HTTP ETag reproduction

Having recently discovered problems relating to the HTTP ETag and our CDN I've tried to capture some in Fiddler for well known sites. However it appears that whatever combination of browser / w开发者_开发问答ebsite I use I'm not seeing any pass by.

Is there any reason for this? Can you suggest a combination in which I can see them? Perhaps they're not widely used anymore?

They are definitely widely used, I've used it myself often. The most common usecase is conditional requests (always check if there's new content, but only send the content back from the server if it has changed).

However, Last-Modified can also do this instead and it's not needed if you don't force the browser to always check for new content (no must-revalidate).

The reason your CDN isn't using them is one of the following:

• They are using Last-Modified instead
• They don't force a revalidation and set an expiry time well in the future
• They couldn't determine a ETag for a particular piece of content
• Misconfiguration