The objectives of computer clusters are their high availability and performance, as well as the improvement of data throughput by means of load balancing. These objectives are realized by the three groups of High Availability Clusters (HAC), High Performance Clusters( HPC) and scalable clusters for load balancing.
The high availability cluster stands for high reliability. Such a cluster is all about redundancy. In high availability clusters, the critical components and storage systems or even the entire nodes are redundant. If a node fails, the redundant node takes over the function of the faulty component. Depending on the constellation, both nodes, the primary and the secondary, can be active in high-availability clusters and perform load balancing. However, only one can be active and the other passive and operated in standby.
High availability clusters are used wherever low downtime is a concern, such as in production, but also in mission-critical applications such as web servers, mail servers or databases.