Deploying ViewCVS with WSGI

In my continuing expermentation with Python Paste I came across the cgiapp module. The module provides a class that acts as a proxy to an existing CGI script, which means you can take an existing CGI script and run it using a WSGI enabled server. Rather than testing it's functionality with a simple cgi script, decided to see if I could run ViewCVS with it. To get it to run was very simple.

Create a app factory wrapper script called viewcvs_wsgi.py

from paste import cgiapp

def app_factory(global_config, **local_config):
 
 viewcvs_app = cgiapp.CGIApplication(global_config, script, path=None, include_os_environ=True, query_string=None)
 return viewcvs_app

Create a Paste Deploy configuration file called viewcvs.ini

[app:main]
paste.app_factory = viewcvs_wsgi:app_factory
script = "/usr/local/viewcvs-0.9.4/cgi/viewcvs.cgi"

[server:main]
use = egg:PasteScript#wsgiutils
host = 192.168.1.1
port = 8082

Start the WSGIUtils webserver using paster

paster server viewcvs.ini

Point a browser to the URL and browse the CVS repository.

Apart from images not displaying everything else worked as normal. Now why would I want to do this? Well it means I can now run viewcvs under IIS as an ISAPI extension using my isapi_wsgi adaptor. But thats a future blog entry.

SyPy Meetup Last Night

Last night was the last meeting of the year for the Sydney Python group. Andy Todd did a test run of his OSDC presentation on PythonCard. Apart from having to cope with using a Windows laptop instead of his beloved iBook, it was very interesting introduction in how to use PythonCard. I gave a presentation on Python Paste and hopefully, a few more know now what it is. The discussion on Paste.Deploy prompted Graham Dumpleton to give an impromptu presentation on an extension for mod_python he is creating called lamia that as one of it's features uses Python as it's configuration language.

Confirming that Python programmers are happy to look at other languages Alan Green gave us a look at Groovy, the new Java scripting language.

As with all the meetups this year, lots of other interesting conversations and looking forward to next year. Thanks to Alan Green for organising all this years meetings.

Deploying a WSGI app with Python Paste

As part of my research of the current state of WSGI for my paper for OSDC2005 I revisited PythonPaste. Ian has added lots more functionality since I last looked and I wanted to use Python Paste as the "glue" for a demo of creating a web app from WSGI middleware components. As with most stuff Ian does, there was enough documentation to get me going or so I thought. In reality, it took me a lot longer to get things working than I originally planned. This is no reflection on Ian's docs, but more on me not "getting it", and trying to make the solution complex. So what follows is a little tutorial on how to deploy a very simple WSGI app using Paste.Deploy and Paste.Script under Ubuntu 5.10 Linux and Python 2.4. Also this tutorial only uses a very small subset of Paste functionality.

0. If you have not installed any Python packages using easy_install before, you will need to download it and install it following the instructions at this site.

1. Install paste, paste.deploy and paste.script using easy install

sudo easy_install http://cheeseshop.python.org/packages/2.4/P/Paste/Paste-0.3-py2.4.egg
sudo easy_install http://cheeseshop.python.org/packages/2.4/P/PasteDeploy/PasteDeploy-0.3-py2.4.egg
sudo easy_install http://cheeseshop.python.org/packages/2.4/P/PasteScript/PasteScript-0.3-py2.4.egg

Also install WSGIUtils so we have a WSGI server to run our WSGI app under.

sudo easy_install http://pylons.groovie.org/files/WSGIUtils-0.6-py2.4.egg

2. Create a simple WSGI app in a file called hello_wsgi.py

def application(environ, start_response):
    """Simple WSGI application"""
    status = '200 OK'
    response_headers = [('Content-type','text/plain')]
    start_response(status, response_headers)
    return ['Hello world!\n']

def app_factory(global_config, **local_config):
    """This function wraps our simple WSGI app so it
    can be used with paste.deploy"""
    return application

3. Create a paste deploy configuration file called config.ini

[app:main]
paste.app_factory = hello_wsgi:app_factory

[server:main]
use = egg:PasteScript#wsgiutils
host = localhost
port = 80

The first section app:main is where we define our application, or more simply tell paste.deploy where the code for our WSGI app can be found, in our case in the file hello_wsgi.py and by calling function app_factory.

The second section server:main tells paste.script what WSGI server to use. In this case we will be using the simple WSGI server that comes with WSGIUtils.

4. To serve the app we use the paster script that was installed as part of Paste.Script. So enter the following at the commandline.

export PYTHONPATH=.   # Ensure our hello_wsgi.py module can be imported by Python
sudo paster server ./config.ini

On the console, a message will be displayed similar to:

Starting server in PID 9582.

5. Enter the URL for the web app in a browser and hopefully you see hello world displayed.

6. Replace the boring hello world app with a more useful WSGI app you are now inspired to create.