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What exactly is a Content Delivery Network (CDN), how does it work, and why would I want to use one for my web site? Which are the well-known CDNs out there?

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We are working on [improving performance of OXID eShops][1] by primarily using NGINX to host the static content and Apache for the application itself. Content Delivery Network doesn't yet seem to make sense for us, but we'll be exploring our options here as well. The costs for the Microsoft CDN above seem quite reasonable. Does anyone have examples of other more lucrative offers? Thanks for the thread... Ashant [1]: oxid-blog.euroblaze.de/shop-performance/… –  Ashant Chalasani Feb 10 '11 at 20:49
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4 Answers

up vote 9 down vote accepted

Definition

Wikipedia says it well:

A content delivery network or content distribution network (CDN) is a system of computers containing copies of data, placed at various points in a network so as to maximize bandwidth for access to the data from clients throughout the network. A client accesses a copy of the data near to the client, as opposed to all clients accessing the same central server, so as to avoid bottleneck near that server.

Content types include web objects, downloadable objects (media files, software, documents), applications, real time media streams, and other components of internet delivery (DNS, routes, and database queries)

Benefits

Common CDNs

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Hey, could you please tell me: if I decide to use Amazon CloudFront, what is the URL of my images going to be like? www.mydomain.com/image.gif or an Amazon CDN domain like www.ama-cdn.com/... (or whatever domains Amazon uses)? –  Šime Vidas Nov 23 '10 at 23:29
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When someone open your site, content are arranged in a queue. Untill or unless 1st component is delievered other component cant be. So the overall loading speed of your site is increased. If you use some CDN then requests can be processed parrelaly. So the overall speed increases.

You can use your own site as CDN from yourself by creating subdomain.

Better to use google or wordpress for static contents. Their DNS resolving time is very less

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All modern browsers support multiple parallel downloads; older ones support 2 pr hostname and newer one ~6 per hostname, see browserscope.org . You cannot make a CDN by just moving static assets to a subdomain. To replicate the functionality of a CDN you need to have servers in many places around the globe. –  Jesper Mortensen Sep 22 '10 at 11:01
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Microsoft is also running Windows Azure CDN and they recently released their pricing structure for it as:

“The following three billing meters and rates will apply for the CDN:

•$0.15 per GB for data transfers from European and North American locations
•$0.20 per GB for data transfers from other locations
•$0.01 per 10,000 transactions”
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Content Delivery Networks host copies of your content and serve it to your visitors from a server that's close to them. For example, if your images are served through a CDN, a visitor to your site transparently downloads the images from the CDN's server instead of yours.

The two biggest reasons for using a CDN are reducing traffic/bandwidth on your server, and increasing delivery speed. A CDN acts as a cache: it downloads your content from your server once, and then delivers it to all visitors from its own servers instead of yours. A CDN will also have a large number of servers located around the globe, so they will be able to serve content to most visitors from a closer location than you could, and thus get it there faster.

The two biggest CDNs I'm aware of are Akamai and Limelight.

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