When a server fails, traffic is diverted to another server in the cluster. 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.
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.
It is used to specify the host's unique IP address, which is used for non-cluster network traffic i. This must be a fixed IP address and not a DHCP address and as such should also be entered into the network properties dialog of the node. To configure dedicated IP addresses, click on the Add The Initial host state setting controls the initial state of the node when the system is started. The default is for the server to start as an active participant in the cluster.
Alternative options are Suspend and Stop. Clicking Next displays the Cluster IP addresses screen. These are the virtual IP addresses by which the cluster will be accessible on the network. These IP addresses are shared by all nodes in the cluster and a cluster may have multiple virtual IP addresses. Once the cluster IP addresses are specified, click on Next to proceed to the Cluster Parameters screen:. Any additional operations on the NLB cluster should not be initiated until all cluster nodes have completed the convergence process and are back to the converged state.
To check the state of all cluster nodes, use the Get-NlbClusterNode cmdlet. If a configuration change results in the cluster nodes remaining in perpetual convergence, refer to the event log to resolve the configuration inconsistency between the cluster nodes.
Performs the operation without prompting for confirmation. By default this operation will ask for confirmation from the user before proceeding.
Specifies the name of the host which is part of the cluster to run this cmdlet against. Yes No. Thank you! Any more feedback? The more you tell us the more we can help. Can you help us improve? Resolved my issue. Clear instructions. Easy to follow. No jargon. Pictures helped. Didn't match my screen. Incorrect instructions.
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