Apache HTTP Server v1.3 or v2.x with SSL enabled - while VCL may run under another webserver capable of running PHP code, it has only been tested to work with Apache HTTP Server
PHP 5
php modules that should be installed (depending on your Linux distro, some of these may be compiled in to php instead of being a separate module):
php-gd
php-json (if your PHP version is < 5.2, this is not required)
php-mcrypt
php-mysql
php-openssl
php-sysvsem
php-xml
php-xmlrpc
If you are running RedHat or CentOS, these can be installed with