Enable Debug Component in Symfony 2.3 - debugging

Question

Before opening a ticket in the symfony repository, I just wanted to check if I have missed something obvious.
I want to enable the debug component (for having these nice exception screens, etc..).
I just installed symfony using
composer create-project symfony/framework-standard-edition symfony 2.3.1
For testing purposes I added an exception to the WelcomeController:
class WelcomeController extends Controller
{
public function indexAction()
{
throw new \Exception("test");
/*
* The action's view can be rendered using render() method
* or #Template annotation as demonstrated in DemoController.
*
*/
return $this->render('AcmeDemoBundle:Welcome:index.html.twig');
}
}
Instead of showing me the (old) exception screen, I am just getting a 502 Bad Gateway from nginx.
app_dev.php:
//$loader = require_once __DIR__.'/../app/bootstrap.php.cache';
$loader = require_once __DIR__.'/../app/autoload.php';
Debug::enable(-1);
require_once __DIR__.'/../app/AppKernel.php';
$kernel = new AppKernel('dev', true);
//$kernel->loadClassCache();
Request::enableHttpMethodParameterOverride();
$request = Request::createFromGlobals();
$response = $kernel->handle($request);
$response->send();
$kernel->terminate($request, $response);
Update:
Handling PHP errors does work however:
IDoNotExist();
produces the gray symfony error screen.

Answer 1

Ok, the problem was an error in the nginx config.
The error log of nginx revealed the following:
2013/07/03 14:33:05 [error] 22792#0: *15 upstream sent too big header while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET /test/symfony_2.3.1/web/app_dev.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9111", host: "localhost"
I fixed it with adding
fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;
for the server {} in the nginx config (for reference http://forum.nginx.org/read.php?2,188352).
This first occured with 2.3.0, 2.2.3 works without this fix.
Ticket related to this issue: https://github.com/symfony/symfony/issues/8413