CDN asset URL helpers

This library contains a Rubygem and Django custom templatetag library to do the following:

turn an asset path like

/images/thing.png

into a CDN-pointed URL like

http://cdn.name.com/images/thing.png/{sha1}.png

Rails

Add cdn_helpers to your Gemfile:

gem 'cdn_helpers', :git => 'git@github.com:alphagov/cdn_helpers.git'

In your environments/production.rb:

require 'cdn_helpers'
config.action_controller.asset_host = "http://cdn.url.gov.uk"
config.action_controller.asset_path = CdnHelpers::AssetPath

The gem also make the rake task cdn:css_urls available to you. This is for post-deployment rewriting of URLs within CSS files. It's destructive - it rewrites the files in place - but it doesn't require that the config vars above are set since it leaves URLs as absolute local URLs.

Django

Add cdn_helpers to your requirements.txt:

-e git+ssh://git@github.com/alphagov/cdn_helpers.git#egg=cdn_helpers

in settings.py add cdn_helpers to your list of installed apps:

INSTALLED_APPS = (
    'django.contrib.auth',
    ...
    'cdn_helpers'
)

in your local-development local_settings.py:

APP_DEPLOYMENT_ENV = 'local'   # (disables CDN url generation)
CDN_HOSTS = []

in the appropriate local_settings.py:

APP_DEPLOYMENT_ENV = 'dev'   # (or staging, production)
CDN_HOSTS = ['cdn1', 'cdn2'] # (as appropriate for the environment)
SHARED_PUBLIC_ROOT = "/path/to/shared/assets" # (i.e. where Static's public dir is)

in templates use the asset_url helper:

<img src="{% asset_url "/images/thing.png" %}">
<img src="{% asset_url thing.image.url %}">

The app provides the cdn_css command for manage.py. This uses the Ruby script process_css to do the heavy lifting, but relies on the MEDIA_ROOT and MEDIA_URL settings in settings.py to tell where to look and how to construct the URLs.

Running tests

bundle exec rake spec

PYTHONPATH=py nosetests -w test