Load balancing

Updated: October 4, 2007

Applies To: Windows Server 2008, Windows Server 2008 R2

Load balancing software typically works with the clustering software to manage the server workload within the cluster so that it is evenly distributed among the nodes. It monitors the operation of each node and divides the streaming workload according to a predetermined formula or algorithm. It also ensures that, even though the stream may originate from any of several different nodes, the content is represented by a single IP address.

There are two primary load balancing strategies:

  • Hardware-based load balancing. Also known as reverse proxy, this method relies on a proxy server that is placed in the network between the server cluster and the clients. The reverse proxy server receives stream requests from the client and either redirects the client to the appropriate server or proxies content from that server to the client. To avoid creating a single point of failure, you can use two or more reverse proxy machines in parallel.

  • Software-based load balancing. Software-based load balancing features such as Network Load Balancing (NLB) assign a percentage of the total server load to each node in the cluster. The load balancing software runs on each node of the cluster and calculates which node will be the next to accept a new request based on each server's percentage of the total workload. The advantages of this load balancing method include speed, configurability, reliability, and reduced cost. NLB uses a fully distributed filtering algorithm. Every second, each node in the cluster emits a "heartbeat" signal which contains information about its status. NLB monitors these signals for changes in the cluster status and changes the service request distribution appropriately.

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