Varnish is a web application accelerator tool, which has been gaining a lot in popularity in recent years, as it can increase the speed of any website, at times even by 100 percent, depending on the content. This tool is occasionally referred to as a caching HTTP reverse proxy too and is used to lower the overall load on the physical machine and to improve the access speed for the site visitors. Every time a visitor loads a page on a certain Internet site, the browser request is taken care of by the web server and the requested info is returned as a response. If the Varnish accelerator is activated, it caches the web pages that the visitor opens and if any of them is loaded again, it is delivered by Varnish and not by the web server directly. The increase in the performance comes from the fact that the accelerator processes the web requests considerably faster than any web server, which leads to much faster browsing speeds for the visitors. If any data is updated in the meantime, the cached pages will also be ‘refreshed’ the next time someone opens them.