Network Load Balancing Overview

Network Load Balancing clusters distribute client connections over multiple servers, providing scalability and high availability for client requests for TCP/IP-based services and applications.

The heart of Network Load Balancing is the driver Wlbs.sys, which is loaded into each member server, or host, in the cluster. Wlbs.sys includes the statistical mapping algorithm that the cluster hosts collectively use to determine which host handles each incoming request.

Load-balanced applications need to carefully manage state on the server. State that is persistent across multiple requests or that is shared among clients needs to be shared in locations that are transparently accessible from all cluster hosts. Updates to state that is shared among the hosts needs to be synchronized — for example, by using a back-end database server.

Network Load Balancing provides the following:

• Load balancing
  Load balancing is static (unless the cluster set changes). The port rules that you create for the cluster's hosts specify the division of the incoming client connections.

• High availability
  If a host fails, the cluster detects the failure and redistributes subsequent client requests to hosts that are still viable members of the cluster. Any client connections that were open when the host failed are ended. On retry, the client connection is routed to a viable host. The downtime for client connections is less than 10 seconds.

• Scalability
  Network Load Balancing accomplishes scalability by allowing you to add as many as 32 hosts to the cluster. You can add hosts without shutting down the cluster.