Has anyone successfully configured Azure CDN for HTTP compression using their hosted web role? We are having trouble compressing HTTP content at the Azure edge servers. The CDN is only caching the uncompressed version of the content.
If we hit our resource link (webresource.axd) from a non-Azure approach it compresses via gzip (using the xxxx.cloudapp.net/cdn/webresource.axd) as expected. However, as soon as we point our resource link to Azure CDN (xxxx.vo.msecnd.net), the content is served up uncompressed, despite the browser telling the Azure CDN it accepts gzip.
I posted this same issue to Azure Forums, but nobody has responded as of yet.
While troubleshooting the problem, it appears that the Azure CDN is stripping out the Accept-Encoding HTTP header. Just curious if others have had this same issue.
Azure CDN Best Practices states...
How does the Windows Azure CDN work with compressed content?
The Windows Azure CDN will not modify (or add) compression to your objects. The Windows Azure CDN respects whatever compression is provided by the origin based on the "Accept-Encoding" header. As of 1.4, Azure Storage does not support compression. If you are using hosted-service object delivery, you can configure IIS to return compressed objects.
What we are seeing is that the CDN is not respecting the origin Accept-Encoding, it's being stripped away.
It was discovered thru trial and error that Azure CDN has a current limitation that it won't pass the Accept-Encoding HTTP header unless it finds a QueryString parameter containing a compressable filename type (.js, .cs) or you are requesting a file by its original name (jquery.js, site.css, etc.).
What this means is that if you are using an AXD resource handler (WebResource.axd, etc.), the HTTP compression will not be performed. The Azure CDN will only pass the Accept-Encoding if you append a QueryString parameter with a .cs or .js extension.
We are using a custom AXD resource handler, so this was easy for us to implement. We just applied &group=core.js and &group=core.css for our combined minified resources and the compression worked as expected. It's unfortunate this doesn't exist in the current Azure CDN documentation.
In short, we had to transform our URIs from this:
https://xxxx.vo.msecnd.net/resourceManager.axd?token=HL80vX5hf3lIAAA
to this:
https://xxxx.vo.msecnd.net/resourceManager.axd?token=HL80vX5hf3lIAAA&group=core.js
Once the Azure CDN sees the .js in the querystring, it will return the compressed version of the resource.
Hope this helps someone else using web resources (AXDs) served up via the Azure CDN.