Daniel: Chapter 12: Deploying Django

Deploying Django Application to a Production Server
Apache: industrial-strength Web Server

Preparing Your Codebase for Production

1. settings.py
DEBUG = False
TEMPLATE_DEBUG = False

2. root template directory
404.html

{% extends "base.html" %}

{% block title %}Page not found{% endblock %}

{% block content %}
<h1>Page not found</h1>

<p>Sorry, but the requested page could not be found.</p>
{% endblock %}

500.html
(not rely on other templates)
unhandled Python exception

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
    "http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
    <title>Page unavailable</title>
</head>
<body>
    <h1>Page unavailable</h1>

    <p>Sorry, but the requested page is unavailable due to a
    server hiccup.</p>

    <p>Our engineers have been notified, so check back later.</p>
</body>
</html>3. Setting Up Error Alters and Setting Up Broken Link Alerts

Need Email Set up

ADMINS = (
    ('John Lennon', 'jlennon@example.com'),
    ('Paul McCartney', 'pmacca@example.com'),
)

http://www.djangobook.com/en/2.0/chapter12.html

Using Multiple settings.py for Development and Production

Three ways:

Two independent settings files
base setting file and inherited setting file
one single setting.py with Python logic to change the settings based on context

1. Copy as settings.py settings_production.py

2. IMPORT

# settings.py

DEBUG = True
TEMPLATE_DEBUG = DEBUG

DATABASE_ENGINE = 'postgresql_psycopg2'
DATABASE_NAME = 'devdb'
DATABASE_USER = ''
DATABASE_PASSWORD = ''
DATABASE_PORT = ''

# ...

# settings_production.py

from settings import *

DEBUG = TEMPLATE_DEBUG = False
DATABASE_NAME = 'production'
DATABASE_USER = 'app'
DATABASE_PASSWORD = 'letmein'

override
3. use of Python logic

# settings.py

import socket

if socket.gethostname() == 'my-laptop':
    DEBUG = TEMPLATE_DEBUG = True
else:
    DEBUG = TEMPLATE_DEBUG = False

# ...

IF the name of settings changed:
You can fix this by editing manage.py to change settingsto the name of your module

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "quality.settings_XXX")

Apache + mod_python

http://www.djangoproject.com/r/mod_python/

Basic Configuration

make sure you have Apache installed with the mod_python module activated.

LoadModule python_module /usr/lib/apache2/modules/mod_python.so

Then, edit your Apache configuration file and add a <Location> directive that ties a specific URL path to a specific Django installation.

<Location "/">
    SetHandler python-program
    PythonHandler django.core.handlers.modpython
    SetEnv DJANGO_SETTINGS_MODULE mysite.settings
    PythonDebug Off
</Location>

Make sure to replace mysite.settings with the appropriate DJANGO_SETTINGS_MODULE for your site.

This tells Apache, “Use mod_python for any URL at or under ‘/’, using the Django mod_python handler.” It passes the value of DJANGO_SETTINGS_MODULE so mod_python knows which settings to use.

Note that we’re using the <Location> directive, not the <Directory> directive. The latter is used for pointing at places on your filesystem, whereas <Location> points at places in the URL structure of a Web site. <Directory> would be meaningless here.

Apache likely runs as a different user than your normal login and may have a different path and sys.path. You may need to tell mod_python how to find your project and Django itself.

PythonPath "['/path/to/project', '/path/to/django'] + sys.path"

Running Multiple Django Installations on the Same Apache Instance

to be continued

Running a Development Server with mod_python

Serving Django and Media Files from the Same Apache Instance

Alternative:

Using Django with FastCGI

http://www.djangobook.com/en/2.0/chapter12.html

Scaling

Figure 12-1: a single server Django setup.

However, as traffic increases you’ll quickly run into resource contention between the different pieces of software.

Figure 12-2: Moving the database onto a dedicated server

As far as Django is concerned, the process of separating out the database server is extremely easy: you’ll simply need to change the DATABASE_HOST setting to the IP or DNS name of your database server. It’s probably a good idea to use the IP if at all possible, as relying on DNS for the connection between your Web server and database server isn’t recommended.

Figure 12-3: Separating out the media server.

For sites heavy in static content (photos, videos, etc.), moving to a separate media server is doubly important. Three-server setup: 10 million hits a day

Figure 12-4: A load-balanced, redundant server setup.

Figure 12-5. An example large-scale Django setup.

Performance Tuning

There’s No Such Thing As Too Much RAM

This shouldn’t be too hard; we’ve developed a site with more than half a million newspaper articles, and it took under 2GB of space.

Turn Off Keep-Alive

Use memcached

Of course, selecting memcached does you no good if you don’t actually use it. Chapter 15 is your best friend here: learn how to use Django’s cache framework, and use it everywhere possible. Aggressive, preemptive caching is usually the only thing that will keep a site up under major traffic.
done

done

Daniel

Pages

Sunday, December 23, 2012

Chapter 12: Deploying Django