In this post I will argue that the so-called "Cloud" computer programs are inherently unreliable. I will assume that the reader knows what "Cloud computing" means: essentially a marketing buzzword referring to network-based services offered by a third-party. The term "unreliable" is however not that much of a buzzword, and therefore I will spend a few paragraphs describing it.
Reliability, definitions
In short, reliability is a measure of whether stuff works at a given point or over a given period of time. By "stuff" I mean systems, in particular computer systems, the entire thing, both hardware and software. By "works" (which is the opposite of "fails", by the way) I mean that it performs a particular task that was specified beforehand by the user in non-ambiguous terms. For example, I want some software to tell me the weather forecast for the next couple of days. If said software gives me a result, then we say it's reliable, and vice-versa, if it fails to give a result then it's unreliable. Ideally, the software should also give a good result, but we don't know whether the result is good or bad unless the program has been consistently giving bad forecasts over time. So good/bad results are often tricky1, and we don't want to complicate things too much.
Wikipedia2 also gives a brief definition, actually a set of definitions, of reliability:
Reliability is theoretically defined as the probability of failure, the frequency of failures, or in terms of availability, a probability derived from reliability and maintainability.
The probabilistic approach is interesting: if a thing has a high probability of failing, then it's unreliable. Availability is more used in practice, especially for server uptime: if a service works properly 99.9999% of the time in a year, then it is highly available, or in other words, pretty reliable. Remember that software is different from hardware, in that it doesn't degrade because of physics, but rather because of the sheer stupidity of developers3.
Now that we've established possible definitions of reliability, let's give some examples illustrating the unreliability of Cloud services.
Examples of Cloud unreliability
Scenario 1: The GitHub project. GitHub is one of my favourite Cloud providers, which is why I'm giving it as an example and keeping it in mind myself. So, you're the CEO of a company, working for an important software project. It's been decided that all development files will be hosted on a private GitHub repository. You're one day before deadline, the clients have their eyes on you, and you know you're gonna lose lots of dollars if this fails. By some weird occurrence, GitHub servers fail. Chaos ensues.
But well, the reader might argue, this could have happened as well on a privately hosted server. And I will answer aye, indeed, it could have. Only that if it happened on a private server, someone could be held accountable for the failure: the sysadmin, some hacker, well, some entity. In the case of GitHub, basically no one can be held accountable. Certainly not GitHub, it was stated in their ToS last time I looked.
Scenario 2: Google's supercalifragilistic mailing service. I use this one as well and I hate myself for it. The main concern here is not of availability, given that Google seem to be deep there in the energy sector, among others. The problem lies in security, more specifically in the fact that some 14-year old kid can easily break into my account if for example Google decide to use crappy certificates at some point in time. In fact, Computer Security 101 tells us pretty clear that the security risk doesn't come from known threats, but from vulnerabilities that haven't been discovered yet.
That can be easily generalized to the entire Cloud computing environment. Leaving aside NSA snooping issues that can easily break your business4 if you're doing stuff that's not approved by the US government, the subject of Cloud computing security is a bit of a nasty bugger here. There have been some successful attempts to drive away crackers from virtual machines running in the Cloud, but the problem isn't this, it's that the unknown is so big. I'd link to some literature on the subject, only I haven't seen any last time I looked. If that doesn't scare you, then you're just ignorant. If by any chance you know more than I do, please link that in an e-mail.
Plus, I have to mention the NSA snooping issues again. We're all ignorant about that, which is at least as scary.
Scenario 3: The Google Reader. I'm sorry I have to blurt it out on Google like that, but they're the company that have recently had the most cases of Cloud software going down suddenly. These cases show well that Cloud companies don't give a damn about their customers. They want to make money, which is ok for any business, that is, until making money starts becoming contrary to customers' interests.
So you're a Google enthusiast. You've noticed the takedown of Google Notebook, Google Translate API etc. Finally, after all these years, they also take down Google Reader. What now? Are you going to move to yet another web-based RSS reader that's going to close sooner or later? Good for you.
Cloud software is thus inherently unreliable due to being inherently closed and untrustable, unless you can get the code, compile it and run your own instance. Google could have removed sensitive parts of their Reader and open sourced it, but I suppose they really did just not give even the smallest damn.
Conclusion
The examples above are not strong, in the sense that they don't describe systems which should be necessarily dependable. Google Reader closed and the world moved on, people can live with having their [insert Cloud service here] accounts hacked and downtimes are ok as long as they don't cause permanent damage such as loss of data. Keeping all (and by all I mean all) your personal files exclusively in the Cloud is a big issue though, and I hope no sane individual does that, for their own sake.
Some political-economical pros and cons could also be discussed. For example, many people insist on comparing the Cloud (ex-"Grid") with the electrical grid. Surely, you're paying your electricity company for energy and your ISP for Internet, so why wouldn't you pay your Cloud provider for hard-disk space, an office suite, a book or an MMORPG? Besides implications related to personal rights and freedoms5, the ironical thing is that small companies and individuals are trying to stick it to the man and move away from the centralized energy distribution model by installing small windmills and/or solar panes. And that's pretty much the future, maybe not entirely, but at least partially. Well, commercial computing seems to be heading the opposite way, putting way too much power in the hands of corporations. Don't believe me, I'm nobody. Read Schneier's point of view.
Overly-centralized systems lack stability. Cloud services are unreliable. This seems to somehow fit nicely into the big picture. ▪
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Sometimes depending on the user. ↩
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For all you science purists out there, I am well aware that Wikipedia is not a particularly good source of information. However, the definition is pretty good. I've learned it myself in faculty, I know it's good. Don't believe me? Then go find it for yourself in an engineering book, just make sure you don't pester me about it, mkay? ↩
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What I'm saying is that, theoretically, if a piece of software works at version 1 and then it (partially or totally) stops working at version 2, then that makes that piece of software pretty unreliable. Unfortunately, developers often introduce bugs in their software for various reasons, but we can dumb that down to sheer stupidity.
Sure, we could look at it the other way and say that well, software is pretty damn complex, which it obviously is. But engineering stuff that you don't understand is indeed rather stupid, so the bridge-software analogy holds well in the field of software reliability. Tell that to the people who've died in the Challenger disaster, I'm sure they'll agree with you. Oh wait, they can't, they're dead. ↩
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And quite possibly you. ↩
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No, you don't own your Amazon e-books, your Steam games and your Spotify music. It sucks, doesn't it? ↩
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