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This module provide easy Content Delivery Network integration for Backdrop CMS.
It alters file URLs, so that files are downloaded from a CDN instead of your
web server.

It provides two modes: "Origin Pull" and "File Conveyor".

In "Origin Pull" mode, only "Origin Pull" CDNs are supported (hence the name).
These are CDNs that only require you to replace the domain name with another
domain name. The CDN will then automatically fetch (pull) the files from your
server (the origin).

In "File Conveyor" mode, this module integrates with the File Conveyor [1]
daemon. This allows for much more advanced setups: files can be processed
(e.g. optimize images like [2], minify CSS with YUI Compressor [3],
minify JS with YUI compressor or Google Closure Compiler [4], and it's easy to
add your own!), before they are synced and your CDN doesn't have to support
Origin Pull, any push method is fine (supported transfer protocols: FTP,
Amazon S3, Rackspace CloudFiles). File Conveyor is flexible enough to be used
with any CDN, thus it enables you to avoid vendor lock-in.

If you're not sure which mode to use, use "Origin Pull". It's easier and more
reliable. Every single common CDN today (2015) supports Origin Pull.

Note: It is essential that you understand the key properties of a CDN, most
importantly the differences between an Origin Pull CDN and a Push CDN. A good
(and compact!) reference is the "Key Properties of a CDN" article [5].

The CDN module aims to do only one thing and do it well: altering URLs to
point to files on CDNs.
However, in later versions, it does as much as possible to make CDN
integration frictionless:
• Any sort of CDN mapping
• optimal Far Future expiration (
- CORS (
- signed URLs prevent abuse
- disabled by default, automatically disabled when in maintenance mode
- requires a CDN or reverse proxy, not Apache/nginx/lighttpd/…!
• Advanced Help integration to guide you (
• DNS prefetching (
• CSS aggregation (
• auto-balance files over multiple CDNs (
• … and many more details that are taken care of automatically

But in some cases, simply altering the URL is not enough, that's where the
AdvAgg module comes in:

If you've ever had any issues with CSS or JS files not behaving as
desired, check out AdvAgg. The "Advanced CSS/JS Aggregation" module solves
all issues that arise from having CSS/JS served from a CDN. Keeping track
of changes to CSS/JS files, smart aggregate names, 404 protection,
on-demand generation, works with private file system, Google CDN
integration, CSS/JS compression, GZIP compression, caching, and smart
bundling are some of the things AdvAgg does. It's also faster then core's
file aggregation.


Supported CDNs

  • Origin Pull mode: any Origin Pull CDN (or alternatively: domains that point
    to your main domain, by using so called "CNAME" DNS records).
  • File Conveyor mode: any Origin Pull CDN and any push CDN that supports FTP.
    Support for other transfer protocols is welcomed and encouraged: your
    patches are welcome! Amazon S3, Amazon CloudFront and Rackspace CloudFiles
    are also supported.


  • Install this module using the official Backdrop CMS instructions at

  • Visit the configuration page under Administration > Configuration >
    Development > CDN (admin/config/development/cdn) to learn about the various

  • Go to your CDN provider's control panel and set up a "CDN instance" (Amazon
    CloudFront calls this a "distribution"). There, you will have to specify
    the origin server (Amazon CloudFront calls this a "custom origin"), which
    is simply the domain name of your Backdrop site.
    The CDN will provide you with a "delivery address", this is the address
    that we'll use to download files from the CDN instead of the Backdrop server.
    Suppose this is
    Be sure to forward query strings from the CDN to the origin! Otherwise image
    style derivatives will not work.
    (It acts like a globally distributed, super fast proxy server.)

    Relevant links:

  • Optionally, you can create a CNAME alias to the delivery address on your
    DNS server. This way, it's not immediately obvious from the links in the
    HTMl that you're using an external service (that's why it's also called a
    vanity domain name).
    However, if you're going to use your CDN in HTTPS mode, then using vanity
    domains will break things (because SSL certificates are bound to domain

  • Enter the domain name (, or the vanity
    domain/CNAME if you used that instead) at admin/settings/cdn/details. If
    you want to support HTTPS transparently, it is recommended to enter it as
    // instead — this is a protocol-relative URL.

  • Visit the Status Report under Administration > Reports > Status
    (admin/reports/status). The CDN module will report its status here.

  • Enable the display of statistics at "admin/config/development/cdn", browse
    your site with your root/admin (user id 1) account. The statistics will
    show which files are served from the CDN!

  • If your site is behind a reverse proxy such as Varnish, so that your stack
    looks like: CDN <-> reverse proxy <-> web server, then you need to take extra
    measures if you want to prevent duplicate content showing up on the CDN. See for details. It's
    possible in this situation to end up with redirect loops; for that reason
    the CDN module adds a debugging header to the 301 redirects it emits in order
    to facilitate troubleshooting.


Additional documentation is located in the Wiki:


Bugs and Feature requests should be reported in the Issue Queue:

Current Maintainers



This project is GPL v2 software. See the LICENSE.txt file in this directory for
complete text.