FastCGI is really CGI on steroids

FastCGI is very common way to increase performance of a CGI installation. It is based on the fact that usually the startup of CGI scripts is slow, whereas the response is quite fast.

So if you have a persistent process, you only have to take care of the startup once, and you then experience a real speedup.

FastCGI vs mod_perl (or mod_python, ...)

Once a big fan of mod_perl, I'm converted to FastCGI since. mod_perl was for a long time the answer for speeding up Perl CGI scripts. It has a very good track record of stability and has real hooks deep in the Apache processing requests.

FastCGI focuses on a different feature set that is more actual than mod_perl[1] :

  • It is much simpler to install and configure, especially when having multiple applications.
  • Able to connect to a distant server (running as a different UID, chrooted or even on a remote host)
  • Able to mix scripting languages without any need to compile some other apache modules.
  • Able to be used with several webservers, even closed-source ones : FastCGI is a protocol, not an API.

But steroids do have some side effects

CGI issues

One downside is that your CGI script should be adapted to FastCGI and the fact that the script doesn't end with the end of the request.

In the real world that's quite easy. Every language that is commonly used for CGI offers CGI-wrapper libraries that works in a FastCGI context as well as a plain CGI one.

Webserver issues

Another issue can also come from the webserver. Since CGI is dead simple to implement even the micro-webserver thttpd implements it.

FastCGI on the other hand is a little more difficult to implement, since the webserver needs to create a container that monitors and calls the FastCGI-enabled script.

A standalone FastCGI container

Fortunately, the FastCGI team provided us with a ready-to-use container and a very simple client that acts a plain CGI script, but proxies it to a full-blown container.

Since the plain CGI part is a very small native executable its overhead is negligible compared to the reply time, even without comparison with the startup time of the whole script.

Its installation is also quite straightforward. I just installed the libfcgi package on Debian : it provides /usr/bin/cgi-fcgi.

I created a simple CGI wrapper for my previous munin benchmarking needs :

#! /bin/sh

exec /usr/bin/cgi-fcgi -connect /tmp/munin-cgi.sock \
     /usr/lib/cgi-bin/munin-cgi-graph

Notes

[1] who really need deep apache hooks ?