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Content-based Request Distribution

Content-based request distribution is a technique employed in cluster-based network servers, where the front-end takes into account the service/content requested when deciding which back-end node should serve a given request. In contrast, the purely load-based schemes like weighted round-robin (WRR) used in commercial high performance cluster servers [15,8] distribute incoming requests in a round-robin fashion, weighted by some measure of load on the different back-end nodes.

The potential advantages of content-based request distribution are: (1) increased performance due to improved hit rates in the back-end's main memory caches, (2) increased secondary storage scalability due to the ability to partition the server's database over the different back-end nodes, and (3) the ability to employ back-end nodes that are specialized for certain types of requests (e.g., audio and video).

With content-based request distribution, the front-end must establish the TCP connection with the client prior to assigning the connection to a back-end node, since the nature and the target1 of the client's request influences the assignment. Thus, a mechanism is required that allows a chosen back-end node to serve a request on the TCP connection established by the front-end. For reasons of performance, security, and interoperability, it is desirable that this mechanism be transparent to the client. We will discuss mechanisms for this purpose in Section 3.


next up previous
Next: Locality-aware request distribution Up: Background Previous: HTTP/1.1 persistent connections
Peter Druschel
1999-04-27