One way of dividing server clusters into types is by their intended purpose.
High-availability clusters are used in order to guarantee maximal reliability. You should invest in a high-availability cluster if your services cannot afford to experience any downtime.
HPC (high performance computing) clusters are used for heavy workloads that require a significant amount of computing power. HPC clusters can quickly handle large volumes of data.
Load-balancing clusters distribute workloads equally between nodes. This type provides maximal stability, eliminating the possibility of peak loads affecting a single node.