PHP fastCGI Process Manager is an alternative PHP FastCGI implementation with some additional features (mostly) useful for heavy-loaded sites.
Internally, PHP-FPM is organized as a “master process” managing pools of individual “worker processes.” When the web server has a request for a PHP script, the web server uses a proxy, FastCGI connection to forward the request to the PHP-FPM service. The PHP-FPM service can listen for these requests on the host server’s network ports or through Unix sockets. Although requests pass via a proxy connection, the PHP-FPM service must run on the same server as the web server. Notably, the proxy connection for PHP-FPM is not the same as a traditional proxy connection. As PHP-FPM receives a proxied connection, a free PHP-FPM worker accepts the web server’s request. PHP-FPM then compiles and executes the PHP script, sending the output back to the web server. Once a PHP-FPM worker finishes handling a request, the system releases the worker and waits for new requests.