How did nginx resolve names?

[basti]

Hello,

first of all, I'm not sure if it is a php or nginx problem.

Today I had the problem, that nginx run into "504 Gateway Time-out" when 
the first nameserver in /etc/resolv.conf did not answer.

The php application is query some names (db-server for example).

Did nginx use nsswitch?
Did someone know how php resolve the names?

If the first dns server answer nxdomain it's OK.
But if the first one did *not* answer / get timeout it should ask the 
second one.

Best Regards,