Distributed Systems

Distributed systems have changed the face of the world. When your web browser connects to a web server somewhere else on the planet, it is par-ticipating in what seems to be a simple form of a client/server distributed system. When you contact a modern web service such as Google or face-book, you are not just interacting with a single machine, however; be-hind the scenes, these complex services are built from a large collection (i.e., thousands) of machines, each of which cooperate to provide the par-ticular service of the site. Thus, it should be clear what makes studying distributed systems interesting. Indeed, it is worthy of an entire class; here, we just introduce a few of the major topics. A number of new challenges arisewhen building a distributed system. The major one we focus on is failure; machines, disks, networks, and software all fail from time to time, as we do not (and likely, will never) know how to build “perfect ” components and systems. However, when we build a modern web service, we’d like it to appear to clients as if it never fails; how can we accomplish this task? THE CRUX: HOW TO BUILD SYSTEMS THAT WORK WHEN COMPONENTS FAIL How canwe build aworking systemout of parts that don’t work correctly all the time? The basic question should remind you of some of the topics we discussed in RAID storage arrays; however, the problems here tend to be more complex, as are the solutions. Interestingly, while failure is a central challenge in constructing dis-tributed systems, it also represents an opportunity. Yes, machines fail; but the mere fact that a machine fails does not imply the entire system must fail. By collecting together a set of machines, we can build a sys-tem that appears to rarely fail, despite the fact that its components fail regularly. This reality is the central beauty and value of distributed sys-tems, and why they underly virtually everymodern web service you use