Redundancy

N+1 redundancy

N+1 redundancy is a form of resilience that ensures system availability in the event of component failure. Components (N) have at least one independent backup component (+1). The level of resilience is referred to as active/passive or standby as backup components do not actively participate within the system during normal operation. The level of transparency (disruption to system availability) during failover is dependent on a specific solution, though degradation to system resilience will occur during failover. It is also possible to have N+1 redundancy with active-active components. In such cases, the backup component will remain active in the operation even if all other components are fully functional. However the system will be able to perform in the event that one component is faulted and recover from a single component failure. An active-active approach is considered superior in terms of performance and resiliency.

 

Failover cluster

A failover cluster is a group of independent computers that work together to increase the availability of applications and services. The clustered servers (called nodes) are connected by physical cables and by software. If one of the cluster nodes fails, another node begins to provide service (a process known as failover). Users experience a minimum of disruptions in service. The cluster can be configured on Azure