Always-on architectures

For many years, architects have always had two primary concerns: the availability of a given system and the recoverability of the system (often referred to as disaster recovery). These two concepts exist to address inherent qualities of a system deployed on a limited, on-premise infrastructure. In this on-premise infrastructure, there are a finite number of physical or virtual resources performing very specific functions or supporting a specific application. These applications are built in such a way that it negates the ability to run in a distributed manner across multiple machines. This paradigm means that the overall system has many single points of failure, whether it be a single network interface, a virtual machine or physical server, a virtual disk or volume, and so on.

Given these inherent fault points, architects developed two principle assessments to gauge the efficacy of a system. The systems' ability to remain running and perform its function is known as...