When the failed node is brought back online it is then re-assigned a share of the load. From a user perspective the load balanced cluster appears to all intents and purposes as a single server represented by one or more virtual IP addresses. The failure of a node in a cluster is detected by the absence of heartbeats from that node. If a node fails to transmit a heartbeat packet for a designated period of time, that node is assumed to have failed and the remaining nodes takeover the work load of the failed server.
Nodes in a Network Load Balanced cluster typically do not share data, instead each storing a local copy of data. Under such a scenario the cluster is referred to as a farm. This approach is ideal for load balancing of web servers where the same static web site data is stored on each node.
In an alternative configuring, referred to as a pack the nodes in the cluster all access shared data. In this scenario the data is partitioned such that each node in the cluster is responsible for accessing different parts of the shared data.
This is commonly used with database servers, with each node having access to different parts of the database data with no overlap a concept also known as shared nothing. Windows Server R2 Network Load Balancing clustering can be configured using either one or two network adapters in each node, although for maximum performance two adapters are recommended. In such a configuration one adapter is used for communication between cluster nodes the cluster adaptor and the other for communication with the outside network the dedicated adapter.
Network Load Balancing may be configured on a port by port basis or range of ports. For each port three options are available to control the forwarding of the traffic:. As such, the server application will typically maintain some form of session state during the client server transaction. Whilst this is not a problem in the case of a Single Host configuration described above, clearly problems may arise if a client is diverted to a different cluster node partway through a session since the new server will not have access to the session state.
Windows Server R2 Network Load Balancing addresses this issue by providing a number of client affinity configuration options. Client affinity involves the tracking of both destination port and source IP address information to optionally ensure that all traffic to a specific port from a client is directed to the same server in the cluster.
The available Client affinity settings are as follows:. The servers in an NLB cluster are called hosts , and each host runs a separate copy of the server applications. 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.
Just got it to work. Eric thanks for the link, it got me going in the right direction. But I was finally able to get the load balancing implemented by using the following technet article since it applies to Windows Server R2. Server has its own load balancing technologies, but I use 2X loadbalancers here and they work great. They do not do simple round-robin loadbalancing, they can check the utilization of each server and send load according to the least utilized. I'm not that familiar with , but we use the built-in network load balancing along with a session directory server for our terminal servers and it works pretty well.
In the list of available features, select Network Load Balancing and click on Next followed by Install. Network Load Balancing may also be installed from a command prompt with elevated privileges right click on the command prompt in the Start menu and select Run as administrator by running the servermanagercmd -install nlb command.
For example:. Once loaded, the manager will appear as shown in the following figure:. Note that the account must be a member of the administrators group. If default credentials are configured, the user will be prompted for account and password information each time a connection to a cluster node is established. To begin the cluster creation process, right click on the Network Load Balancing Clusters entry in the left panel of the manager window and select the New Cluster menu option.
This will display the New Cluster connection dialog. In this dialog, enter either the name or IP address of the first server to be included in the load balanced cluster and press the Connect button to establish a connection to that server.
If the connection is successful the first server will be listed as shown below:. Clicking Next will display a warning that DHCP will be turned off for the network adapter of the specified host and that any necessary gateway information will need to be configured manually using the server's network connection properties dialog accessible from the Control Panel. Subsequently, the Host Parameters screen will appear as shown below:. The Priority unique host ID is a number between 1 and 32 and serves two purposes.
Firstly, the number provides a unique ID within the cluster to distinguish the server from other nodes. Secondly, it specifies the priority order of the cluster.
The cluster node with the lowest priority is assigned to handle all traffic that is not covered by a port rule. All servers joining a cluster must have a unique ID. A new server attempting to join a cluster with a conflicting ID will be denied membership.
The Dedicated IP addresses fields are used when a single network adapter is used for both communication between cluster nodes and external network traffic.
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