# Web Server Configuration for Quixote

For a simple Quixote installation, there are two things you have to get right:

- installation of the Quixote modules to Python's library (the trick here is that the `quixote` package must be visible to the user that CGI scripts run as, not necessarily to you as an interactive command-line user)
- configuration of your web server to run Quixote driver scripts

This document is concerned with the second of these.

# Which web servers?

We are only familiar with Apache, and we develop Quixote for use under Apache. However, Quixote doesn't rely on any Apache-specific tricks; if you can execute CGI scripts, then you can run Quixote applications (although they'll run a lot faster with mod_scgi or FastCGI). If you can redirect arbitrary URLs to a CGI script and preserve parts of the URL as an add-on to the script name (with `PATH_INFO`), then you can run Quixote applications in the ideal manner, ie. with superfluous implementation details hidden from the user.

# Which operating systems?

We are mainly familiar with Unix, and develop and deploy Quixote under Linux. However, we've had several reports of people using Quixote under Windows, more-or-less successfully. There are still a few Unix-isms in the code, but they are being rooted out in favor of portability.

Remember that your system is only as secure as its weakest link. Quixote can't help you write secure web applications on an inherently insecure operating system.

# Basic CGI configuration

Throughout this document, I'm going to assume that:

- CGI scripts live in the `/www/cgi-bin` directory of your web server, and have the extension `.cgi`
- HTTP requests for `/cgi-bin/foo.cgi` will result in the execution of `/www/cgi-bin/foo.cgi` (for various values of `foo`)
- if the web server is instructed to serve an executable file `bar.cgi`, the file is treated as a CGI script

With Apache, these configuration directives will do the trick:

    AddHandler cgi-script .cgi
    ScriptAlias /cgi-bin/ /www/cgi-bin/

Consult the Apache documentation for other ways of configuring CGI script execution.

For other web servers, consult your server's documentation.

# Installing driver scripts

Given the above configuration, installing a Quixote driver script is the same as installing any other CGI script: copy it to `/www/cgi-bin` (or whatever). To install the Quixote demo's cgi driver script:

    cp -p server/cgi_server.py /www/cgi-bin/demo.cgi

(The `-p` option ensures that `cp` preserves the file mode, so that it remains executable.)

# URL rewriting

With the above configuration, users need to use URLs like

    http://www.example.com/cgi-bin/demo.cgi

to access the Quixote demo (or other Quixote applications installed in the same way). This works, but it's ugly and unnecessarily exposes implementation details.

In our view, it's preferable to give each Quixote application its own chunk of URL-space -- a "virtual directory" if you like. For example, you might want

    http://www.example.com/qdemo

to handle the Quixote demo.

With Apache, this is quite easy, as long as mod_rewrite is compiled, loaded, and enabled. (Building and loading Apache modules is beyond the scope of this document; consult the Apache documentation.)

To enable the rewrite engine, use the

    RewriteEngine on

directive. If you have virtual hosts, make sure to repeat this for each `<VirtualHost>` section of your config file.

The rewrite rule to use in this case is

    RewriteRule ^/qdemo(/.*) /www/cgi-bin/demo.cgi$1 [last]

This is not a redirect; this is all handled with one HTTP request/response cycle, and the user never sees `/cgi-bin/demo.cgi` in a URL.

Note that requests for `/qdemo/` and `/qdemo` are not the same; in particular, with the above rewrite rule, the former will succeed and the latter will not. (Look at the regex again if you don't believe me: `/qdemo` doesn't match the regex, so `demo.cgi` is never invoked.)

The solution for `/qdemo` is the same as if it corresponded to a directory in your document tree: redirect it to `/qdemo/`. Apache (and, presumably, other web servers) does this automatically for "real" directories; however, `/qdemo/` is just a directory-like chunk of URL-space, so either you or Quixote have to take care of the redirect.

It's almost certainly faster for you to take care of it in the web server's configuration. With Apache, simply insert this directive before the above rewrite rule:

    RewriteRule ^/qdemo$ /qdemo/ [redirect=permanent]

If, for some reason, you are unwilling or unable to instruct your web server to perform this redirection, Quixote will do it for you. However, you have to make sure that the `/qdemo` URL is handled by Quixote. Change the rewrite rule to:

    RewriteRule ^/qdemo(/.*)?$ /www/cgi-bin/demo.cgi$1 [last]

Now a request for `/qdemo` will be handled by Quixote, and it will generate a redirect to `/qdemo/`. If you're using a CGI driver script, this will be painfully slow, but it will work.

For redirecting and rewriting URLs with other web servers, consult your server's documentation.

# Long-running processes

For serious web applications, CGI is unacceptably slow. For a CGI-based Quixote application, you have to start a Python interpreter, load the Quixote modules, and load your application's modules before you can start working. For sophisticated, database-backed applications, you'll probably have to open a new database connection as well for every hit.

Small wonder so many high-performance alternatives to CGI exist. (The main advantages of CGI are that it is widely supported and easy to develop with. Even for large Quixote applications, running in CGI mode is nice in development because you don't have to kill a long-running driver script every time the code changes.) Quixote includes support for mod_scgi and FastCGI.

# mod_scgi configuration

SCGI is a CGI replacement written by Neil Schemenauer, one of Quixote's developers, and is similar to FastCGI but is designed to be easier to implement. mod_scgi simply forwards requests to an already-running SCGI server on a different TCP port, and doesn't try to start or stop processes, leaving that up to the SCGI server.

The SCGI code is available from http://www.mems-exchange.org/software/scgi/ .

The quixote.server.scgi_server module is a script that publishes the demo quixote application via SCGI. You can use it for your application by importing it and calling the `run()` function with arguments to run your application, on the port you choose. Here is an example:

    #!/usr/bin/python
    from quixote.server.scgi_server import run
    from quixote.publish import Publisher
    from mymodule import MyRootDirectory

    def create_my_publisher():
        return Publisher(MyRootDirectory())

    run(create_my_publisher, port=3001)

The following Apache directive will direct requests to an SCGI server running on port 3001:

    <Location />
      SCGIServer 127.0.0.1 3001
      SCGIHandler On
    </Location>

[Note: the mod_scgi module for Apache 2 requires a colon, instead of a space, between the host and port on the SCGIServer line.]

# SCGI through CGI

Recent releases of the scgi package include cgi2scgi.c, a small program that offers an extremely convenient way to take advantage of SCGI using Apache or any web server that supports CGI. To use it, compile the cgi2scgi.c and install the compiled program as usual for your webserver. The default SCGI port is 3000, but you can change that by adding `-DPORT=3001` (for example) to your compile command.

Although this method requires a new process to be launched for each request, the process is small and fast, so the performance is acceptable for many applications.

# FastCGI configuration

If your web server supports FastCGI, you can significantly speed up your Quixote applications with a simple change to your configuration. You don't have to change your code at all (unless it makes assumptions about how many requests are handled by each process). (See http://www.fastcgi.com/ for more information on FastCGI.)

To use FastCGI with Apache, you'll need to download mod_fastcgi from http://www.fastcgi.com/ and add it to your Apache installation.

Configuring a FastCGI driver script is best done after reading the fine documentation for mod_fastcgi at http://www.fastcgi.com/mod_fastcgi/docs/mod_fastcgi.html

However, if you just want to try it with the Quixote demo to see if it works, add this directive to your Apache configuration:

    AddHandler fastcgi-script .fcgi

and copy server/fastcgi_server.py to demo.fcgi. If you're using a URL rewrite to map requests for (eg.) `/qdemo` to `/www/cgi-bin/demo.cgi`, be sure to change the rewrite -- it should now point to `/www/cgi-bin/demo.fcgi`.

After the first access to `demo.fcgi` (or `/qdemo/` with the modified rewrite rule), the demo should be noticeably faster. You should also see a `demo.fcgi` process running if you do `ps -le` (`ps -aux` on BSD-ish systems, or maybe `ps aux`). (On my 800 MHz Athlon machine, there are slight but perceptible delays navigating the Quixote demo in CGI mode. In FastCGI mode, the delay between pages is no longer perceptible -- navigation is instantaneous.) The larger your application is, the more code it loads, and the more work it does at startup, the bigger a win FastCGI will be for you (in comparison to CGI).