Since we are just getting started, I figure it’s appropriate to touch on the definition and composition of cloud computing. I have read and heard hundreds of definitions for cloud computing, and they all make good points. Nearly every single definition describes a computing solution in which resources, both hardware and software, scale up and down to meet the needs of the cloud consumer. That consumer may be an end-user accessing applications that run in the cloud, or it may be the application running in the cloud that depends on the lower layer services of the cloud. Most of the existing definitions also imply some autonomic capability in which not only does the cloud scale up and down, but it does so without administrator intervention based on policies declared by the consumer. Personally, I like many of these aspects, so I have tried to combine the elements that I think are most important: Cloud computing provides computing resources in a scalable, autonomic, governable fashion. These resources may be software, application infrastructure, or physical infrastructure, and the overall solution enables IT to be delivered as a service.
Attempting to define the anatomy of cloud computing seems to elicit as many opinions as defining cloud computing. For me, the three-layer approach sums it up quite nicely. While it’s true that some cloud solutions span multiple layers, the Google App Engine comes to mind, it provides at least a reference point for the discussion of cloud products.
- Application Services: This layer is comprised of what we have come to know as Software as a Service. This layer is very familiar to us (GMail, Facebook, MySpace, etc.), and it is equally familiar with enterprise consumers (WebSphere sMash on EC2, Salesforce, Sugar CRM, etc.).
- Platform Services: The platform services layer is made up of different services that support applications. This may include middleware, connectivity, data, and messaging services. Offerings, such as WebSphere Application Server Virtual Images, SimpleDB on AWS, and Memcache from Google are all good examples of platform services.
- Infrastructure Services: Infrastructure services provide physical resources as needed. These include hardware, networking, storage, and more. IBM’s Blue Cloud, Amazon’s EC2, and Google App Engine are examples of infrastructure service providers.
Looking at all three layers, it’s plain to see that starting with application services, each layer builds on the other. However, that does not mean that each layer cannot be used independently of the other. In fact, companies often construct on-ramp paths to cloud computing that start with services in only one of the layers (i.e. virtualization of hardware).
So, there's my shot at defining cloud computing! To be sure, my view of the cloud has evolved over time. The more opinions and thoughts I read, the more I challenge my own view. For that reason, I’d like to hear what you think. What is the definition and anatomy of your cloud?