You now know the finer art of setting up a Windows 2000 cluster. Next, we’ll discuss how to configure network load balancing (NLB), which is a different animal in its approach to high-availability networking. NLB is also called clustering, so don’t get confused with the use of the name.Clusteringis a generic term, and you’ll find it’s used interchangeably over and over again. In case you aren’t used to the IT jargon, I’ll explain it as NLB or network load-balancing clusters when applicable, so you won’t get confused. Let’s begin to prepare for NLB-based clusters and more Highly Available solutions with Windows 2000 Advanced Server. An example of a NLB solution using Windows 2000 can be seen in Figure 2-13.
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Where to Begin
Load balancingis balancing the amount of work (hence, “balancing the load”) that a server must do between two or more computers (up to 32 nodes). You can think of NLB or load balancing as being one of the main reasons for server-based clustering.
Load balancing is mainly used for the web, and all the traffic that comes and goes from what would have been one overwhelmed server. Now, you can have multiple servers in a group that will handle all that traffic and take the load off one single server serving requests.
Figure 2-13. Example of a network load-balanced solution using Windows 2000 Advanced Server
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NLB is usually connected to a failover plan, so you can also have disaster-recovery functionality incorporated into your balanced load. As you see in the previous diagram, you have a server failure, but the server is technically still up for client requests because you have two other servers available.
NLB is just as useful as generic two-node clustering, but it offers some specific features made for specific services. In other words, you might want to put a SQL Server 2000 installation on a dual-node cluster with a shared storage system, but you might want to put four NLB servers in a high-availability cluster running Internet Information Services (IIS) for a web site located across all four servers. You see, a difference in design exists, where one warrants more use than the other. With NLB, you have no single point of failure. If a node fails, then the rest of the available nodes reconverge and take up the load of the failed server. Instead of being locked down to two or four nodes, you can scale out to about 32 nodes with a NLB cluster. This is perfect for web sites that get more hits during holiday months, where you might want to add more nodes to distribute the load and make the single site you’re hosting appear able to take on the request, when it’s really a group of servers handling the load in an NLB cluster. The configuration is much easier as you see soon. Setting up an NLB cluster takes half the effort it took to set up a two-node failover cluster. NLB clusters are much more scalable than other types of clusters. You can add up to 32 nodes, add nodes at basically any time and with add-on software (discussed when you learn Application Center 2000), and you can monitor the health of all services and applications loaded across the NLB cluster. You can also filter via TCP/IP port for TCP- and UDP-based applications like HTTP, FTP, and others.
Another solution NLB offers over the Generic Cluster Services is the opportunity to manage session states across nodes and manage affinity. We’ll discuss this further in its own section. Heartbeats are still used with NLB and machine failure is detected in this fashion, as it was with Cluster Services. You still need to configure a public and a private network segment for your cluster.
Probably the most important things about designing a NLB cluster are lower cost and less-special hardware requirements than in the traditional cluster created with the Cluster Services, which has a demand for a shared bus. This is why most use the service over the other one. If you’re clustering SQL or Exchange Server 2000, though, you’ll need a shared storage drive, and then you’ll warrant using the Cluster Services. People ask me questions about cluster and NLB interoperability, and we can dispel this here: You either use NLB or MSCS. There’s no reason to run them both at the same time.
The Design Phase
We’ve reached the most important step of the NLB rollout. This section of the chapter mirrors the last one as closely in procedure, so you get the subtle (and not so subtle) distinctions between the two services—NLB and MSCS. When planning your NLB
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cluster, you should consider the following ideas. Remember, planning and preimplementation design goes a long way before the actual roll out.