Adding websites to nginx without restarting nginx

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http://serverfault.com – There are many companies that load a web application for you on their servers like say wordpress etc., and since they have other customers on the same server I was curious how they do this w/o having to restart the web server? If they do restart the web server, it would take down other client sites and that wouldn't be a good situation to be in. Is it possible with nginx? (HowTos)