NLB and Other Clustering Technologies

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Applies To: Windows Server 2003 with SP1

Q. What is the Difference Between NLB and Server Clusters?

A. A server cluster (MSCS) is a collection of servers that together provide a single, highly available platform for hosting applications. Applications can be failed over to ensure high availability in the event of planned downtime due to maintenance or unplanned downtime due to hardware, Operating System or application failures. Server clusters provide a highly available platform for applications such as SQL Server, Exchange Server data stores, file and print servers, etc. Server clusters are used for stateful applications that rely on some state context from one request to the next.

Network Load Balancing (NLB) clusters dynamically distribute the flow of incoming TCP and UDP traffic among the cluster nodes according to a set of traffic-handling rules. NLB clusters provide a highly available and scalable platform for applications such as IIS, ISA server, etc. NLB is used for stateless applications; i.e. those that do not build any state as a result of a request.

NLB and server clusters compliment each other in complex architectures: NLB is used for load balancing requests between front-end web servers while server clusters provide high availability for backend database access.

NLB and server clusters cannot be used on the same set of servers (see Question Can I use NLB and server clusters on the same set of servers?).

Q. Can I Use NLB and Server Clusters on the Same Set of Servers?

A. No, Microsoft Server clusters (MSCS) and Network Load Balancing (NLB) are not supported on the same set of nodes. Both Server clusters and Network Load Balancing clusters control and configure network adapters. Since they are not aware of each other, configuring one can interfere with the other.