Content Delivery Network

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A content delivery network ( CDN ), also known as a content distribution network , is a network of regionally distributed servers connected via the Internet with which content - especially large media files - is delivered. A CDN provides scalable storage and delivery capacities and guarantees optimal data throughput even with large load peaks.

CDN nodes are distributed over many locations and often also over many backbones . They work together to inquiries ( requests ) of end users for content ( content ) as economically as possible to use. Individual locations are referred to as PoP ( Point of Presence ) and consist of server clusters.

In the background ( transparent ), the data is stored in the network ( caching ) so that the respective delivery is either as fast as possible ( performance optimization) or uses as little bandwidth as possible (cost optimization), or both at the same time.

Large CDNs maintain thousands of nodes with tens of thousands of servers.


The CDN initially consists of an origin server on which the content provider stores the content to be distributed, a large number of replica servers that hold copies of this content, and a distribution system that distributes the content on the replica servers . To redirect the user requests to each replica server one is request routing system responsible that it is based on various indicators on these servers to it by the accounting system are delivered.

If a client sends a request to the CDN, the request routing system selects a suitable replica server . When making a selection, it obtains key figures about their current load (e.g. CPU load, number of active connections) and about the network connection between client and server (e.g. geographical distance, latency, transfer rate), less often about the identity of the client (e.g. Distinction between standard and premium users) that are made available to him by the accounting system .

After selecting the server, the user request must now be redirected. The most frequently used method for this is DNS- based request routing. Requests from the client are forwarded to a DNS server provided by the CDN, which returns the IP address of the replica server . As an alternative to this, an HTTP status code 302 can also initiate forwarding to another web server.

Selection of CDN providers

Open source software and free service providers

MirrorBrain is free HTTP server software for Linux for operating a CDN.

The contents of free JavaScript , CSS frameworks or free icon sets are offered by various CDN providers for free and permitted hotlinking . Google Hosted Libraries offers well-known libraries such as jQuery , jQuery UI , AngularJS or Dojo Toolkit . Other providers such as Jsdelivr or cdnjs also offer numerous other, smaller libraries. Whereby Jsdelivr also allows grouping into one HTTP request.

See also

Individual evidence