In Symfony the stylesheets and javascript files are defined in the view.yml. Sometimes the problem appears that the browsers cache these files, even if there where some changes in the last release without refreshing the new contents.

There is a common technique to instruct the browser to take the new file version: Browsers store different file versions for different GET paramters. So if you include a CSS file like this:

<script type="text/javascript" src="css/styles.css?v=21"></script>

and in the next version with a higher version number (v=22), the browser will use  (and cache) the newer version.

In our case we save the current version number (SVN) into the app.yml and we use this number as increasing GET-Parameter to force a cache refresh:

default:
  stylesheets: [styles.css?v=<?php echo sfConfig::get('app_revision'); ?>]