FastCGI is a binary protocol for interfacing interactive programs with a web server.
It is a variation on the earlier Common Gateway Interface (CGI).
FastCGI's main aim is to reduce the overhead related to interfacing between web server and CGI programs, allowing a server to handle more web page requests per unit of time.
History
Common Gateway Interface (CGI) is a protocol for interfacing external applications to web servers.
CGI applications run in separate processes, which are created at the start of each request and torn down at the end.
This "one new process per request" model makes CGI programs very simple to implement, but limits efficiency and scalability.
At high loads, the operating system overhead for process creation and destruction becomes significant.
Also, the CGI process model limits resource reuse methods, such as reusing database connections, in-memory caching, etc.
To address the scalability shortcomings of CGI, Open Market developed FastCGI and first introduced it in their webserver product in the mid-1990s.
Open Market originally developed FastCGI in part as a competitive response to Netscape's proprietary, in-process application programming interfaces (APIs) (Netscape Server Application Programming Interface (NSAPI)) for developing Web applications.
While developed first by Open Market, FastCGI was then implemented by several other webserver makers.
However, its approach competed against other methods to speed and simplify server-subprogram communication.
Apache HTTP Server modules such as mod_perl and mod_php appeared around the same time, and gained popularity quickly. , all of these various methods, including CGI, remain in common use.
Implementation details
Instead of creating a new process for each request, FastCGI uses persistent processes to handle a series of requests.
These processes are owned by the FastCGI server, not the web server.
To service an incoming request, the web server sends environment variable information and the page request to a FastCGI process over either a Unix domain socket, a named pipe, or a Transmission Control Protocol (TCP) connection.
Responses are returned from the process to the web server over the same connection, and the web server then delivers that response to the end user.
The connection may be closed at the end of a response, but both web server and FastCGI service processes persist.
Each individual FastCGI process can handle many requests over its lifetime, thereby avoiding the overhead of per-request process creation and termination.
Processing multiple requests concurrently can be done in several ways: by using one connection with internal multiplexing (i.e., multiple requests over one connection); by using multiple connections; or by a mix of these methods.
Multiple FastCGI servers can be configured, increasing stability and scalability.
Web site administrators and programmers can find that separating web applications from the web server in FastCGI has many advantages over embedded interpreters (mod_perl, mod_php, etc.).
This separation allows server and application processes to be restarted independently – an important consideration for busy web sites.
It also enables the implementation of per-application, hosting service security policies, which is an important requirement for ISPs and web hosting companies.
Different types of incoming requests can be distributed to specific FastCGI servers which have been equipped to handle those types of requests efficiently.
Web servers that implement FastCGI
Note: unless stated, completeness of FastCGI implementation is unknown
Apache HTTP Server (partial)
Implemented by .
This module used to be third-party, but was granted to The Apache Software Foundation (ASF) as an Apache Server subproject in 2009, shepherded by Chris Darroch.FastCGI apache module mod_fcgid It only supports Unix domain sockets, no TCP sockets.Debian bug #450748: Please add support for TCP/IP FastCGI servers
A third-party module  is also being used.
For a while, this module no longer compiled properly under Apache 2.4.x,Issues with Apache 2.4 and PHP-FPM although that problem has been solved with a fork of the original project.libapache-mod-fastcgi on Github
Multiplexing of requests through one connection is prohibited by Apache 1.x design, so this isn't supported
In Apache 2.4,  was added, supporting TCP FastCGI servers.
CaddyCaddy User Guide – FastCGI
CherokeeFastCGI for Cherokee
HiawathaFastCGI howto for Hiawatha
Loadbalancing FastCGI support
Supports chrooted FastCGI servers
JettyFastCGI Support in Jetty
Kerio WebSTAR
LighttpdFastCGI for Lighttpd
LiteSpeed Web Server
Microsoft IIS
Nginx
NaviServer
Oracle iPlanet Web Server
OpenBSD's OpenBSD's httpd(8) initial commit
Open Market web server
Resin web and application server
Roxen web server
ShimmerCat web server
Zeus Web Server
Language bindings for its API
FastCGI can be implemented in any language that supports network sockets.
Since "FastCGI is a protocol, not an implementation," it is not tightly bound to any one language.
Application programming interfaces (APIs) exist for:Application Libraries, Development Kits
Recent frameworks such as Ruby on Rails, Catalyst, Django, Kepler and Plack allow use with either the embedded interpreters (mod_ruby, mod_perl, mod_python or mod_lua, for example), or FastCGI.
References
External links
FastCGI Web official Site fork
FastCGI specification (site backup)
Secondary backup
mod_fastcgi – FastCGI module fork for Apache 1.x and 2.x supporting external applications
mod_fcgid A FastCGI module for Apache 2.x
Microsoft FastCGI
Apache v2.x mod_proxy FastCGI Module
