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Running TurboGears 2.1 behind Apache with Mod Proxy

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FastCGI/WSGI – Running TurboGears 2.1 behind Apache

Warning

We recommend that, where possible, you use Apache Mod-WSGI as that is part of the Standard Deployment Pattern

FastCGI is an appropriate choice when:

  • mod_wsgi and mod_python are not available
  • you cannot run the Pylons/Paste web-server directly on port 80 (likely because Apache is already running on port 80)
  • mod_fcgi and mod_rewrite are available (common)

Because TurboGears implements the WSGIServer interface, we can use flup to interface between FastCGI and Pylons. We’ll also show you how to use VirtualEnv in this setup.

This document is closely analogous to _Pylon’s instructions for CGI: http://wiki.pylonshq.com/display/pylonscookbook/Production+Deployment+Using+Apache,+FastCGI+and+mod_rewrite but have a number of key differences.

Apache Configuration

Discussing what Apache directives should be set is beyond the scope of this document, but mod_fastcgi and mod_rewrite should be enabled. Most webhosts have the latter enabled by default; some require you to explicitly enable FastCGI via their control panel (Dreamhost is one such host).

Installation

If you setup your own virtualenv according to the instructions on the installation page, you will need to install flup, with:

$ easy_install flup

If you are not using virtualenv, check to see if flup is installed or not with import flup.

Dispatch scripts

Keeping your TurboGears install in a web-accessible directory is strictly unnecessary; the only files we will need to add to forward FastCGI are dispatch.fcgi and an .htaccess file.

dispatch.fcgi

In the dispatch.fcgi file, you will need the following boilerplate code:

#!/usr/bin/env python
turbogears = '/usr/local/turbogears/myapp'
inifile = 'production.ini'
import sys, os
sys.path.insert(0, turbogears)
from paste.deploy import loadapp
wsgi_app = loadapp('config:' + turbogears + '/' + inifile
if __name__ == '__main__':
    from flup.server.fcgi import WSGIServer
    WSGIServer(wsgi_app).run()

There are three locations in this file that you may need to edit:

  1. The turbogears variable should be set to the location of your TurboGears codebase, i.e. where you can find such files as development.ini and setup.py
  2. The inifile variable should be set to the name of the configuration file you would like to be loaded on this server.
  3. The shebang line (#!/usr/bin/env python) should be modified to use the virtualenv Python interpreter, if you are using such an environment.

This loader file is different from the Pylons flup file, please be careful! Also, you need to make this file executable, with:

$ chmod 0755 dispatch.fcgi

.htaccess

You will need to add the following lines to your .htaccess file:

Options +ExecCGI
AddHandler fastcgi-script .fcgi
RewriteEngine On
RewriteRule   ^(dispatch\.fcgi/.*)$  - [L]
RewriteRule   ^(.*)$  dispatch.fcgi/$1 [L]

You can also setup static content with an extra RewriteRule before the last line:

RewriteRule ^(static/.*)$ - [L]

The first two lines (Options and AddHandler) may not be strictly necessary, depending on your web server’s configuration.

Proxy Mount Point Fix

Using this method, Turbogears/Pylons wrongly thinks that dispatch.fcgi is a part of the URL. See Configure Proxy Mount Point for how to fix this in your production.ini.

Maintenance

Checking if it worked

The most obvious metric for success is whether or not your site displays on your browser. However, you can also check with ps aux | grep dispatch to see if your FastCGI executable is still running.

Rebooting

Because FastCGI processes are persistent, even when you update your Python files the old code will still be running. Usually, the following command from your shell will be sufficient to kill the process:

$ killall -u username dispatch.fcgi

If dispatch.fcgi is running as the Apache user, i.e. www-data, you’ll need to create a short Python stub script to call from the web in order to execute this command. (Also, your host is doing it wrong.)

Debugging

FastCGI is notoriously difficult to debug. There are variants of dispatch.fcgi which add lots of informative debugging output; you can also rename the file to dispatch.cgi and run as a CGI module (it will not be as fast, but will be reloaded every request).