How can I debug my Quarkus application that is running in dev mode?

In case you are using IntellJ IDEA run your application normally (without debugging) and then go to

RUN --> Attach to Process.

This will attach the debugger separately and has worked for me.

When launching a Quarkus app simply using mvn quarkus:dev, the running application is configured to open port 5005 for remote debugging. That means that all you have to do is point your remote debugger to that port and you will be able to debug it in your favorite IDE/lightweight editor.

If however you would like to be able to suspend the application until a debugger is connected then simply execute:

mvn quarkus:dev -Dsuspend

The same port is used (5005) but this time the application doesn't start until a remote debugger is connected. You can use -Ddebug to change the debugging port.

UPDATE

As of version 2020.3, IntelliJ Ultimate should recognize a quarkus application and automatically create a launch configuration that uses quarkus:dev under the hood.