NLB distributes incoming client requests across the hosts in the cluster. You can configure the load that is to be handled by each host. You can also add hosts dynamically to the cluster to handle increased load. NLB can also direct all traffic to a designated single host, which is called the default host. NLB allows all of the computers in the cluster to be addressed by the same set of IP addresses, and it maintains a set of unique, dedicated IP addresses for each host. For load-balanced applications, when a host fails or goes offline, the load is automatically redistributed among the computers that are still operating.
When it is ready, the offline computer can transparently rejoin the cluster and regain its share of the workload, which allows the other computers in the cluster to handle less traffic. NLB is useful for ensuring that stateless applications, such as web servers running Internet Information Services IIS , are available with minimal downtime, and that they are scalable by adding additional servers as the load increases.
The following sections describe how NLB supports high availability, scalability, and manageability of the clustered servers that run these applications. A high availability system reliably provides an acceptable level of service with minimal downtime. To provide high availability, NLB includes built-in features that can automatically:.
Scalability is the measure of how well a computer, service, or application can grow to meet increasing performance demands. For NLB clusters, scalability is the ability to incrementally add one or more systems to an existing cluster when the overall load of the cluster exceeds its capabilities.
To support scalability, you can do the following with NLB:. Balance multiple server load requests from the same client or from several clients across multiple hosts in the cluster. Enable high performance and low overhead through a fully pipelined implementation.
Pipelining allows requests to be sent to the NLB cluster without waiting for a response to a previous request. Specify the load balancing behavior for a single IP port or group of ports by using port management rules.
Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. NLB works by balancing traffic between the nodes in a Web farm or cluster. Servers emit a heartbeat message to other hosts in the cluster and listen for the heartbeat of other hosts. If a host fails, the remaining hosts adjust and redistribute the workload.
NLB does not monitor the health of your application. Instead, it allows the application developer to determine how healthy a load-balanced application is. Since each application has its own notion of load and health, measuring and monitoring these quantities is best achieved by the application itself. By using collected measurements from your application and the NLB public WMI provider, it is a relatively simple task to add load and health monitoring to your load-balanced application.
It is recommended that the servers have two networks. Scalability is the measure of how well a computer, service, or application can grow to meet increasing performance demands. For NLB clusters, scalability is the ability to incrementally add one or more systems to an existing cluster when the overall load of the cluster exceeds its capabilities. To support scalability, you can do the following with NLB:.
Balance multiple server load requests from the same client or from several clients across multiple hosts in the cluster. Enable high performance and low overhead through a fully pipelined implementation.
Pipelining allows requests to be sent to the NLB cluster without waiting for a response to a previous request. Specify the load balancing behavior for a single IP port or group of ports by using port management rules. Define different port rules for each website. If you use the same set of load-balanced servers for multiple applications or websites, port rules are based on the destination virtual IP address using virtual clusters.
Direct all client requests to a single host by using optional, single-host rules. NLB routes client requests to a particular host that is running specific applications. Enable Internet Group Management Protocol IGMP support on the cluster hosts to control switch port flooding where incoming network packets are sent to all ports on the switch when operating in multicast mode.
NLB logs all actions and cluster changes in the event log. NLB is installed as a standard Windows Server networking driver component.
The following figure shows the relationship between NLB and other software components in a typical configuration. Provides Network Load Balancing Tools to configure and manage multiple clusters and all of the hosts from a single remote or local computer. Enables clients to access the cluster by using a single, logical Internet name and virtual IP address, which is known as the cluster IP address it retains individual names for each computer.
NLB allows multiple virtual IP addresses for multihomed servers. Enables NLB to be bound to multiple network adapters, which enables you to configure multiple independent clusters on each host.
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