browse to the web console and log in as developer:developer. Select My Project and click on the url for openshift-jee-sample in the upper right. You should see the index.html page. Add /HelloWorld to the end of the url and you should see the output of the HelloWorld Servlet.

You'll need to use port forwarding to expose the debug port from the container to a local port on your host. Using port forwarding is ideal because it keeps you from having to expose the container debug port to the rest of the cluster.

oc get pods  # To get the name of the running pod you will sync to

oc port-forward <pod_name> 8787:8787 # Replace <pod_name> with the value from the previous step


I'm going to use Eclipse for my example, but you can use any IDE or CLI (such as jdb) that supports remote debugging. If you are using Eclipse, you'll want to download the source and add it to your workspace.

git clone https://github.com/danmcp/openshift-jee-sample.git

Demo

At this point, you're all set to connect your debugger and start stepping through some code:

[video width="1920" height="1080" webm="https://blog.openshift.com/wp-content/uploads/java_debug.webm"][/video]

Wrap Up

My example was with oc cluster up but the basic steps of setting DEBUG=true and oc port-forward will work with any OpenShift environment and with all of our JBoss images. Happy debugging!