If you set an application to use more file descriptors than ulimit -n returns, then either the application will be smart and fix its configuration by using MAX(configured limit, ulimit -n) or it'll start dropping requests because it's assuming it's allowed to open more file descriptors.
Increasing an application's maximum file descriptors past ulimit -n is bad advice. The proper way is to increase the limit in /etc/security/limits.conf (note that assigning a limit to * applies it to every user but root, so if you really want to assign a limit to every user, you must assign it to both * and root) and then increase the application's max file descriptors. Restarting the application is usually required, although on newer versions of Linux, changing limits for running processes is possible.
Increasing an application's maximum file descriptors past ulimit -n is bad advice. The proper way is to increase the limit in /etc/security/limits.conf (note that assigning a limit to * applies it to every user but root, so if you really want to assign a limit to every user, you must assign it to both * and root) and then increase the application's max file descriptors. Restarting the application is usually required, although on newer versions of Linux, changing limits for running processes is possible.