Zend is aiming to improve the scalability of PHP for large-scale deployments and the cloud with the release of Zend Server Cluster Manager, a system for managing multiple PHP servers.

Zend Server is a bundled PHP middleware server that provides both the PHP language as well as an Apache Web server with database connectivity. Zend Server itself is available as both a community version and a commercial version, but the cluster manager is available only in a commercial version.

Get all the details here: http://www.developer.com/features/article.php/3889726/Zend-Scales-PHP-Server-with-Cluster-Edition.htm