[[!meta title="How do I enable FastCGI?"]]
### CGI vs FastCGI

Normal CGI scripts are initialized, run, and destroyed for every
single browser request. The advantage of this model is that it is
very simple, and thus robust.

If performance or latency becomes an issue, you can enable FastCGI.
FastCGI is a web server module that speeds up your applications by
keeping one interpreter running for multiple requests, instead of
launching a separate interpreter for each request made while
loading your page.

### When FastCGI can help

This can lead to improvements in latency (responsiveness), for
example if:

-   The language you are using takes a long time to start an
    interpreter, or to load libraries you are importing
-   You have a script which has significant repetitive launching
    overhead
-   Your scripts make the same, very large, database requests which
    (while cached by MySQL) still have to be read from memory and
    possibly cross an internal network
-   You are using a web framework like CherryPy, Turbogears,
    Pylons, or Ruby on Rails which prefers to run like a daemon

### Caveats

There are some complications however:

-   The script in not guaranteed to die unless it kills itself
-   If you update your fcgi script, the old process (using the old
    script) may still be running with outdated code
-   The Scripts service automatically load-balances scripts across
    servers, just like regular CGI; new scripts may not even be
    launched on the servers the old scripts are running on, and thus
    cannot “kill all older versions of myself” since they may be on
    different servers

The canonical way around these issues is to have the script watch
the timestamps of the files it has loaded, and kill itself if a
modification timestamp changes. If you are using a framework such
as CherryPy, this is already handled for you.

(Minor note: This method lends itself to race conditions on very
short timescales during an update. It is also expensive if you are
watching many files. Other solutions include updating a single
“watch me” file with a version or hash after every update, or using
transactional semantics. This is almost never an issue however.)

### Enabling FastCGI

FastCGI is enabled by default for files with the **.fcgi**
extension. To enable FastCGI for another extension, such as .rb,
add the following lines to a plain text file named **.htaccess** in
the top directory of your website:

**<Files \*.rb\>  
  SetHandler fcgid-script  
</Files\>**

To enable FastCGI for another languages, change **rb** to your
language’s extension (e.g., **php**, **pl**, etc.)