Kubernetes for Java Developers - Debug Application

Debug application

At this point, we deployed our application within a local cluster. But now we have a problem. How do I debug my application that is inside the docker that is inside the kubernetes that is inside a virtual machine?

Prepare to debug

In this case, we will use a remote Java debug.

First step:

Prepare your Dockerfile:

FROM openjdk:11.0.3-jdk-slim
RUN mkdir /usr/myapp
COPY target/java-kubernetes.jar /usr/myapp/app.jar
WORKDIR /usr/myapp
EXPOSE 8080
ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -jar app.jar" ]

This ENTRYPOINT allows you to pass options to the java through $JAVA_OPTS environment variable.

Second step:

Changing app-configmap.yaml file to fill $JAVA_OPTS.

JAVA_OPTS: "-agentlib:jdwp=transport=dt_socket,address=*:5005,server=y,suspend=n -Xms256m -Xmx512m -XX:MaxMetaspaceSize=128m"

Third step:

Building and deploy app:

mvn clean install
eval $(minikube -p dev.to docker-env) && docker build --force-rm -t java-k8s .
kubectl apply -f kubernetes/app/

Fourth step:

Exposing debug port to localhost:

Get pods:

kubectl get pods -n dev-to

NAME                     READY   STATUS    RESTARTS   AGE
myapp-7796bc89bf-h2f82   1/1     Running   0          3h3m

Expose pod 5005 port:

kubectl port-forward -n dev-to myapp-7796bc89bf-h2f82 5005:5005
Forwarding from 127.0.0.1:5005 -> 5005
Forwarding from [::1]:5005 -> 5005

Change your pod name as necessary.

Create a remote debug on your IDE:

On IntelliJ, go to Run/Debug Configurations.

• Add new remote configuration like this:

After that, run the configuration. You should see the message below:

Connected to the target VM, address: 'localhost:5005', transport: 'socket'

Check if works:

Now, you can set a breakpoint in the HelloController.

minikube -p dev.to service -n dev-to myapp --url
http://192.168.99.100:32301

curl http://192.168.99.100:32301/hello

Conclusion

In this part, we learned about how to debug application inside a local kubernetes cluster.

In the next part, we will see some good practices and how to access application with friendly URL using Ingress.

See you soon!