NGINX - Determine if user agent is mobile and add set a different proxy_cache_key

gistfile1.txt

        location ~ / {

            # mobile users
            if ($http_user_agent ~* '(iPhone|iPod|mobile|Android|2.0\ MMP|240x320|AvantGo|BlackBerry|Blazer|Cellphone|Danger|DoCoMo|Elaine/3.0|EudoraWeb|hiptop|IEMobile)') {
                    set $ismobile '1';
            }

            proxy_cache_key             $proxy_host$uri$ismobile;
            add_header                  X-Is-Mobile $ismobile;

        }