WSL2 port forwarding is not working if accessed from java

[vigneshr6]

Environment

Windows 10 Home

Windows build number: [Version 10.0.19042.630]
Your Distribution version: [Ubuntu 18.04]
Whether the issue is on WSL 2 and/or WSL 1: [WSL 2]

Steps to reproduce

1. Start a webserver in WSL2 ubuntu 18.04
2. Access the webserver from a java HTTP client application from windows.

WSL logs:

Expected behavior

WSL webserver should be accessible with localhost from java application.

Actual behavior

could not connect the webserver with localhost. But I could connect with private IP from the same java application. Powershell Invoke-WebRequest command can also work with localhost.

[hb020]

See #4150
This has been discussed often, and MS does not seem to care about it. This behaviour is as designed.
My suggestion: go back to WSL or set up a real VM.

[therealkenc]

10.0.19042.630

Likely #4851 with a side of #5298, like #5706 (message), others.

Moving over to discussion (similar #6240) for work-arounds to the specific use-case since there isn't a novel actionable.

[wendersonsouza]

I got the same issue trying to access a jasperreport server hosted by wsl .
got connection refused attempting to connect the server from a java application using wsl2.
lead by this tutorial I set up to wsl1 and then worked well so far.
https://www.tenforums.com/tutorials/164318-how-set-linux-distribution-version-wsl-1-wsl-2-windows-10-a.html

[albertopiva-tv]

This issue occurred to me today: a spring boot app launched from WSL2 was not reachable by another spring boot app launched from outside WSL when using PC hostname or localhost. I had to use IP address, but it's not really convenient, it could change.
The issue happens the other way around also, a java app launched from windows is not reachable from WSL using hostname or localhost

[michaldo]

In my case connection from Win to WSL2 by Java process depends on property java.net.preferIPv6Addresses

Connection works for values system and true but does not work for false and when missing, because false is default

See https://stackoverflow.com/a/71967275 for details

[marcoblos]

After hours trying to figure out possible problems between WSL2 + Windows + Firewall, etc, @michaldo answer was the only one that worked here... Instead of running my application like: mvn quarkus:dev , I ran it like this: mvn quarkus:dev -Djava.net.preferIPv6Addresses=true.

[namedgraph]

This is what helped me to connect VisualVM on Win10 over JMX to a Docker container running on WSL2: https://stackoverflow.com/a/71881475/1003113