
154
Chapter 7
CHAPTER 7
Load-Balanced Clusters
More than 10 years ago, people discovered they could connect multiple cheap
machines to perform computing tasks that would normally require a mainframe or
supercomputer. NASA’s Beowulf cluster was an early example that is still in use
today (http://www.beowulf.org). A Wikipedia entry (http://en.wikipedia.org/wiki/
Computer_cluster) lays out the chief characteristics of a cluster succinctly:
A computer cluster is a group of loosely coupled computers that work together closely
so that in many respects they can be viewed as though they are a single computer.
Clusters are commonly, but not always, connected through fast local area networks.
Clusters are usually deployed to improve speed and/or reliability over that provided by
a single computer, while typically being much more cost-effective than single comput-
ers of comparable speed or reliability.
Clusters are a good solution when you’re looking to improve speed, reliability, and
scalability for a reasonable price. Amazon, Yahoo!, and Google have built their busi-
nesses on thousands of commodity servers in redundant cluster configurations. It’s
cheaper and easier to scale out (horizontally, by just adding more servers) than it is to
scale up (vertically, to more expensive machines). There are many Linux cluster solu-
tions, both open source and commercial. In this chapter we’ll discuss clusters based ...