.. _remote_storages:

Remote Storages
---------------

In some cases it's useful to use a CDN_ for serving static files such as
those generated by Django Compressor. Due to the way Django Compressor
processes files, it requires the files to be processed (in the
``{% compress %}`` block) to be available in a local file system cache.

Django Compressor provides hooks to automatically have compressed files
pushed to a remote storage backend. Simply set the storage backend
that saves the result to a remote service (see
:attr:`~django.conf.settings.COMPRESS_STORAGE`).

django-storages
^^^^^^^^^^^^^^^

So assuming your CDN is `Amazon S3`_, you can use the boto3_ storage backend
from the 3rd party app `django-storages`_. Some required settings are::

    AWS_ACCESS_KEY_ID = 'XXXXXXXXXXXXXXXXXXXXX'
    AWS_SECRET_ACCESS_KEY = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
    AWS_STORAGE_BUCKET_NAME = 'compressor-test'

Next, you need to specify the new CDN base URL and update the URLs to the
files in your templates which you want to compress::

    COMPRESS_URL = "http://compressor-test.s3.amazonaws.com/"

.. note::

    For staticfiles just set ``STATIC_URL = COMPRESS_URL``

The storage backend to save the compressed files needs to be changed, too::

    COMPRESS_STORAGE = 'storages.backends.s3boto3.S3Boto3Storage'

Using staticfiles
^^^^^^^^^^^^^^^^^

If you are using Django's staticfiles_ contrib app, you'll need to use a
temporary filesystem cache for Django Compressor to know which files to
compress. Since staticfiles provides a management command to collect static
files from various locations which uses a storage backend, this is where both
apps can be integrated.

#. Make sure the :attr:`~django.conf.settings.COMPRESS_ROOT` and STATIC_ROOT_
   settings are equal since both apps need to look at the same directories
   when doing their job.

#. You need to create a subclass of the remote storage backend you want
   to use; below is an example of the boto3 S3 storage backend from
   django-storages_::

    from django.core.files.storage import get_storage_class
    from storages.backends.s3boto3 import S3Boto3Storage

    class CachedS3Boto3Storage(S3Boto3Storage):
        """
        S3 storage backend that saves the files locally, too.
        """
        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)
            self.local_storage = get_storage_class(
                "compressor.storage.CompressorFileStorage")()

        def save(self, name, content):
            self.local_storage.save(name, content)
            super().save(name, self.local_storage._open(name))
            return name

#. Set your :attr:`~django.conf.settings.COMPRESS_STORAGE`, STATICFILES_STORAGE_
   and :attr:`~django.conf.settings.COMPRESS_OFFLINE_MANIFEST_STORAGE` settings 
   to the dotted path of your custom cached storage backend, e.g.
   ``'mysite.storage.CachedS3Boto3Storage'``.

#. To have Django correctly render the URLs to your static files, set the
   STATIC_URL_ setting to the same value as
   :attr:`~django.conf.settings.COMPRESS_URL` (e.g.
   ``"http://compressor-test.s3.amazonaws.com/"``).

In the end it might look like this::

    STATIC_ROOT = '/path/to/staticfiles'
    COMPRESS_ROOT = STATIC_ROOT
    STATICFILES_STORAGE = 'mysite.storage.CachedS3BotoStorage'
    COMPRESS_STORAGE = STATICFILES_STORAGE
    COMPRESS_OFFLINE_MANIFEST_STORAGE = STATICFILES_STORAGE
    STATIC_URL = 'https://compressor-test.s3.amazonaws.com/'
    COMPRESS_URL = STATIC_URL

.. _CDN: http://en.wikipedia.org/wiki/Content_delivery_network
.. _Amazon S3: https://s3.amazonaws.com/
.. _boto3: http://boto3.readthedocs.io/
.. _django-storages: http://github.com/jschneier/django-storages
.. _staticfiles: http://docs.djangoproject.com/en/dev/howto/static-files/
.. _STATIC_ROOT: http://docs.djangoproject.com/en/dev/ref/settings/#static-root
.. _STATIC_URL: http://docs.djangoproject.com/en/dev/ref/settings/#static-url
.. _STATICFILES_STORAGE: http://docs.djangoproject.com/en/dev/ref/contrib/staticfiles/#staticfiles-storage