Varnish manages all cache content following the rules it receives in HTTP headers from both the visitor and your application. Making modifications to the Varnish configuration in order to change its behaviour is really only necessary in rare edge cases. Instead, simply make sure your web application sends the appropriate HTTP headers.
For example, creating a file
/sites/default/files/nocache/.htaccess with the following contents will disable caching for all content below the
<IfModule mod_headers.c> Header unset ETag Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate" Header set Pragma "no-cache" Header set Expires "Wed, 18 Feb 1970 17:00:00 GMT" </IfModule>
WARNING Please be aware that disabling caching will increase the load on both your application boxes and the database, which will affect content delivery performance.