The High availability clusters are computer clusters which are implemented mainly for the purpose of improving the availability of the services. The high availability clustering detect hardware/software faults, and instantly restart the application on another system without requiring administrative intercession, this process is commonly known as a Failover process. It has functionality that provides failover from one node to another if the current node becomes unavailable, a failover cluster appears on the network as a normal application, but it has additional functionality that increases its availability in case one server fail.

The clustering software may configure the node before starting the application on it. To run the system smoothly it require appropriate filesystems to be imported and mounted and  to set-up cluster rules that enable a common set of configurations also network hardware may have to be configured, and some supporting applications may need to be running as well.Diagram: HA Cluster network (2 node)

The purpose of HA clusters to utilize all available techniques to make the individual systems/shared infrastructure as reliable as possible. The high availability clustering should include the following;

* Build redundancy into a cluster.

* Redundant network connections so that a switchover or network interface failures do not result in network outages.

* Disk mirroring to avoid system crashes in case of failure of internal disks.

* SAN data connections.

* Redundant electrical power inputs.

The high availability clusters generally use a critical clustering in private network connection and monitor the status of each node in the cluster. Such clustering are often required for critical databases, business applications, file sharing on a network and customer services such as e-commerce websites.