This module, in particular, brings much more functionality to Nginx than a simple set of directives. It defines a whole new level of request processing that will be explained throughout this section.

Initially, the purpose of this module (as the name suggests) is to perform URL rewriting. This mechanism allows you to get rid of ugly URLs containing multiple parameters, for instance, http://example.com/article.php?id=1234&comment=32—such URLs being particularly uninformative and meaningless for a regular visitor.

Instead, links to your website will contain useful information that indicates the nature of the page you are about to visit. The URL given in the example becomes http://website.com/article-1234-32-US-economy-strengthens.html. This solution is not only more interesting for your visitors, but also for search engines. URL rewriting is a key element to Search Engine Optimization (SEO).

The principle behind this mechanism is simple: it consists of rewriting the URI of the client request after it is received, before serving the file. Once rewritten, the URI is matched against location blocks in order to find the configuration that should be applied to the request. The technique is further detailed in the coming sections.