Server load balancers (SLB) split up network traffic from users to multiple computer servers (a cluster). The servers are transparent to the users, who only see one server. This allows servers to be added (scale out) as traffic grows instead of replacing the server with a more powerful and expensive (scale up) multi-processor (SMP) server.
Applications that can be load-balanced include Internet web applications, SAP, Windows Terminal Server, Microsoft Exchange, Microsoft Sharepoint Server, and VMware Virtual Desktop. Some types of software, such as database servers, have their own load balancing solution from the software vendor. One example is Oracle's RAC (Real Application Cluster).
Load balancers can also be used to implement high availability clusters. Additional functions such as SSL acceleration (SSL offloading), web caching, firewall and IPS (Intrusion Prevention System) are often built into the load balancer. These more sophisticated SLBs are sometimes called application delivery controllers (ADC) or application front-end devices (AFE).
