High availability (HA) pertains to the ability of IT services to withstand all outages and continue providing processing capability according to some predefined service level.
One of the most important things you can do to facilitate solution recovery is to configure your system for High Availability (HA). Covered outages include both planned events, such as maintenance and backups, and unplanned events, such as software failures, hardware failures, power failures, and disasters. Clustered environments are highly available by nature because a clustered system is re-configured when a node or daemon failure occurs, so that workloads can be redistributed to the remaining nodes in the cluster.
A highly available solution is made up of a combination of hardware, software, and services that fully automate the recovery process and does not disrupt user activity. HA solutions must provide an immediate recovery point with a fast recovery time.
In a highly available solution, when the application server detects a problem, the transaction and the related data are moved to another server (either within the same data center or, in the case of a disaster, to a server in another geographic location) automatically. Moving the transaction and related data to another server is known as peer recovery.