Achieving high availability can be costly. Therefore, it is important to ensure that you align your application availability requirements with your business objectives. There are several options to achieve the level of availability that is right for your application. Hence, it is essential to start with a clearly defined set of availability objectives and then make the most prudent design choices to achieve those objectives at a reasonable cost. Typically, all systems and services do not need to achieve the highest levels of availability possible; at the same time ensure you do not introduce a single point of failure in your architecture through dependencies between your components. For example, a mobile taxi ordering service needs its ordering-related service to be highly available; however, a specific customer's travel history need not be addressed at the same level of availability.

The best way to approach high availability design is to assume that anything...