Which type of system allows for software patching without incurring downtime?

The type of system that allows for software patching without incurring downtime is a clustered system. In a cluster, multiple servers (nodes) work together as a single system, providing redundancy and load balancing. When one node requires a patch or update, it can be taken out of the load balancer's pool, and the workload can be redistributed among the other nodes in the cluster. This approach ensures that users continue to receive services without interruption, as the live nodes maintain operational continuity while the patched node is updated.

Clustered environments are specifically designed for high availability and reliability, making them ideal for scenarios where uptime is critical. By managing updates in such a way that at least one node is always operational, clusters minimize the impacts of maintenance and software patching, thus achieving zero downtime for end users.

In contrast, single-node systems lack redundancy, meaning that any maintenance or software updates can lead to complete service interruption. Virtual machines can support uptime through live migration, but they typically require advanced configurations and may still experience brief interruptions during patching. Microservices architectures enhance deployment flexibility but do not inherently eliminate downtime related to software patching unless implemented with additional strategies for high availability.