There are many CDN (Content Delivery Networks) for hosting mainly static content. How do they work? How they handle http requests?
cdn – How Do CDN (Content Delivery Networks) Servers Work?
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At what point is it worth adding a CDN (content delivery network) to your website?
When one of the following occurs:
- You're reaching a large, international audience. Careful analysis of your audience shows that many of them are 100 - 300ms Round Trip Time (RTT) away. You do the math, and discover that a large group of you customers are getting a somewhat slow site, due to TCP/IP's so-so performance on links with high bandwidth delay product.
- You find that you have a lots of requests for mostly static files, i.e. streaming video, audio, PDFs, images etc. In fact, there are so many requests per second that it can't easily be handled by just setting up 2, 3, 4 or more servers dedicated to static file serving.
- You're a tech geek, and you set up a site using Amazon Cloudfront or Cachefly just for the fun of it. Don't feel bad, I have done it too.
I have repeatedly seen articles where SimpleCDN didn't do so great. It is really hard to objectively quantify the performance of the various CDNs, but here is one attempt. Maybe I'm being unfair to SimpleCDN here, but they wouldn't be my first choice.
Amazon Cloudfront is pretty consistenly good ... not great, but cheap and easy to get started with.
Edit: Akamai still seems to be the very best CDN, expensive but so worth it. See SmugMugs recent presentation, slide 7 in the PDF or the more detailed version in the video. I have never worked with Akamai, I have always dismissed them as obviously too expensive for the sites I have worked on. Maybe that is beginning to change, I don't know, but they are trying to lower the barrier to entry to their CDN service.
Putting your assets in a separate domain is a common practice, even Server Fault does it (sstatic.net). I doubt any of your hypotheses are correct, because they would cause problems with too many other legitimate sites. I would contact some of the corporate networks that you're being blocked by (or have the users at those sites do it) and find out why you're being blocked.
Best Answer
Short answer: CDN's take your data and place it on many different servers around the world so that high traffic content can be delivered to the end user as quickly as possible.
Long answer: CDN's distribute your file(s) to multiple edge locations and assign a URI to it. When a request is made the CDN evaluates the location of the request and routes it to the edge location that will provide the lowest latency and best connection speed for the requester. The file is then transferred directly from the edge location's server to the user that requested it.
For more info: High Performance Web Sites: Rule 1 – Make Fewer HTTP Requests