Failover Cluster
A failover cluster is a group of independent servers that are running Windows Server 2008 and working together to increase the availability of services and applications. When a failure occurs on one computer in a cluster, resources are redirected and the workload is redistributed to another computer in the cluster. You can use failover clusters to ensure that users have nearly constant access to important server-based resources.
Hardware and software considerations for failover clusters
Network Load Balancing
Network Load Balancing provides scalability and high availability to enterprise-wide TCP/IP services, such as Web, Terminal Services, proxy, Virtual Private Networking (VPN), and streaming media services. Network Load Balancing brings special value to enterprises deploying TCP/IP services, such as e-commerce applications, that link clients with transaction applications and back-end databases.
Choosing cluster technology in different usage:
Failover clusters are designed for applications that have long-running in-memory state, or that have large, frequently updated data states. These are called stateful applications, and they include database applications and messaging applications. Typical uses for failover clusters include file servers, print servers, database servers, and messaging servers.
Network Load Balancing is intended for applications that do not have long-running in-memory state. These are called stateless applications. A stateless application treats each client request as an independent operation, and therefore it can load-balance each request independently. Stateless applications often have read-only data or data that changes infrequently. Front-end Web servers, virtual private networks (VPNs), File Transfer Protocol (FTP) servers, and firewall and proxy servers typically use Network Load Balancing. Network Load Balancing clusters can also support other TCP- or UDP-based services and applications