Adds information about the new ability to use a CDN for course assets, (

#765)

and how to configure what the CDN information is so courses specify the
right URLs.
(cherry picked from commit f00209a)

en_us/install_operations/source/configuration/index.rst

@@ -29,3 +29,4 @@ configuration options.
    enable_timed_exams
    youtube_api
    install_xblock
+   static_replace/cdn

en_us/install_operations/source/configuration/static_replace/cdn.rst

@@ -0,0 +1,72 @@
+.. _Enabling a CDN for Course Assets:
+
+######################################
+Enabling a CDN for Course Assets
+######################################
+
+By default, all course assets are served directly from your Open edX instance.
+For courses with large enrollments, or courses with large assets, such as high-
+quality images, PDFs, or video files, this can increase not only the load on
+the instance but also the time it takes for learners to load the courses on
+their computers and mobile devices.
+
+You can configure your Open edX instance to serve assets from a content
+delivery network (CDN) instead. Using a CDN offloads the work required to
+deliver assets from your Open edX instance.
+
+.. note:: Whether you need a CDN depends on the type, and amount, of content
+  in your courses. Not all installations need a CDN for their course assets.
+
+
+.. contents::
+   :local:
+   :depth: 1
+
+***************
+Overview
+***************
+
+A CDN, or content delivery network, is a service that places servers all around
+the world, and keeps copies of content on those servers. Instead of serving
+files from one location, a CDN serves them from whichever server is closest to
+the end user. This results in faster download speeds and, ultimately, faster
+page loads.
+
+********************************
+Guidelines for CDN Configuration
+********************************
+
+When you configure a CDN for use with your Open edX instance, you should
+identify your Open edX instance as the origin server.
+
+Choose the cache expiration carefully: you want content to be cached long
+enough to keep the load on your Open edX instance low, but not so long that
+changes made to course assets are not realized within a reasonable amount of
+time. As a starting point, edX recommends a cache expiration period of one
+hour.
+
+**********************
+Enable the CDN
+**********************
+
+After you configure your CDN, follow these steps.
+
+#. Sign in to the Django administration console for your base URL. For example,
+   ``http://{your_URL}/admin``.
+
+#. In the **Static_Replace** section, next to **Asset base url configs**,
+   select **Add**.
+
+#. Select **Enabled**.
+
+#. Enter the hostname for your CDN provider.
+
+   For example, if you were using CloudFront, this would look something like
+   ``d37djvu3ytnwxt.cloudfront.net``.
+
+   Be sure not to include the scheme (``http://`` or ``https://``) when you
+   specify the hostname.
+
+#. Select **Save**.
+
+.. include:: ../../../../links/links.rst