I would like to try Xdebug 3.0.0RC1 to explore what has changed and the new features that come with it. I am also using the latest PhpStorm 2020.3 EAP which supports Xdebug 3 with no major config needed. Below is my PhpStorm config for the Debugger:

[![enter image description here](https://i.stack.imgur.com/Xp3hW.png)](https://i.stack.imgur.com/Xp3hW.png)

And here is the configuration I have tried for Xdebug3:

```
zend_extension=/usr/local/lib/php/extensions/no-debug-non-zts-20170718/xdebug.so
xdebug.mode=debug
xdebug.start_with_request=yes
xdebug.client_host=host.docker.internal # here I tried several combinations like: "localhost", "127.0.0.1", "172.17.0.1"
xdebug.client_port=9001 # here I tried several ports 9003 included with no success

```

I have also tried not adding the `client_host/client_port` setting at all and still failing.

I am getting this error:

```
Script php bin/console doctrine:cache:clear-metadata returned with error code 255
!!  [17-Nov-2020 15:24:40 UTC] Xdebug: [Step Debug] Could not connect to debugging client. Tried: host.docker.internal:9001 (through xdebug.client_host/xdebug.client_port) :-(
!!  [17-Nov-2020 15:24:41 UTC] PHP Fatal error:  Method class@anonymous::__toString() must not throw an exception, caught Symfony\Component\DependencyInjection\Exception\AutowiringFailedException:  in /var/www/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Compiler/AutowirePass.php on line 233

```

Some info about my environment:

* Fedora 33
* Docker version 19.03.13, build 4484c46d9d
* PhpStorm 2020.3 EAP Build #PS-203.5784.36

It is curious (because apparently `host.docker.internal` is "not" supported by the Docker version I am using and yet it works) and weird at the same time that the following configuration does work with Xdebug 2 even having the debugger listening for incoming connections all the time:

[![enter image description here](https://i.stack.imgur.com/YrkI6.png)](https://i.stack.imgur.com/YrkI6.png)

```
zend_extension=/usr/local/lib/php/extensions/no-debug-non-zts-20170718/xdebug.so
xdebug.remote_autostart=0
xdebug.remote_enable=1
xdebug.remote_host=host.docker.internal
xdebug.remote_port=9000

```

What I am missing here?

Note: I already applied the solution provided by the Xdebug developer [here](https://stackoverflow.com/a/17259423/719427).