Proxying for Load Balancing

You can use multiple proxy servers within an organization to balance the network load among web servers. This model takes advantage of the caching features of the proxy server to create a server pool for load balancing. In this case, the proxy servers can be on either side of the firewall. If you have a web server that receives a high number of requests per day, you could use proxy servers to take the load off the web server and make the network access more efficient.

The proxy servers act as go-betweens for client requests to the real server. The proxy servers cache the requested documents. If you have more than one proxy server, DNS can route the requests randomly using a “round-robin” selection of their IP addresses. The client uses the same URL each time, but the route the request takes might go through a different proxy each time.

The advantage of using multiple proxies to handle requests to one heavily used content server is that the server can handle a heavier load, and more efficiently than it could alone. After an initial start-up period in which the proxies retrieve documents from the content server for the first time, the number of requests to the content server can drop dramatically.

Only CGI requests and occasional new requests must go all the way to the content server. The rest can be handled by a proxy. For example, suppose that 90% of the requests to your server are not CGI requests, which means they can be cached, and that your content server receives 2 million hits per day. In this situation, if you connect three reverse proxies and each of them handles 2 million hits per day, about 6 million hits per day would then be possible. The 10% of requests that reach the content server could add up to about 200,000 hits from each proxy per day, or only 600,000 total, which is far more efficient. The number of hits could increase from approximately 2 million to 6 million, and the load on the content server could decrease correspondingly from 2 million to 600,000. Your actual results would depend upon your situation.

Figure 14–5 Proxy Used for Load Balancing