First, allow me to make a confession. In my own storied attempt to define cloud computing, I certainly sounded definitive in my definition. For example, I stated:
Cloud computing describes a systems architecture. Period. This particular architecture assumes nothing about the physical location, internal composition or ownership of its component parts. It represents the entire computing stack from software to hardware, though system boundaries (e.g. where does one system stop and another begin) may be difficult to define. Components are simply integrated or consumed as need requires and economics allow.For what its worth, I have found myself shifting a little; not so much on the definition, but on what exactly it defines. Given the largely consensus opinion that Cloud Computing refers to a service model, I am willing to concede that the description above really describes a "Cloud Oriented Architecture" for a complex integrated environment. The true definition of cloud computing is still evolving in my mind.
Now, back to the posts at hand. What I believe I am seeing these days is a split between two camps; the "cloud computing is only about services" camp, and the "cloud computing is getting what ever you need from the Internet" camp.
An example of the former comes from Randy Bias at NeoTactics:
"There seems to be a group myopia around so-called ‘cloud computing’ and it’s definitions. What we’re really talking about are ‘cloud services’ of which, ‘computing’, is only a subset. It gets worse when you have people talking about Software as a Service (SaaS) as a ‘cloud’ service. Things continue to become murkier when the SaaS crowd, bloggers, and reporters start making up new definitions for cloud services using SaaS-like terms such as Platform as a Service (PaaS) and Infrastructure as a Service (IaaS)."Scott Wilson of The CIO Weblog adds the following:
"When I think of a service as cloud computing, it is characterized by being an offering of nearly unlimited capacity (although it may be billed differently at different utilizations) which has some sort of generic utility but beyond certain minimal architectural requirements there should be no inherent specificity in what it may or should do. It may be a service of a certain type of utility, perhaps storage, raw processing capability, or data storage, but in the same way that a datacenter does not restrict what servers you may host with them, it should not restrict what sort of data you store, process, or serve."Sort of a "cloud services have a cloudy definition" kind of definition.
[Some definition links removed]
One of the best examples of the latter comes from ProductionScale's Joseph Kent Langley:
"Cloud Computing (Figure 1.0) is a commercial extension of computing resources like computation cycles and storage offered as a metered service similar to a physical public utility like electricity, water, natural gas, or telephone network. It enables a computing system to acquire or release computing resources on demand in a manner such that the loss of any one component of the system will not cause total system failure. Cloud computing also allows the deployment of software applications into an environment running the necessary technology stack for the purposes of development, staging, or production of a software application. It does all this in a way that minimizes the necessary interaction with the underlying layers of the technology stack. In this way cloud computing obfuscates much of the complexity that underlies Software as a Service (SaaS) or batch computing software applications. To explain better though, let's simplify that and break it down this definition to it's constituent parts."Langley's definition is more closely aligned with utility computing, but may be best summarized as a "if you can run it on the Internet, its a cloud".
Of course, there is also James Governor's famous list of requirements.
All of which leads to a gap in terminology that gets filled by whatever reaches the vacuum at the moment: what do you call a "cloud-like" infrastructure in a private data center? As I noted to the Google Groups Cloud Computing alias:
"[H]ere (is) how I arrived at that conclusion:I'm still hunting for the answer to that one.
- If "grid computing" is about running job-based tasks in a MPP model (e.g. HPC) (as it seems to be defined for many), and
- If "utility computing" is a business model for providing computing on an as-needed, bill-for-what-you-use basis, and
- If "cloud computing" is a market model describing services provided over the Internet (which it is for most of the Web 2.0 world), and
- If "virtualization" describes providing software layers in the execution stack to decouple software from the hard resources it depends on (and it is important to note for the purposes of this argument that "resource-pooled" does NOT require virtualization in this sense; it is quite possible to run your software on bare metal server pools, as we did at Cassatt)
Do we redefine "grid" to cover the expanded role of resource-pooled computing (as 3TERA seems wont to do)? Do we leverage "utility computing" as an adjective for platforms that can deliver that business model for those that own infrastructure (as Cassatt and IBM tend to do)? Does the term "virtualization" represent a broader view than how VMWare, Microsoft and Citrix are defining it? Is there another term (such as "resource-pooled computing"--ugh) that would better serve the discussion?"
- Then, what do we call the systems/infrastructure model where resources are pooled together, and used for a variety of workloads, including both job-based and "always running" tasks (such as web applications, management and monitoring applications, security applications, etc.)?
However, in terms of my definition of cloud computing, I have to say I lean towards the "anything you can run on the Internet" camp, as it--to me--best represents what an actual drawing of a cloud means in a system diagram. Just "go to the cloud" and get what you need, whether its a complete CRM system or a simple purchasing service. This eliminates a million potential grey areas at the boundaries of the "only about services" definition. Is PayPal a cloud service? Why or why not?
I'd love to hear from those of you that are beginning to see some consensus in online communities about what a constitutes a cloud or cloud service and what doesn't. In the meantime, I am settling down for another long summer of fog (this is the Bay Area, after all), though I'll have plenty of company, I'm sure.