HP Integrity rx5670 Windows Integrity Cluster Installation and Configuration G - Page 10

Introduction Server Cluster vs. Network Load Balancing NOTE Server Cluster Use Server Cluster to provide high availability for mission-critical applications through fail-over. It uses a "shared-nothing" architecture, which means that a resource can be active on only one node in the cluster at any given time. Because of this, it is well suited to applications that maintain some sort of fixed state (for example, a database). In addition to database applications, ERP or CRM, OLTP, file and print, e-mail, and custom application services are typically clustered using Server Cluster. When you deploy Server Cluster, you first configure it between two and eight servers that will act as nodes in the cluster. Then you configure the cluster resources that are required by the application you're clustering. These resources may include network names, IP addresses, applications, services, and disk drives. Finally, you bring the cluster online so that it can begin processing client requests. Most clustered applications and their associated resources are assigned to one cluster node at a time. If Server Cluster detects the failure of the primary node for a clustered application, or if that node is taken offline for maintenance, the clustered application is started on a backup cluster node. Client requests are immediately redirected to the backup cluster node to minimize the impact of the failure. Though most clustered services run on only one node at a time, a cluster can run many services simultaneously to optimize hardware utilization. Some clustered applications may run on multiple Server Cluster nodes simultaneously, including Microsoft SQL Server. Network Load Balancing (NLB) Use NLB to provide high availability for applications that scale out horizontally, such as Web servers, proxy servers, and other services that need client requests distributed across nodes in a cluster. It uses a load balancing architecture, which means that a resource can be active on all nodes in the cluster at any given time. Because of this, it is well suited to applications that do not maintain a fixed state (for example, a Web server). NLB clusters don't use a quorum, and so they don't impose storage or network requirements on the cluster nodes. If a node in the cluster fails, NLB automatically redirects incoming requests to the remaining nodes. If you take a node in the cluster offline for maintenance, you can use NLB to allow existing client sessions to finish before taking the node offline. This eliminates any end-user impact during planned downtime. NLB is also capable of weighting requests, which allows you to mix high-powered servers with legacy servers and ensure all hardware is efficiently utilized. Most often, NLB is used to build redundancy and scalability for firewalls, proxy servers, or Web servers, as illustrated in Figure 1-1. Other applications commonly clustered with NLB include virtual VPN endpoints, streaming media servers, and terminal services. 10 Chapter 1