by Steve “Ashcrow” Milner and Anderson Silva
In today’s world, web development is all about turnaround. Businesses want to maximize production outcome while minimizing development and production time. Small, lean development teams are increasingly becoming the normal large development departments. Enter Django: a popular Python web framework that invokes the RWAD (rapid web application development) and DRY (don’t repeat yourself) principles with clean, pragmatic design.
This article is not about teaching you how to program in Python, nor how to use the Django framework. It’s about showing how to promote your Django applications onto an existing Apache or Lighttpd environment.
We will conclude with a simple way that you can improve the performance of your Django application by using caching to speed up access time. This article also assumes that you are running Fedora as your web application server, but all the packages mentioned in this article are also available under the Extra Packages for Enterprise Linux repository , which means these instructions should also be valid under Red Hat Enterprise Linux or CentOS servers.
What you need
You must have Django installed:
# yum install Django
If you want to serve Django apps under Apache:
# yum install httpd # yum install mod_python
If you want to serve Django apps under Lighttpd:
# yum install lighttpd # yum install lighttpd-fastcgi # yum install python-flup
Installing memcached to ‘speed up’ Django apps:
# yum install memcached # yum install python-memcached
Starting a new Django project
1. Create a development workspace.
$ mkdir -p $LOCATION_TO_YOUR_DEV_AREA $ cd $LOCATION_TO_YOUR_DEV_AREA
2. Start a new base Django project. This creates the boiler plate project structure.
$ django-admin.py startproject my_app
3. Start the Django development web server on port 8080 (or whatever other port you’d like).
Note: The development web server is just for testing and verification. Do not use it as a production application server!
$ python manage.py runserver 8080
4. Run your Django project under Apache with mod_python by enabling mod_python on httpd.conf (/etc/httpd/conf/httpd.conf).
After installing mod_python, a file called python.conf should already be placed in /etc/httpd/conf.d/, which enables mod_python on your system.
5. Create virtual hosts by creating a new file at /etc/httpd/conf.d/myapp.conf.
DocumentRoot /var/www/html/ ServerName your_domain_name ErrorLog logs/my_app-error.log CustomLog logs/my_app-access_log common SetHandler python-program PythonHandler django.core.handlers.modpython SetEnv DJANGO_SETTINGS_MODULE my_app.settings PythonDebug On PythonPath "['/var/www/django/'] + sys.path"
Running your Django project under Lighthttpd with fastcgi
The first thing you must do is start up your FastCGI server.
./manage.py runfcgi method=prefork socket=/var/www/myapp.sock pidfile=django_myapp.pid
Then modify your lighttpd.conf file to use the FastCGI server.
server.document-root = "/var/www/django/" fastcgi.server = ( "/my_app.fcgi" => ( "main" => ( # Use host / port instead of socket for TCP fastcgi # "host" => "127.0.0.1", # "port" => 3033, "socket" => "/var/www/my_app.sock", "check-local" => "disable", ) ), ) alias.url = ( "/media/" => "/var/www/django/media/", ) url.rewrite-once = ( "^(/media.*)$" => "$1", "^/favicon\.ico$" => "/media/favicon.ico", "^(/.*)$" => "/my_app.fcgi$1", )
Setting up caching in Django
Django has many different caching backends, including database, memory, filesystem, and the ever popular memcached. According to http://www.danga.com/memcached/, memcached is “a high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load.” It’s used by high traffic sites such as Slashdot and Wikipedia. This makes it a prime candidate for caching in your cool new web app.
First, verify that memcached is running using the memcached’s init script.
$ /etc/init.d/memcached status memcached (pid 6771) is running...
If it’s not running, you can manually start it.
$ /sbin/service memcached start
If you want to make sure it will automatically start every time after a reboot:
$ /sbin/chkconfig --level 35 memcached on
Now that you have verified that memcached is running, you will want to tell your Django application to use memcached as it’s caching backend. You can do this by adding a CACHE_BACKEND entry to your settings.py file.
CACHE_BACKEND = 'memcached://127.0.0.1:11211/'
The format is “backend://host:port/” or “backend:///path” depending on the backend chosen. Since we are using memcached, we have the option to run multiple daemons on different servers and share the cache across multiple machines. If you want to do this all you must do is add in the servers:port combinations in the CACHE_BACKEND and separate them by semicolons. In this example we share the cache across three different memcached servers:
CACHE_BACKEND = 'memcached://127.0.0.1:11211;192.168.0.10:11211;192.168.0.11/'
For more information on the different types of caching that can be performed in the Django framework, please refer to their official documentation.