If you’re a system administrator, you’ve already had it happen: you’ve just ordered lunch when your pager goes off. No lunch for you today. Or maybe you’re on the other side of the fence: the server is down, and your system administrator can’t be found. You miss your deadline because no one’s available to fix your critical system.
High-availability (HA) clusters can dramatically cut downtime, and since service failovers are fast and automatic, system administrators get to finish their lunch and users get to finish their work. “Admins” are happy, users are happy, even pointy-haired managers are happy, because minimizing work stoppages saves money.
Although high-availability means different things to different people, here it refers to highly-available clusters. An HA cluster is a set of servers that work together to provide a set of services. In an HA cluster, services don’t belong to any one server in the cluster, but to the cluster as a whole. If one server fails, its services are provided quickly and automatically by another server.
While HA systems can’t eliminate outages completely, they can make hiccups very, very short. And when they’re short enough, they can go unnoticed or will get blamed on something else — like a “glitch” in the Internet. When working as it should, an HA system is like an illusionist’s trick, where the hand is faster than the eye. Indeed, an HA cluster that’s properly designed, configured, installed, and managed should add a “9″ to…
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