Configuring Windows Server Clusters

In Enterprise network, group of servers are often used to provide a common set of services. For

example, Different physical computers can be used to answer request directed at a common web site or

database server. These servers group are often referred as Clusters. In Windows Server 2008, we can

configure three types of server groups for load balancing, scalability and high availability. In this article

we will discuss about the load balancing and high-availability server clusters we can configure in

Windows Server 2008.

We can configure three types of server groups in windows server 2008.

Round-Robin Distribution Group

Network Load Balancing (NLB) cluster

Failover Cluster

First, a Round-Robin distribution group is a group or set of computers that uses DNS to provide basic

load balancing with minimal configuration requirements. It is very simple method for distributing a

workload among multiple servers. In round-robin, a DNS server is configured with more than one record

to resolve another servers name to an IP address. The purpose of DNS round robin is to load balance

client request among servers. Its main advantage is that it is very easy to configure. Round-Robin DNS is

enabled by default in most of the DNS servers, so you only need to create the appropriate records on

the DNS server. However the biggest drawback is that if one of the servers goes down, the DNS servers

does not respond to this event and will keep directing client request to this inactive server until

administrators removes the DNS record from the DNS servers. Another disadvantage is that every

record is given equal weightage, regardless of whether one target server is more powerful than another.

Because of these serious limitations this method is not recommended to use in a large production

network. And we will see next how network load balancing overcome these limitations.

NETWORK LOAD BALANCING

NLB or Network Load Balancing cluster is an installable feature of server 2008 which distributes client

request among servers in an NLB cluster by using virtual IP address and a shared name. From the client

perspective, NLB cluster appears to be a single server. In a common scenario, NLB is used to create a

Web farm a group of computers to support a web site or a set of web sites. Also it can be used to

create a terminal server farm, a VPN server farm, or an ISA server firewall cluster. But its not suitable

for the clusters where data changing occurs most, for example SQL database cluster, file server cluster.

For this type of group of servers Microsoft has a cluster solution knows as failover cluster which we will

see later in this article.

NLB provides some advantages over round-robin DNS method. First of all, NLB automatically detects

servers that have been disconnected from the NLB cluster and then redistributes client requests to the

remaining live hosts. This feature prevents clients from sending their request to failed server. Another

difference is NLB have the option to specify a load percentage that each host will handle.

CONFIGURING AN NLB CLUSTER In this section we will learn how to configure an NLB cluster. To demonstrate I have used following

servers and role in my lab:

Domain: abhi.local

Domain Controller: DC01.abhi.local with an IP address 192.168.1.1

Member Servers: Node1.abhi.local with an IP address 192.168.1.15

Node2.abhi.local with an IP address 192.1681.16

Creating an NLB cluster is very simple process. To begin, on both nodes Node1.abhi.local and

Node2.abhi.local configure the service or application (such as IIS) that it provide to clients. Please make

sure to create identical configurations because you want the client experience to be identical regardless

of which server users are connected to. For this lab purpose I have installed IIS and configured a default

web site on both the nodes.

The next step is to install Network Load Balancing feature on both the nodes since both node are going

to join NLB cluster. To do so, perform following steps on both the nodes:

Open Server Manager, and then click Add Features. In this wizard, select Network Load

Balancing, click next and follow the prompts to install.

Once this install on both the nodes, the next step is to use Network Load Balancing Manager to

configure the cluster. To configure, perform the following steps:

Launch Network Load Balancing Manager from Administrative Tools or you can also open by

typing Nlbmgr.exe from a command prompt. In the Network Load Balancing Manager console

tree, right click Network Load Balancing Clusters and then click New Cluster.

Connect to the host that is part of this new cluster. In this lab the node is Node1.abhi.local and

Node2.abhi.local. I will add Node1 first and configure the properties then I will show you how to

add another node in cluster.

As you seen from above figure I have entered the Node1 and clicks connect, then I have to select the interface

which we want to use with cluster. In this case it is Node IP address 192.168.1.15. The other interface is having

the IP address of different subnet than local area network because that one will used for cluster communication,

which we will see later during failover configuration.

On the Host Parameters page, select a value in priority. The host with lowest numerical priority

among the current members handles all the clusters network traffic not covered by a port rule.

For this lab I have given priority 1 to Node1.

On the Cluster IP Address page, click Add to enter the cluster IP address shared by every host in

the cluster. Please note that NLB doesnt support DHCP. NLB disables DHCP on each interface it

configures, so the IP address must be static. Also note that the IP Address which we entered

here is not the IP address of any servers/node, this IP address will represent the cluster IP

address. Here in this lab I have given an IP address 192.168.1.20. Click next

On the Cluster Parameters page, in the Cluster IP Configuration area, verify appropriate values

for IP address and subnet mask, and then type a fully qualified domain name for cluster.

As you seen from above figure I have verified the IP address details and entered the FQDN of cluster as

nlbcluster.abhi.local. This wizard generates a uniquely cluster MAC address which client used for serving

request to group of servers. Here its a very interesting thing, if you notice the IP generated MAC address, the

last four bit is hexadecimal value of the given IP address. Also please note that FQDN is not needed when using

NLB with Terminal Servers.

Also from above figure, we have three options for Cluster Operation mode. In Unicast mode, the MAC address

of the cluster is assigned to the network adapter of the computer, and the built-in MAC address of the network

adapter is not used. It is recommended that you accept the unicast default settings. Click Next to continue.

Now we will see the Node1 status from the NLB console, and it is in converged state, means Node1 is ready to

do the cluster services and accept the directing request from client.

So the Node1 is successfully added in cluster. Lets add our second node Node2.abhi.local to cluster. To add

more hosts to the cluster, right click the new cluster nlbcluster.abhi.local and then click Add Host To Cluster.

Configure the host parameters (including host priority and dedicated IP address) for the Node2 following the

same instructions that we used to configure Node1.abhi.local. Because we are adding hosts to an already

configured cluster, all the cluster-wide parameters remain the same. Once this done, verify the status of Node2

from NLB manager console, as shown below:

Ok, so our NLB cluster has been configured with two nodes Node1 and Node2, having Node1 as a high host

priority 1 and Node2 host priority as 2. Now we will discuss Port Rules of network load balancing cluster. To do

so right click newly configured cluster nlbluster.abhi.local and click Cluster properties. And go the Port Rules

tab to view the port rule settings:

Currently the port rules defined the settings to accept request on all ports for the added nodes in cluster. Since

in this lab, we have installed IIS on both the nodes to accept the directing web site request. So in this scenario,

for a Web Services we need to enable port 80 for HTTP traffic. So we have to configure this port rule so that the

new rule applies only to HTTP traffic. If you are using some other services for example terminal services you

have to enable port 3389 to 3389 rule that applies only to RDP traffic.

To enable port rule for web services, we need to do following:

On the Port Rule page, click Edit to modify the default port rules and type 80 to 80.

In the Protocols area, select TCP, as the specific TCP/IP protocol the port rule should cover.

In the Filtering mode, select Multiple Host if you want multiple hosts in the cluster to handle

network traffic for the port rule. Choose Single Host if you want a single host to handle the

network traffic for the port rule. In this lab both of the nodes are configured to query for

website request so I have selected Multiple Host.

In Affinity (which applies on