UGN articles UGN articlesA cluster is a group of computers that work together to run a common set of applications and to give the impression of a single system to the client and application. The goal of clustering is to enhance the availability of services and the scalability, reliability, and manageability of operating systems that provide the services. Exchange Server 2003 can be installed in a clustered environment, which ensures the integrity of services and their availability to the client computers. In a cluster, if one node is offline due to any reason, the other cluster-nodes can be used to provide services to the client computers. Microsoft provides administrators with two types of clustering technologies: Network Load Balancing and Microsoft Cluster Service. The goal of both these techniques is to make sure that the services are provided to client computers uninterruptedly even if a cluster-node fails or becomes offline. However, this common goal is achieved by both these techniques in different ways.
Network Load Balancing: It is the oldest clustering technology, and is available with all versions of Windows Server 2003. Its primary goal is to load-balance by distributing TCP/IP traffic among each node in a cluster. It runs as a driver in Microsoft Windows and distributes incoming requests across each node in the cluster. It is configured through Network Load Balancing Manager, which is found in the Administrative Tools program menu. A cluster using Network Load Balancing can have a maximum of 32 nodes. When a cluster is prepared using Network Load Balancing, all the client computers access it by using a single IP address, as the cluster is seen as a single resource. However, each cluster-node contains an individual copy of applications.
Network Load Balancing requires no special hardware to support a multiple-node cluster. A cluster using Network Load Balancing can have servers containing more than one network adapter in each, and multiple Windows Server operating systems. By allowing servers to use multiple network cards, it increases the fault-tolerance of individual servers and allows communication between cluster-nodes in the Unicast mode. In Network Load Balancing, each node in the cluster emits network packets, called heartbeat, every second. In the event of a node-failure, the heartbeat stops. Then, by default, after five seconds, the remaining nodes start the process of convergence in which the incoming client requests are redirected to other nodes. With these advantages, this technique has a few disadvantages as well. It is unable to detect when a specific service is offline on a functioning server. It detects only when the server stops responding. In addition to this, Network Load Balancing works only with TCP/IP.
Microsoft Cluster Service: Like Network Load Balancing, Microsoft Cluster Service uses heartbeats to monitor the status of cluster-nodes. It is different from Network Load Balancing in the sense that it is sensitive to the application services, which means that it can immediately detect whether or not a specific service is running on a node. This allows failover immediately when a service fails, not when a server fails responding. It requires Windows Server 2003 Enterprise Edition or Windows Server 2003 Datacenter Edition. It supports up to eight-node clusters with the condition that beyond two nodes, each node must be running the same version of the operating system. Being sensitive to the applications as well as the services running on a node, it is more suitable than Network Load Balancing for database applications such as SQL Server and Exchange Server.
When Microsoft Cluster Service is used with Exchange Server 2003, it is recommended to use the active/passive model because this model supports only two nodes in an Exchange Server 2003 cluster. The active/passive clusters are better scalable, as they can support up to eight nodes in a cluster. Before installing Exchange Server 2003 in a cluster, an administrator must prepare Windows Server 2003 cluster servers. After that, he must update the Active Directory by running the FORESTPREP and DOMAINPREP utilities. After performing these two actions, he should install Exchange Server 2003 on each node of the cluster one-by-one.
Server nodes running Microsoft Cluster Service must be the members of a domain. They require two or more network adapters. They can be either domain controllers or member servers, but they must belong to the same domain. In addition to this, Microsoft Cluster Service requires a minimum of two Domain Name System (DNS) servers in a domain.
An administrator can create a Windows Server 2003 cluster in the following way:
1. In the Cluster Administrator window, click the File menu > New > Cluster.
2. In the New Server Cluster Wizard window, click the Next button.
3. In the New Server Cluster Wizard window, select the domain, and type the cluster name in the Domain and Cluster Name sections, respectively, and click the Next button.
4. In the New Server Cluster Wizard window, enter the name of the server in the Computer Name section, and click the Next button.
5. In the New Server Cluster Wizard window, click the Next button.
6. In the New Server Cluster Wizard window, enter the IP address in the IP Address section, and click the Next button.
7. In the New Server Cluster Wizard window, enter the user name and password, and click the Next button.
8. In the New Server Cluster Wizard window, click the Next button. 9. In the New Server Cluster Wizard window, click the Next button.
10.In the New Server Cluster Wizard window, click the Finish button.
Configuring a Windows Server 2003 cluster
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