After chef installed nginx, it failed to start it :
STDERR: nginx: [emerg] getpwnam("www-data") failed in /etc/nginx/nginx.conf:1
nginx: configuration file /etc/nginx/nginx.conf test failed
After investigation, I found that the default user is nginx and not www-data like in the conf file created by chef with the default nginx user from attributes.
vagrant@ci ~ $ cat /etc/passwd | grep www
vagrant@ci ~ $ cat /etc/passwd | grep nginx
nginx:x:105:241:added by portage for nginx:/var/lib/nginx:/sbin/nologin
vagrant@ci ~ $