This section discusses onsite network load balancing (NLB). Performing NLB using Azure will be discussed later in this chapter. So, the first thing we have to discuss is why you would choose to use NLB. NLB lets you configure two or more servers as a single virtual cluster. It’s designed for high availability and scalability of Internet server applications. This means that Windows Server 2022 NLB is designed to work with web servers, FTP servers, firewalls, proxy servers, and virtual private networks (VPNs).
You can use NLB for other mission- critical servers, but you can also use failover clusters on many of these servers. So, after reading this and the next chapter (“Hybrid Data and Servers”), hopefully you will be able to choose the appropriate high availability server setup for your network and applications.
NLB is a form of clustering where the nodes are highly available for a network- based service. This is typically a port listener configuration where a farm of, say, Microsoft Internet Information Services servers all listen on ports 80 and 443 for incoming web traffic from client endpoints. These nodes, while not fully clustered in a technical sense, are load balanced, where each node handles some of the distributed network traffic.
The NLB feature uses the TCP/IP networking protocol to distribute traffic. For web and other necessary servers, NLB can provide performance and consistency when two or more computers are combined into a single virtual cluster.
Hosts are servers that make up an NLB cluster. Each host runs its own individual copy of the server applications. The incoming client requests are distributed by NLB to each of the hosts in the cluster. You can configure the load so that it is handled by each host. Hosts can be added to the cluster to increase the load. If NLB has all traffic directed to a specific single host, then it is called a default host.
With the use of NLB, all the computers in a cluster can use the same set of IP addresses while each host maintains its own exclusive IP address. When a host fails for load- balanced applications, the computers still in operation will receive the workload automatically. When the down computer is ready to rejoin the cluster, it comes back online and will regain its share of the workload. This allows the rest of the computers in the cluster to handle less traffic.
NLB is beneficial in that stateless applications (e.g., web servers) and are available with little downtime, and it allows for scalability. Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate growth. Scalability, when used for NLB clusters, is the ability to add one or more systems to an existing cluster when the need arises. You can do the following with NLB to support scalability:
■ A single cluster can support up to 32 computers.
■ Handle multiple server load requests from across multiple hosts in a cluster.
■ For single TCP/IP services, balance-l oad requests across the NLB cluster.
■ As the workload grows, you can add hosts to the NLB cluster without failure.
■ When the workload declines, you can remove hosts from the cluster.
■ Allow higher performance and lower overhead by using a pipelined implementation.
Pipelining allows requests to be sent to the NLB cluster without waiting for a response.
■ Use NLB Manager or Windows PowerShell cmdlets to manage and configure NLB clusters and hosts from a single computer.
■ Determine port rules for each website. Port rules allow you to configure which ports are going to be enabled or disabled. Ports are doorways that applications can use to access resources. For example, DNS traffic uses port 53 for all DNS traffic. Here are some of the more common port numbers:
■ FTP uses ports 20/21.
■ Secure Shell uses port 22.
■ SMTP (mail) uses port 25.
■ DNS uses port 53.
■ HTTP uses port 80.
■ POPv3 uses port 110.
■ HTTPS uses port 443.
■ Determine load balancing behavior using port management rules for an IP port or group of ports.
■ Use an optional, single- host rule that will direct all client requests to a single host. NLB will route client requests to a specific host that is running particular applications.
■ Allow certain IP ports to block unwanted network access.
■ When operating in multicast mode, enable Internet Group Management Protocol (IGMP) support on the cluster host. This will control switch port flooding (when all incoming network packets are sent to all ports on the switch).
■ Use Windows PowerShell to start, stop, and control NLB actions remotely.
■ Check NLB events using Windows Event Log. All NLB actions and cluster changes are logged in the Event Log.
NLB Requirements
The following are NLB cluster hardware requirements:
■ All hosts must be on the same subnet.
■ For each host, there is no limitation to the number of network adapters.
■ All network adapters must be multicast or unicast within the cluster. Mixed environments, within a single cluster, are not supported.
■ If using unicast mode, the network adapter used to handle client- to- cluster traffic must support media access control (MAC) address changing.
NLB cluster software requirements are as follows:
■ The adapter on which NLB is enabled can only support TCP/IP.
■ Must have a static IP address on the servers in the cluster.
