DXC ETag Support

Stuart Blackler

Vote:

Has anyone had any experience in using ETags on the DXC?

We've found the following description (from: http://world.episerver.com/digital-experience-cloud-service/development-considerations/cdn-recommendations/):

The ETag or entity tag is part of HTTP protocol. It is added automatically by IIS and is used for web cache validation. Since you cannot use ETags with DXC Service, it is best to disable or remove them from your solution. See general information on how to disable ETag headers.

To the best of my knowledge, ETags aren't added automatically which leads me to think that the documentation is incorrect in this regard? I'd also like to question what the specific reasons are on why ETags cannot be used?

#173650

Jan 04, 2017 10:50

Vote:

I would guess it's something the CDN service providers within DXC Service and/or Azure Web Apps has issues with.

#174419

Jan 25, 2017 23:19

Petra Liljecrantz

Vote:

I would also like a real actual explaination on the page regarding this, but from what I´ve heard in discussions it´s mainly for reducing trips to the server because if etags are set we will see trips to the server to check if an image has changed even if it´s cached in the CDN.

#179179

Jun 02, 2017 10:14

MartinOttosen

Vote:

It depends what requests you are referring to. Static files uploaded to the asset library should get Etags by default, since we know for a fact when such a resource changes i.e. the only way a static file can change is if you upload a new version. For requests to resources that are composed from arbitrary managed / unmanaged content objects such as a landing page, determining it's e-tag is difficult and currently inefficient to do automatically without re-computing the result every time.

#179190

Jun 02, 2017 13:18

Petra Liljecrantz

Vote:

I was mainly referring to image requests. My answer was based on a discussion and advise we got from Expert Services to remove ETags because it creates unnecessary requests to the backend and the blob storage which impacts performance.

#179191

Jun 02, 2017 13:32

MartinOttosen

Vote:

It seems this recommendation comes from the concern raised here https://developer.yahoo.com/performance/rules.html#etags that etags in a server farms using earlier versions of IIS resulted in etags for the same resource varying from server to server, which obviously is not useful. I'm pretty sure this is not a problem for DXC-S today, but will investigate further.

#179194

Jun 02, 2017 15:39

MartinOttosen

Vote:

Just a quick update. The current recommendations do look outdated, we are going to do some experiments to figure out how e-tags should be generated for what types of resources and update as appropriate. Thanks for bringing this up!

#180256

Jul 04, 2017 12:01