Overview of ARR in ECN and CDN

Updated: November 5, 2009

Applies To: Windows 7, Windows Server 2008, Windows Server 2008 R2, Windows Vista

Application Request Routing (ARR) is a proxy-based routing module that uses HTTP headers, server variables, and load balance algorithms to determine how to forward HTTP requests to content servers. ARR uses the URL rewrite rules that are automatically created when you define a server farm to inspect incoming requests to make routing decisions. In a content delivery network (CDN) or edge caching network (ECN), these rules cannot work as written because the cache nodes are tiered. If there is a cache miss at the child cache nodes, the parent cache nodes are unable to find the origin servers. To prevent this issue, you can map the origin servers on the child cache nodes before requests are routed to the parent cache nodes. With the origin server map and advanced URL rewrite rules, requests from a cache miss are routed to the parent cache node with the host name that matches the origin server.

For more information about how to use ARR in CDN/ECN environments, see ARR Tasks for ECNs and CDNs.

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