HTTP: The Definitive Guide

Making Web Sites Reliable

There are several times during which web sites commonly break:

• Server downtime

• Traffic spikes: suddenly everyone wants to see a particular news broadcast or rush to a sale. Sudden spikes can overload a web server, slowing it down or stopping it completely.

• Network outages or losses

This section presents some ways of anticipating and dealing with these common problems.

Mirrored Server Farms

A server farm is a bank of identically configured web servers that can cover for each other. The content on each server in the farm can be mirrored, so that if one has a problem, another can fill in.

Often, mirrored servers follow a hierarchical relationship. One server might act as the “content authority”—the server that contains the original content (perhaps a server to which the content authors post). This server is called the master origin server . The mirrored servers that receive content from the master origin server are called replica origin servers . One simple way to deploy a server farm is to use a network switch to distribute requests to the servers. The IP address for each of the web sites hosted on the servers is the IP address of the switch.

In the mirrored server farm shown in Figure 18-6, the master origin server is responsible for sending content to the replica origin servers. To the outside world, the IP address for this content is the IP address of the switch. The switch is responsible for sending requests to the servers.

Figure 18-6. Mirrored server ...