All my sites went down after upgrading to natty just because one line conf problem … sigh.
All my sites are running php-fpm then nginx, the problem came from these two lines:
fastcgi_param SCRIPT_FILENAME /var/www/xiehang.com/$fastcgi_script_name;
include /etc/nginx/fastcgi_params;
It used to work without problem but obviously the new Ubuntu release changed something in /etc/nginx/fastcgi_params which overwrites previous line.
Swap two lines fixed the problem, but still … 4 hours down time.