From Nagios Wiki

[edit] Intro

Application Load Balancing is when you have an IP application service, such as http (web) and you need to spread it across multiple servers to handle a large load and have redundancy.

[edit] Load Balancers

There are numerous types and manufacturers of load balancers.

[edit] Types of Load Balancing

• Standard Application Load Balancing
• Definitions and configurations of DSR