Ok, so 2 of my previous questions got locked (even though damoncloudflare tried to help and answer) because it's off-topic and it's too broad and it's asking too many questions in a single question.

How am I supposed to ask a question how various CDNs handle a specific HTTP header? I need to find out from people with experience and/or knowledge how Akamai, Cloudflare, Edgecast and Cloudfront handle Vary: User-Agent header.

It is about a website that I control. It is about 1 very specific http header and 4 very specific CDN services. http://webmasters.stackexchange.com has CDN tag with 110 questions tagged so it, so it's not offtopic here. So what magic combination of words should I use for this question to be allowed?

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Here is how I would ask you question in such a way that:

  • It is clearly about your website.
  • It asks a single question.
  • It is answerable and not open ended.
  • It isn't too broad

If content delivery networks honor the 'Vary: User-Agent' header, does it effect performance?

We want to change the Vary header that our website returns to:

Vary: User-Agent

Our page can be different for different browsers because we have optimizations in place for older browsers. We want to make sure that our content delivery network (CDN) doesn't give a page that was generated for one browser to another. For example our html5 pages don't work in Internet Explorer before version 7.

The way to do this appears to be setting the Vary header to inform CDNs and proxies that the page can be different for different user agents.

We are worried that this will not work with our CDN. If the CDN honors the header, wouldn't it greatly reduce its effectiveness? The CDN would have to store many more copies of the page and the cache hit ratio would be much lower.

Here is a summary of the major changes.

  • Starting a question with "How do" isn't good form. It makes the question open ended and broad. It is hard to answer many "How do" questions in a few paragraphs. "How do" questions also often have multiple "correct" answers. Questions that start with "Do" or "Is" are usually much narrower in scope.
  • Leave out all the stuff about Accept-Encoding. It isn't relevant to your main concern and makes the question too broad.
  • Leave out the question about whether the CDNs store lots of copies of a page. Only one question per post is acceptable. I rephrased this into an assumption about the main question.
  • Leave out the request for information about specific CDN implementations. Open ended requests like this are not allowed on this site.
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I don't understand why NOT asking about specific implementations of specific CDNs makes it LESS broad.

Your modified question of If content delivery networks honor the 'Vary: User-Agent' header, does it effect performance? is different from the information I'm trying to get. There's no doubt that IF CDN honors this header it will affect performance. The question is HOW CDNs, the ones I use specifically (but others for reference would be good too) react to this header.

Answers like these would've been perfectly acceptable and very far from "too broad": (not necessarily correct, just as an example)

  • Akamai does not cache at all.
  • Edgecast honors full user-agent string.
  • CloudFlare groups by vendor and major version.

This could've been a go-to reference for people looking for canonical information on this specific topic.

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  • You could ask about a specific CDN, but asking for a list of CDNs along with how they handle it is off-topic. We don't accept "big list" questions because they mess with the voting system and they attract spam. – Stephen Ostermiller Feb 12 '14 at 15:31
  • @StephenOstermiller Well, my 2nd question was not a "big list". It was 4 specific CDNs that I use. And isn't that what community wiki checkbox is for? To allow people to add, expand and update answers? – Mxx Feb 12 '14 at 17:15

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