A High Availability (HA) cluster is a set of servers (nodes) managed by clusterware to work together for
minimizing application downtime as much as possible. Clusterware enables servers to communicate
with each other, so that they appear to function as a collective unit. In an active-passive HA cluster,
there is one active server running the application, and one or more nodes standing by. If any problem
were to occur on the active node that prevents it from running the application, the clusterware is able
to detect this problem and start the protected applications on one of the standby nodes.
