How to debug remote JVM exposed by ngrok tunnel

Question

I have a java process on one of my machines listening on port 4502. I have created a tunnel using ngrok so that I can access the application on my development machine. The issue I'm facing is attaching a debugger to the remote JVM.

Here is the debug java configuration I'm using:

-agentlib:jdwp=transport=dt_socket,address=*:5005,server=y,suspend=n

Here is the ngrok configuration for the tunnel to the application:

ngrok http 4502

Here is the ngrok configuration for the tunnel to the JVM (I have also tried http protocol with no luck):

ngrok tcp 5005

ngrok outputs the following for the tcp tunnel:

Forwarding tcp://2.tcp.eu.ngrok.io:10928 -> 127.0.0.1:5005

Using IntelliJ, I configure the remote debugging like this:

Debugger mode: Attach to remote JVM
Host: tcp://2.tcp.eu.ngrok.io
Port: 10928

I get the following error when starting the debugger:

Error running 'Debug Author Desktop': Unable to open debugger port (tcp://2.tcp.eu.ngrok.io:10928): java.io.IOException "handshake failed - connection prematurally closed"

On the machine running the java process, I have made sure that the 5005 port is open before starting the process. On the machine using IntelliJ, I have made sure that the 10928 port is open. What must I do so that I can attach the debugger to the process running on my second machine? Any help would be appreciated.

Answer 1

I've found the solution. The issue was in the Remote Debugger configuration. When specifying the host, you must not include the protocol. Once I changed tcp://2.tcp.eu.ngrok.io to 2.tcp.eu.ngrok.io , it worked!