Load balancing a cluster of web servers: using distributed packet rewriting

We present and evaluate an implementation of a prototype scalable web server consisting of a load-balanced cluster of hosts that collectively accept and service TCP connections. The host IP addresses are advertised using round robin DNS (RR-DNS) technique, allowing any host to receive requests from any client. Once a client attempts to establish a TCP connection with one of the hosts, a decision is made as to whether or not the connection should be redirected to a different host-namely, the host with the lowest number of established connections. We use the low-overhead Distributed Packet Rewriting (DPR) technique to redirect TCP connections. In our prototype, each host keeps information about the remaining hosts in the system. Load information is maintained using periodic multicast amongst the cluster hosts. Performance measurements suggest that our prototype outperforms both pure RR-DNS and the stateless DPR solutions.