A single point of failure is a component that would cause the whole system to fail if it fails. If a business has one server running an application, that server is a single point of failure. Should that server fail, the application will be unavailable.
High Availability
Highly available systems must be well-designed and thoroughly tested before they are used. All of the components are required to meet the desired availability level when planning one of these systems. In order to ensure that HA systems are able to meet their availability objectives, data backup, and failover capabilities play an important role. The technology used to store and access the data must also be carefully monitored by system designers.
How does high availability work?
Reliable crossover
Building redundancy into these systems is also important. Redundancy enables a backup component to take over for a failed one. When this happens, it's necessary to ensure reliable crossover or failover, which is the act of switching from component X to component Y without losing data or affecting performance.
Failure Detectability.
Failures must be visible and, ideally, systems have built-in automation to handle the failure on their own. There should also be built-in mechanisms for avoiding common cause failures, where two or more systems or components fail simultaneously, likely from the same cause.
Types of Availability
