High Availability Terminology

I'll start with the terminology used to describe high availability. I'm not going to split hairs at this point—I'll do that later, when I explore each concept in depth. The important thing here is that I introduce a vocabulary that allows us to talk about multiple computers working together to accomplish a task.

When a program runs, it is called a process. A process running on a Linux system is called a daemon. A daemon and the effects it produces is called a service. A service is called a resource when it is combined with its operating environment (configuration files, data, network mechanism used to access it, and so forth). A failover occurs when a resource moves from one computer to another. A proper failover or high-availability configuration has no single point of failure.^[1]

^[1]I'm departing from the Red Hat cluster terminology here, but I am using these terms as they are defined by Linux-ha advocates (see http://www.linux-ha.org).