The clustering is usually performed to provide high availability. A layer of cluster software runs on cluster nodes. Each node can monitor one or more nodes over the LAN.
The monitored machine can fail in some cases. The monitoring machine can take ownership of its storage. The monitoring machine can also restart applications that were running on the failed machine- The failed machine can remain down but the users will see a brief of the service.
The clustered system can be of the following forms:
• Asymmetric Clustering: In this form, one machine is in hot standby mode and other machine is running the application. The hot standby machine performs nothing. It only monitors the server. It becomes the active server if the server fails.
• Symmetric Clustering: In this mode, two or more machines run the applications. They also monitor each other at the same time. This mode is more efficient because it uses all available machines. It can be used only if multiple applications are available to be executed.