django-downloadview/docs/optimizations/nginx.txt

#####
Nginx
#####

If you serve Django behind Nginx, then you can delegate the file streaming
to Nginx and get increased performance:

* lower resources used by Python/Django workers ;
* faster download.

See `Nginx X-accel documentation`_ for details.


*****************
Known limitations
*****************

* Nginx needs access to the resource by URL (proxy) or path (location).
* Thus :class:`~django_downloadview.files.VirtualFile` and any generated files
  cannot be streamed by Nginx.


************
Given a view
************

Let's consider the following view:

.. literalinclude:: /../demo/demoproject/nginx/views.py
   :language: python
   :lines: 1-6, 8-16

What is important here is that the files will have an ``url`` property
implemented by storage. Let's setup an optimization rule based on that URL.

.. note::

   It is generally easier to setup rules based on URL rather than based on
   name in filesystem. This is because path is generally relative to storage,
   whereas URL usually contains some storage identifier, i.e. it is easier to
   target a specific location by URL rather than by filesystem name.


********************************
Setup XAccelRedirect middlewares
********************************

Make sure ``django_downloadview.SmartDownloadMiddleware`` is in
``MIDDLEWARE_CLASSES`` of your `Django` settings.

Example:

.. literalinclude:: /../demo/demoproject/settings.py
   :language: python
   :lines: 63-70

Then set ``django_downloadview.nginx.XAccelRedirectMiddleware`` as
``DOWNLOADVIEW_BACKEND``:

.. literalinclude:: /../demo/demoproject/settings.py
   :language: python
   :lines: 76

Then register as many ``DOWNLOADVIEW_RULES`` as you wish:

.. literalinclude:: /../demo/demoproject/settings.py
   :language: python
   :lines: 84-89

Each item in ``DOWNLOADVIEW_RULES`` is a dictionary of keyword arguments passed
to the middleware factory. In the example above, we capture responses by
``source_url`` and convert them to internal redirects to ``destination_url``.

.. autoclass:: django_downloadview.nginx.middlewares.XAccelRedirectMiddleware
   :members:
   :inherited-members:
   :undoc-members:
   :show-inheritance:
   :member-order: bysource


**********************************************
Per-view setup with x_accel_redirect decorator
**********************************************

Middlewares should be enough for most use cases, but you may want per-view
configuration. For `nginx`, there is ``x_accel_redirect``:

.. autofunction:: django_downloadview.nginx.decorators.x_accel_redirect

As an example:

.. literalinclude:: /../demo/demoproject/nginx/views.py
   :language: python
   :lines: 1-7, 17-


*******************************************
Test responses with assert_x_accel_redirect
*******************************************

Use :func:`~django_downloadview.nginx.decorators.assert_x_accel_redirect`
function as a shortcut in your tests.

.. literalinclude:: /../demo/demoproject/nginx/tests.py
   :language: python

.. autofunction:: django_downloadview.nginx.tests.assert_x_accel_redirect

The tests above assert the `Django` part is OK. Now let's configure `nginx`.


***********
Setup Nginx
***********

See `Nginx X-accel documentation`_ for details.

Here is what you could have in :file:`/etc/nginx/sites-available/default`:

.. code-block:: nginx

   charset utf-8;

   # Django-powered service.
   upstream frontend {
       server 127.0.0.1:8000 fail_timeout=0;
   }

   server {
       listen 80 default;

       # File-download proxy.
       #
       # Will serve /var/www/files/myfile.tar.gz when passed URI
       # like /optimized-download/myfile.tar.gz
       #
       # See http://wiki.nginx.org/X-accel
       # and https://django-downloadview.readthedocs.io
       #
       location /proxied-download {
           internal;
           # Location to files on disk.
           alias /var/www/files/;
       } 

       # Proxy to Django-powered frontend.
       location / {
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           proxy_set_header Host $http_host;
           proxy_redirect off;
           proxy_pass http://frontend;
       }
   }

... where specific configuration is the ``location /optimized-download``
section.  

.. note::

   ``/proxied-download`` has the ``internal`` flag, so this location is not
   available for the client, i.e. users are not able to download files via
   ``/optimized-download/<filename>``.


*********************************************
Assert everything goes fine with healthchecks
*********************************************

:doc:`Healthchecks </healthchecks>` are the best way to check the complete
setup.


*************
Common issues
*************

``Unknown charset "utf-8" to override``
=======================================

Add ``charset utf-8;`` in your nginx configuration file.

``open() "path/to/something" failed (2: No such file or directory)``
====================================================================

Check your ``settings.NGINX_DOWNLOAD_MIDDLEWARE_MEDIA_ROOT`` in Django
configuration VS ``alias`` in nginx configuration: in a standard configuration,
they should be equal.


.. rubric:: References

.. target-notes::

.. _`Nginx X-accel documentation`: http://wiki.nginx.org/X-accel