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How to debug remote JVM exposed by ngrok tunnel

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.

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!

Start jmeter distributed testing from clouds

I want to run distributed load testing by jmeter, where servers(linux) are in the cloud and I have ability to start test from my local pc.
Is it even possible or client and servers should be in same subnet?
And in case its possible, may you provide me step by step guide how to achive this goal?
I have tired
https://jmeter.apache.org/usermanual/remote-test.html
https://cloud.google.com/community/tutorials/ssh-port-forwarding-set-up-load-testing-on-compute-engine?hl=ja
but I got error after error.
Before I disabled ssl verification, next error appeared:
error during JRMP connection establishment; nested exception is:
javax.net.ssl.SSLHandshakeException: Remote host terminated the handshake
With disabled ssl verification I have next error:
Error in rconfigure() method java.rmi.MarshalException: error marshalling argume
nts; nested exception is:
java.net.SocketException: Connection reset by peer: socket write error
I have feeligs, like I making smth wrong with setting ip, port or firewall, but cant understand what

It is definitely possible to starts load agents (jmeter-server) from your local system. The only condition is that the traffic should not be blocked by firewall.
Based on your error, it looks like jmeter process is not having permission to open a port, port is already open (although there is a specific exception for this)
You can also try allowing all incoming traffic to your slaves (cloud linux boxes) and try running the test again.

According to the manual you mentioned all you need to do is just to take the following steps:
On your local machine set up the SSH tunnel:
ssh -L 24000:127.0.0.1:24000 -R 25000:127.0.0.1:25000 -L 26000:127.0.0.1:26000 username#hostname_of_cloud_machine
On the cloud machine launch the JMeter slave
./jmeter -s -Jserver.rmi.ssl.disable=true -Jserver_port=24000 -Jserver.rmi.localhostname=127.0.0.1 -Jserver.rmi.localport=26000 -j jmeter.log
Again on the local machine launch the JMeter master:
./jmeter -Jserver.rmi.ssl.disable=true -Jremote_hosts=127.0.0.1:24000 -Jclient.rmi.localport=25000 -Jmode=Statistical -n -t test.jmx -l result.jtl
You don't need to configure any firewalls as all the communication is happening over the SSH tunnel
More information:
Remote hosts and RMI configuration
Apache JMeter Properties Customization Guide

Debug Port in containerized WebLogic server

I have a containerized WebLogic server which is running on my docker host mapped with three port: 5556, 6001, 7001. I have deployed my java product and everything is successful. I have also assaign a debug port on 8453 based on this article on WebLogic:
https://docs.oracle.com/en/cloud/paas/java-cloud/jscug/enable-jvm-debug-port.html#GUID-C83E051D-3A28-4FE7-8333-20F40A06DAEA
In Intellij IDE, I configured my debug port on localhost port 8453 in ‘Edit Configuration…’ . here everything seems extremly OK and good. But as I am going to debug connection gets failed.
"unable to open debugger port (localhost:8453): java.net.connectException "Connection refused: connect"
I am a little bit naive in WebLogic server. It might be because somehow given port not mapped causes this error. Please help me if anybody there had such experience before.

The environmental variable JAVA_OPTIONS is typically being set on startWeblogic.sh. With using a dockerized weblogic, the same variable needs to be set with the debug options and the address.
For example, you can set the variable on your Dockerfile.
The following will set the debug port for the Weblogic applications to 4000 :
ENV JAVA_OPTIONS $JAVA_OPTIONS -Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=4000,server=y,suspend=n
Also this port needs to be exposed.
For example on docker-compose.yml:
ports:
- 4000:4000
On IntelliJ IDEA, the handshake is succesful without using IP Address of the container.

Java Mission Control: Flight Recorder throws: javax.naming.ServiceUnavailableException

I am trying to profile a Java Spring application with the Oracle Java Mission control.
I have the JVM Connection configured as: localhost:7091
and I started the application with java -Dcom.sun.management.jmxremote.rmi.port=7091 -jar app.jar.
When I attempt to start the flight recorder I get an error message.
Failed to retrieve RMIServer stub: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: localhost; nested exception is:
java.net.ConnectException: Connection refused: connect]
Could not connect to a JVM at service:jmx:rmi:///jndi/rmi://localhost:7091/jmxrmi. Make sure one is running and that you are using the correct protocol in the Service URL.
Does anyone know what could be the reason for that error?

You could try to use auto discovery. Then the connection will show up automatically in JMC
-Dcom.sun.management.jmxremote.autodiscovery=true
You can also name the connection so you can identify it easily.
-Dcom.sun.management.jdp.name=App
and disable security
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false

I had this issue. I had installed JDK 10 on Windows Server 2016. With JMC and the JVM I wished to monitor on the same server.
When going live, we switched the IP from a temporary IP to a live IP. However, JMC resolved localhost to the original IP. Also when specifying the server's current IP, JMC resolved it to the original IP.
Adding -Djava.rmi.server.hostname=localhost to the Java process I wanted to monitor, resolved the issue.
However, I will would still be interested to know why JMC (or RMI) still resolves incorrectly.

How do I connect to Derby which is included with WebLogic?

I'm trying to add the Derby included with WebLogic as a data source. I'm running WebLogic 10.3.5. I didn't see a Derby flag in the setDomainEnv.cmd, so I added the client driver to the CLASSPATH:
set CLASSPATH=%PRE_CLASSPATH%;%WEBLOGIC_CLASSPATH%;%POST_CLASSPATH%;%WLP_POST_CLASSPATH%;%WL_HOME%\common\derby\lib\derbyclient.jar
in setDomainEnv.cmd. Now when I try to activate my data source in WebLogic I get:
An error occurred during activation of changes, please see the log for
details. Message icon - Error weblogic.application.ModuleException:
Message icon - Error java.net.ConnectException : Error connecting to
server localhost on port 1527 with message Connection refused:
connect.
What else do I need to do to get this to work?

I believe your local derby is not up yet. To check this, issue:
netstat -an | findstr 1527.
See if it returns anything. If nothing is returned, try to start the Derby Network Service manually. Go to <WLS_HOME>\common\derby\bin and click the startNetworkServer.cmd.
Double check with netstat again. If it's there, you can try to add to the datasource.
Note: this only covers manually start the Derby network service (not automatially start it upon weblogic start, which a bit tricky).

Either whatever is supposed to be running on that port isn't running or there is a firewall issue.