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. 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.
Privacy policy. For example, you have found nodes in the cluster and want to check whether Load Balancing is working or not. Create different four shares on four nodes and try to access them from one machine. You must get each time different share when browsing using UNC patch.
NLB doesn't detect application failure. Automatically detects and recovers from a failed or offline computer. Automatically balances the network load when hosts are added or removed. Recovers and redistributes the workload within 10 seconds. The load is automatically redistributed to other nodes when a host goes offline. All the active connections to that host are lost. If you're internationally taking a node offline, then you can use the drainsstop command to service all the active connections before you take the node offline.
You can have a mix of applications running in the NLB cluster. This way you can designate the traffic for database to SQL server node only. NLB can load balance multiple requests from client on the same node or different node. This is done randomly. NLB automatically detects and removes the failure of NLB Node but it can't judge whether an application is running or stopped working. This should be done manually by running a script. Automatically load balances when new hosts are added or removed and this is done within 10 seconds.
NLB can be enabled on multiple network adapters. This allows you to configure different NLB Cluster. NLB can operate in two modes - Unicast or Multicast but both the modes can't be enabled at the same time.
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. A single computer running Windows can provide a limited level of server reliability and scalable performance. However, by combining the resources of two or more computers running one of the products in Windows Server into a single virtual cluster, NLB can deliver the reliability and performance that Web servers and other mission-critical servers need.
Each host runs a separate copy of the desired server applications such as applications for Web, FTP, and Telnet servers. NLB distributes incoming client requests across the hosts in the cluster. The load weight to be handled by each host can be configured as necessary. You can also add hosts dynamically to the cluster to handle increased load. In addition, NLB can 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 cluster 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 a computer fails or goes offline unexpectedly, active connections to the failed or offline server are lost.
However, if you bring a host down intentionally, you can use the drainstop command to service all active connections prior to bringing the computer offline. In any case, 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.
Hardware and software considerations for NLB clusters. In the case of virtual clusters, the servers do not need to be multihomed to have multiple virtual IP addresses. NLB can be bound to multiple network adapters, which allows you to configure multiple independent clusters on each host. Support for multiple network adapters is different from virtual clusters in that virtual clusters allow you to configure multiple clusters on a single network adapter.
Do not add any other protocols for example, IPX to this adapter.
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