Django, Apache and mod_wsgi on CentOS 5

Django is a web development framework for the Python programing language. It enables rapid development, while favoring pragmatic and clean design. Django was initially developed for use in a newspaper’s website division, and as a result the Django framework is very well suited to developing content-centric applications.

This guide provides an introduction to getting started with the Django framework, using the mod_wsgi method of deploying python applications. Please complete the Setting Up and Securing a Compute Instance prior to beginning this guide on an up to date system. Furthermore, you will want a running Apache web server and a functional MySQL database system installed.

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).

Before beginning to install software required for the deployment of Django applications, install the EPEL repositories which contain required packages that are not present in the main CentOS repositories:

rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm

When you install your first package from EPEL, yum will ask you to import the PGP key for the EPEL repository. You should accept this request. Issue the following commands to ensure that your system’s package repositories and installed programs are up to date and all required software is installed:

yum update
yum install python-setuptools httpd mod_wsgi

Additionally you will need to install a database system and a python driver for this database system. If you want to run the PostgreSQL database server issue the following command:

yum install postgresql python-psycopg2

If you want to use the SQLite embedded database, issue the following command:

yum install sqlite python-sqlite

If you want to run the MySQL database engine, download and install a more recent version of the MySQL-python package. Django requires at least version 1.2.1p2 of the Python MySQLdb adapter. We’ll download and install a later version from the upstream project First, install the tools needed to build this package:

yum install python-devel mysql-devel gcc wget python-setuptools

Check the Python MySQLdb page for information regarding the latest release, then issue the following commands. This will download the archive of the source files, extract them from the archive, build the database adapter, and install the files on to your system.

cd /opt/
wget http://downloads.sourceforge.net/project/mysql-python/mysql-python/1.2.3/MySQL-python-1.2.3.tar.gz
tar -zxvf MySQL-python-1.2.3.tar.gz
cd MySQL-python-1.2.3/
python setup.py build
python setup.py install

Your application may require additional dependencies. You may install these either using the CentOS package tools or by using the easy_install command included in python-setuptools.

There are two methods for installing Django. You may either choose to install the Django packages from the EPEL repositories, or you can install using the python easy_install method. Installing the EPEL packages will install version 1.1.1 of the framework, but you will have the benefit of ongoing security and bug fixes from the Fedora Project if you install by way of the EPEL repositories. To install Django in this manner:

yum install Django

If you want to install Django using the easy_install tool, issue the following command:

easy_install Django

At the time of writing, this will install version 1.2.5 of the Django framework. Consider the package information for Django for more information.

In order for mod_wsgi to be able to provide access to your Django application, you will need to create a django.wsgi file inside of your application directory. For the purposes of this example, we assume that your application will be located outside of your DocumentRoot in the directory /srv/www/example.com/application. Modify this example and all following examples to conform to the actual files and locations used in your deployment.

File: /srv/www/example.com/application/django.wsgi

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import os import sys sys.path.append('/srv/www/example.com/application') os.environ['PYTHON_EGG_CACHE'] = '/srv/www/example.com/.python-egg' os.environ['DJANGO_SETTINGS_MODULE'] = 'settings' import django.core.handlers.wsgi application = django.core.handlers.wsgi.WSGIHandler()

You must append the path of your application to the system path as above. Additionally, declaration of the PYTHON_EGG_CACHE variable is optional but may be required for some applications when WSGI scripts are executed with the permissions of the web server. Finally, the DJANGO_SETTINGS_MODULE must refer to the Django settings.py file for your project. You will need to restart Apache after modifying the django.wsgi file.

Consider the following example virtual host configuration:

File: Apache Virtual Host Configuration

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<VirtualHost example.com:80> ServerName example.com ServerAlias www.example.com ServerAdmin username@example.com DocumentRoot /srv/www/example.com/public_html WSGIScriptAlias / /srv/www/example.com/application/django.wsgi <Directory /srv/www/example.com/application> Order allow,deny Allow from all </Directory> Alias /robots.txt /srv/www/example.com/public_html/robots.txt Alias /favicon.ico /srv/www/example.com/public_html/favicon.ico Alias /images /srv/www/example.com/public_html/images Alias /static /srv/www/example.com/public_html/static ErrorLog /srv/www/example.com/logs/error.log CustomLog /srv/www/example.com/logs/access.log combined </VirtualHost>

In this example, the WSGIScriptAlias directive tells Apache that for this virtual host, all requests below / should be handled by the WSGI script specified. In the directory block that follows, we allow Apache to serve these requests. Finally, the series of four Alias directives allow Apache to serve the robots.txt and favicon.ico files as well as all resources beneath the /images and /static locations, directly from the DocumentRoot without engaging the WSGI application. You can add as many Alias directives as you need to.

Edit the /etc/httpd/conf.d/wsgi.conf file to enable the mod_wsgi by uncommenting or adding the following line:

File: /etc/httpd/conf.d/wsgi.conf

1	LoadModule wsgi_module modules/mod_wsgi.so

When you have successfully configured your Apache virtual host, and enabled the required module, issue the following command to restart the web server:

/etc/init.d/httpd restart

Now issue the following command to ensure that Apache will start after a reboot cycle, if you have not already:

chkconfig httpd on

You will need to restart the web server every time the django.wsgi file changes. However, all other modifications to your application do not require a web server restart. Congratulations! You have now successfully deployed a Django application using mod_wsgi.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• The Django Project Home Page
• The Django Project Introductory Tutorial
• The Django Book
• Deploying Django Applications
• A Basic “Hello World” Django Application
• Integrating Django and mod_wsgi