The mail goals of Load Balancer is provide high availability, load balancing with simple configuration, and cheap hardware equipment. Also, Load Balancer aims to be full extendable, and fully configurable without sacrifing ease of user & configuration.

I understand Load Balancing as the ability of balance request between servers, so the workload is splitted across the servers, giving a more uniform response time.

I understand High Availability as the ability of serve requests without any interruption in the service.

Today, we need reliable, high available systems, to attend the requests done by the clients. There are lots of tools (hardware and software) to do this work, but usually there are too expensive or too complex to use them in a medium-sized site. Also, this tools usually require some complex configuration, and special network topologies. Another drawback for this services is the lack of protocol-specific details that they have (usually, some 'known' services (HTTP, FTP, etc) are fully supported, but another ones (e.g. propietary protocols, or some less known) are poor supported, or none. Load Balancer is fully extensible in the plugin way; you can create your own proxies for your protocols (allowing these to be balanced, high available ones) or use the plugins that comes with Load Balancer.

Also, Load Balancer allows you to have clusters of servers so you can split traffic using the client request (e.g. dealing with http traffic, you can create a cluster to server cgi-bin scripts, another cluster to server html pages, and another one to serve images), isolating load from them. Load Balancer support IP filter address, so you can deny access to a range of clients, or balance them into another cluster (e.g. you can balance by geographical distribution).

Basically, Load Balancer works like a proxy does, but it has some code to manage the status of the clusters in server farm, to balance the request between the servers, and to do the proxy work for the client to the server. Load Balancer doesn't know nothing about the protocols (unless you use / program a plugin that manages thet protocol in a smart way) so the Load Balancer is fully transparent to the client. In the next section I talk about the internal details, and the plugin configuration.