Cluster is usually useful to reduce the load on a particular server.
Basically, clustering can be defined as the use of more than one computer/ server that can work together. In this type of architecture, multiple servers are liked to one another and has the capability of handling workloads. It helps to offer continued working and offer 100% uptime. All the machines in a cluster are involved in the operations at any given point of time. The cluster of servers offer fault tolerance. It is also termed as Load Balancing.
There are two types of clustering architectures offered by Web Hosting services providers.
A) Failover Cluster Server:
Multiple servers are involved in Failover Cluster. Failover clustering is different from Load Balancing servers. The term itself gives a little hint of what it is. Servers are placed in a cluster to offer high availability, though there is an hardware or software failure. If a hardware or software fails, a counter action is taken by the cluster itself and the resources are fetched from other servers to continue with the operations. There is a constant monitoring always active in the cluster to monitor the resources. A practical failover of software as well as hardware including the current status of applications can be achieved by fault tolerant fail over cluster.
Below is a pictoral description of Failover Cluster Server.
The basic intention of a load balancing architecture is to distribute the load among the servers in the cluster. A cluster can have more than one servers. You can keep adding servers to the cluster. These servers are set up in such a way that the traffic is distributed 
among all the servers. Its due to such an architecture that the network load gets re-distributed and is not focused on a single server. This helps in offering better reliability and gaining much improved performance.
There are common set of hardware that is required which is two server nodes in the cluster. Both the servers are connected to the network, both having their individual operating systems. Among the nodes, only one node is kept active at a given point of time. This is also termed as the “Active/Passive” solution. The resources of the cluster is utilized by the active server or the node and the data is written onto Shared Disks. Just incase if a node fails, the other node takes its place. To check if all the nodes are working properly, a signal known as ‘Heartbeat’ is sent across the network of the servers. If the active server fails to respond, the passive server gets triggered and starts functioning as an active server. The resources of the cluster are diverted to the passive server which is operating as the main active server.
Below are the Steps to Install a SQL Server in a cluster
It is important that the cluster is operational before you Install a SQL Server into the cluster.
a) You require Windows Server edition with a support to MSCS on every server.
b) One must get assured about every server in the cluster to be connected to the private network.
c) You must set up a different network and mind that you do not connect them to this network, it must only be used for sending the heartbeat signals.
d) You need to create a user account for the service accounts for the cluster to operate under this account in the domain. You also need to add every administrators group of every server.
e) Now you can connect the shared hard disks to the server then shut the servers off and switch on the node number one of the cluster.
f) Now you can install Microsoft Cluster and then configure it through the control panel.
g) Now, you must provide a name to the cluster and assign an IP address with the resources of the Shared Disk.
h) After all the above mentioned steps are followed, now you must turn ON the second node in the cluster and move to the Fist node, only when the second comes online.
This concludes the set-up of the cluster. You can refer the below guidelines to Install SQL server in the cluster.
a) You need to insert the CD SQL Server Enterprize edition, you may or may not have to do the installation manually.
b) Now you can choose the Virtual Server on the on the computer name screen and enter the name that you wish to have the Clustered referred as.
c) You need to now create a service account to run SQL web server that you provide administration rights on each node on the cluster.
d) You can allocate an IP address, Shared Resources and a service account to the SQL Server at the time of installation.