The WSGI specification provides a standard and efficient method for dynamic web applications to communicate with web servers. mod_wsgi provides a method for simply deploying WSGI applications with Apache. WSGI is used to deploy applications written with frameworks and tools like Django, Web.py, Werkzug, Chery.py, TurboGears, and Flask. These guides outline this installation and configuration process for deploying WSGI applications.
Before you begin installing and configuring the components described in this guide, please make sure you’ve followed our instructions for setting your hostname. Issue the following commands to make sure it is set properly:
hostname hostname -f
The first command should show your short hostname, and the second should show your fully qualified domain name (FQDN).
Issue the following commands to ensure that your system’s package repositories and installed programs are up to date and that all required software is installed:
apt-get update apt-get upgrade apt-get install apache2 python-setuptools libapache2-mod-wsgi
Your application may require additional dependencies. Install these either using the Ubuntu package tools or by using the easy_install command included in python-setuptools before proceeding.
In order for mod_wsgi to be able to provide access to your application, you will need to create a application.wsgi file inside of your application directory. The application directory should be located outside of your DocumentRoot. The following three sections each present a different application.wsgi example file to illustrate the basic structure of this file:
In this example, the application is stored in /srv/www/ducklington.org/application directory. Modify this example and all following examples to conform to the actual files and locations used in your deployment.
import os import sys sys.path.append('/srv/www/ducklington.org/application') os.environ['PYTHON_EGG_CACHE'] = '/srv/www/ducklington.org/.python-egg' def application(environ, start_response): status = '200 OK' output = 'Hello World!' response_headers = [('Content-type', 'text/plain'), ('Content-Length', str(len(output)))] start_response(status, response_headers) return [output]
You must append the path of your application to the system path as above. The declaration of the PYTHON_EGG_CACHEvariable is optional but may be required for some applications when WSGI scripts are executed with the permissions of the web server. The WSGI application must be callable as “application“, regardless of how the application code is structured.
Consider the following example Web.py application which is embeded in a application.wsgi file. The Web.py Framework must be installed in order for the following application to run successfully.
import web urls = ( '/(.*)', 'hello' ) class hello: def GET(self, name): if not name: name = 'World' return 'Hello, ' + name + '!' if __name__ == "__main__": app.run() app = web.application(urls, globals(), autoreload=False) application = app.wsgifunc()
Consider the following example application.wsgi file for Django applications:
import os import sys sys.path.append('/srv/www/ducklington.org/application') os.environ['PYTHON_EGG_CACHE'] = '/srv/www/ducklington.org/.python-egg' os.environ['DJANGO_SETTINGS_MODULE'] = 'settings' import django.core.handlers.wsgi application = django.core.handlers.wsgi.WSGIHandler()
Django must be installed on your system and a working Django application before this example will function. The “DJANGO_SETTINGS_MODULE” points to the “settings.py file for your application, which would be located in the “/srv/www/ducklington.org/application/settings.py in the case of this example.
Deploy the following VirtualHost configuration and modify the paths and domains to reflect the requirements of your application:
File excerpt:Apache “VirtualHost“ Configuration
<VirtualHost *:80> ServerName ducklington.org ServerAlias www.ducklington.org ServerAdmin firstname.lastname@example.org DocumentRoot /srv/www/ducklington.org/public_html ErrorLog /srv/www/ducklington.org/logs/error.log CustomLog /srv/www/ducklington.org/logs/access.log combined WSGIScriptAlias / /srv/www/ducklington.org/application/application.wsgi Alias /robots.txt /srv/www/ducklington.org/public_html/robots.txt Alias /favicon.ico /srv/www/ducklington.org/public_html/favicon.ico Alias /images /srv/www/ducklington.org/public_html/images Alias /static /srv/www/ducklington.org/public_html/static </VirtualHost>
In this example, the WSGIScriptAlias directive tells Apache that for this VirtualHost, all requests below / should be handled by the WSGI script specified. The series of four Alias directives allow Apache to serve the robots.txt andfavicon.ico files as well as all resources beneath the /images and /static locations, directly from theDocumentRoot without engaging the WSGI application. You can add as many Alias directives as you require.
When you have configured your Apache VirtualHost, issue the following command to restart the web server:
You will need to restart the web server every time the application.wsgi file changes. However, all other modifications to your application do not require a web server restart. Congratulations! You have now successfully deployed a WSGI application using mod_wsgi.
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