Network Dispatcher: a connection router for scalable Internet services

Network Dispatcher (ND) is a TCP connection router that supports load sharing across several TCP servers. Prototypes of Network Dispatcher were used to support several large scale high-load Web sites. Network Dispatcher provides a fast IP packet-forwarding kernel-extension to the TCP IP stack. Load sharing is supported by a user-level manager process that monitors the load on the servers and controls the connection allocation algorithm in the kernel extension. This paper describes the design of Network Dispatcher, outlines Network Dispatcher's performance in the context of http traffic, and presents several of its features including high-availability, support for WANs, and client affinity.