Abstract

We present a scalable architecture for content-aware request distribution in Web server clusters. In this architecture, a level-4 switch acts as the point of contact for the server on the Internet and distributes the incoming requests to a number of back-end nodes. The switch does not perform any content-based distribution. This function is performed by each of the back-end nodes, which may forward the incoming request to another back-end based on the requested content.

In terms of scalability, this architecture compares favorably to existing approaches where a front-end node performs content-based distribution. In our architecture, the expensive operations of TCP connection establishment and handoff are distributed among the back-ends, rather than being centralized in the front-end node. Only a minimal additional latency penalty is paid for much improved scalability.

We have implemented this new architecture, and we demonstrate its superior scalability by comparing it to a system that performs content-aware distribution in the front-end, both under synthetic and trace-driven workloads.