A server cluster consists of a set of connected servers that work together and can be seen as a single system. They are usually connected to a fast Local Area Network (LAN). The significant difference between a cluster and a group of servers is that the cluster acts as a single system trying to provide high availability, load balancing, and parallel processing.
If we deploy applications, or services, to individually managed servers and treat them as separate units, the utilization of resources is sub-optimum. We cannot know in advance which group of services should be deployed to a server and utilize resources to their maximum. Moreover, resource usage tends to fluctuate. While, in the morning, some service might require a lot of memory, during the afternoon that usage might be lower. Having predefined servers prevents us from having elasticity that would balance that usage in the best possible way. Even if such a high level of dynamism is not required, predefined servers tend...