For creating fault-tolerant and highly available servers, which solution is the BEST option?

Clustering is the best option for creating fault-tolerant and highly available servers because it involves linking multiple servers together in such a way that they work as a single system. In a clustered environment, if one server fails, the workload and services are immediately transferred to another server in the cluster, thereby minimizing downtime and maintaining availability. This redundancy is a core characteristic of high availability systems, allowing continuous access to resources without interruption.

Additionally, clusters can be set up to allow for load balancing, scaling, and redundancy, making them particularly effective in environments where uptime is critical, such as in enterprise applications or web services. The clusters can operate through various configurations (like active/active or active/passive setups) to enhance performance and reliability.

While load balancing and virtualization can contribute to high availability in different ways, clustering specifically addresses the need for fault tolerance by providing an immediate backup within the server architecture itself. Round robin is a technique often related to load distribution but doesn't inherently contribute to server availability or fault tolerance in the same direct manner that clustering does.