Page Speed is an open source project started by Google to help developers optimize their web pages by applying best practices in web performance.
Page Speed began as an extension of the open source browser, and is now deployed in third party products as Webpagetest.org, Show Slow and Google Webmaster Tools.
How it works :
The Page Speed extensions run performance tests on the basis of a set of best practices known to reduce page load time.
mod_pagespeed, the Apache module, automatically optimizes the resources in a web page.
First you need to download the module from here: mod-pagespeed download
Then run the following commands to install it:
dpkg -i mod-pagespeed-*.deb apt-get -f install
After you installed the plugin you must restart the apache2 server.
Configure mod_pagespeed for using on VirtualHosts: