The concept of a real server in content switching is very important. While the name might give the impression that the definition must be a traditional server of some flavor, this is not necessarily always the case. In the instances of server load balancing as an application, the real server definitions are typically normal Web or application servers. In the instance of cache redirection, the real servers will be the caches rather than a Web server, and in firewall load balancing the real servers merely represent the path through the firewalled network. From this, it's easy to see that a real server is merely the definition of a resource, typically identified by a unique real server IP address, or RIP. In server load balancing terms, an RIP is the actual IP address the content switch will use when performing the translation required to send a client request to an object server. In application redirection, the real server enables the content switch to resolve a MAC address that must be used when the translation takes place at Layer 2 only. Real servers are traditionally associated to a group. This means that load balancing is typically done to a group of real servers rather than an individual server. This allows administrators to bring servers into and out of a group without impacting the application. The more servers in a group, the more the load will be distributed. Load distribution is dependent on load balancing metrics discussed in Chapter 5, Basic Server Load Balancing . |