I have tried this four times in the past 30 minutes:
 
http://cocoon.zones.apache.org/demos/trunk/
 
returns
 

502 Bad Gateway

The upstream server is not responding.

If you're trying to access a live Cocoon demo, it might be currently restarting, as it does twice a day. This takes some time as the demo is upgraded from our Subversion repository, and completely rebuilt.

Please check back in 10 minutes, or inform dev (at) cocoon.apache.org if the problem persists.

 

Hope this is helpful.

 
 
Robin