Now you’ve learned the finer art of setting up a Windows Server 2003 Cluster.
Next, you learn how to configure NLB, which is a completely different animal in its approach to high availability networking. As you previously learned, NLB is also called clustering, so don’t confuse it with the use of the name. “Clustering” is a generic term and you’ll find that it’s often used interchangeably. I’ll explain it as NLB clusters when applicable. Let’s prepare for NLB-based clusters and more Highly Available solutions with Windows Server 2003.
Where to Begin
Load balancing is balancing the amount of work a server must do between two or more computers. When applied to network available resources, we use the term “network load balancing.” Before we jump into working with NLB in Windows Server 2003, let’s step back and look at what Microsoft has done with NLB in the next generation of Windows Servers—this is quite an improvement over Windows 2000. Table 3-5 has a quick rundown of some points about moving to Windows Server 2003 NLB.
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Bidirectional Affinity Using Bidirectional Affinity enables you to cluster Internet Security and Acceleration (ISA) servers together for use as proxy and firewall load balancing. You typically use NLB with an ISA server for web publishing and server publishing. Although web publishing doesn’t require Bidirectional Affinity, server publishing does, so this is a great improvement for those running an ISA server in a NLB cluster. Bidirectional Affinity solves the server-publishing problem by creating multiple virtual instances of NLB on the host, which then work together to ensure the responses from each published server are routed through the appropriate ISA servers in the NLB cluster.
Internet Group Management Protocol (IGMP) Support When NLB is configured in multicast mode, you can use Internet Group Management Protocol (IGMP) support to limit the switch flooding caused by the NLB algorithm, which requires all hosts in the NLB cluster be able to see every incoming packet addressed to the cluster IP address. IGMP support can greatly conserve network resources by preventing switch flooding from occurring, except on those switch ports that have an NLB host connected to them.
Table 3-5. Server 2003 NLB Features
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A quick rehash of some of the general discussion related to Network Load balancing from Chapter 2 is appropriate, as you may have missed it if you skipped Windows 2000 network load balancing.
Typically, you use NLB for web-based traffic coming into your organization, splitting this load between more than one machine to improve response times and reliability.
NLB is almost always configured with a failover plan, so you can also have disaster recovery functionality incorporated into your load balancing solution. As you see in Figure 3-11, if you experience the failure of one server in the NLB cluster, you can still service user requests on the remaining three NLB cluster members. This transition occurs behind the scenes, completely unseen by the user.
Unlike with clustering, NLB isn’t appropriate for solutions that require a shared storage device, such as an SQLserver implementation on the back-end of an e-commerce web site. NLB would, however, be an appropriate solution to enhance the performance and availability of those front-end IIS servers serving up our web site to users. The determining factor why one solution is better than another is directly tied to the type of application being run. Clusters typically share a storage device, whereas NLB clusters don’t. Also, NLB is much more robust when it comes to reacting quickly to sharp changes
Network Load Balancing Manager Network Load Balancing Manager is a new utility in Windows Server 2003, which provides you with a single configuration point for the configuration and management of your network load balancing clusters. You can use the NLB Manager to perform the following tasks, plus several others such as:
Create new NLB clusters
Add and remove hosts to and from NLB clusters Manage existing clusters by connecting to them Configure NLB to load balance multiple web sites Configure NLB to load balance multiple applications Troubleshoot and diagnose improperly configured clusters Multi-NIC (Network Interface Card) Support Windows Server 2003 NLB can now be bound to more than one
NIC in a single host. This enables you to host more than one NLB cluster per server now, while still segregating them on to entirely separate networks.
Virtual Clusters The Virtual Clusters feature works similarly to Virtual Servers under IIS and enables you to perform tasks that, traditionally, you couldn’t perform when using NLB, such as:
Configure different port rules for different cluster IP addresses, where each cluster IP address corresponds to a web site or application being hosted on the NLB cluster
Filter out traffic sent to a specific web site or application on a specific host in the cluster
Table 3-5. Server 2003 NLB Features(continued)
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in network loading. New members can be easily “dropped” into an existing NLB cluster with little preparation ahead of time—the same isn’t true of clustering, as you know now. Also, NLB members can quickly react to the loss of a member server via the process of convergence, reassigning the load based on what servers remain after the casualty occurs. This makes NLB perfect for use with IIS applications, where fluctuations in load can occur sporadically, such as during the busy shopping period around the holidays.
Another area where NLB shines over standard clustering is managing session state and client affinity across members of the NLB cluster. These will be discussed in the upcoming section, “Multiple Host.” Another management tool you can leverage in NLB is port filtering.
Figure 3-11. Example of a network load balanced solution using Windows Server 2003
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NLB clusters make use of heartbeat traffic, just the same as Cluster Service clusters do. As you can see in Figure 3-12, a typical NLB cluster has one network segment for the front-end (public) traffic and another, separate segment for the back-end (heartbeat) traffic. The heartbeat traffic is what makes convergence work.
The last thing you should know about NLB clusters is they almost always have a lower cost to set up and maintain, and they also have much less stringent hardware
Figure 3-12. Example of a network load balanced solution using Windows Server 2003