Cloud Computing: Strata

	Ph. D. Julio Fernandez Vilas
	¿Any comments? jfvilas@gmail.com

There is no standard definition of what "Cloud Computing" is, and two reasons are responsible for this lack:

1. There are different implementation models (infrastructure, application, software ...), so there is no precise definition.
2. b) There are very multifarious offerings providers, so that a strict definition would not include all offerings.

But if I had to define what Cloud Computing is, I would choose the definition included in Wikipedia (read the interesting Wikipedia entry here):
"Cloud computing Relies on sharing of resources and coherence to Achieve Economies of scale, similar to a utility (like the electricity grid) over a network. At the foundation of cloud computing is the concept of Broader Converged Infrastructure and shared services. " The figure below is a good graphic illustration of generic architecture of cloud computing, where we can observe 3 clearly defined levels:

Here we can see the main "three flavors" of cloud computing offerings, infrastructure as a service (IaaS) platform as a service (PaaS) and application (it stands for "application software") as a service (SaaS). In the market and specialized press we can find other types of cloud offerings, focused on specific areas of technology, Security as a Service (SECaaS), Storage as a Service (STaaS), etc., but ultimately, any offering cloud will be framed in any of the three categories we've mentioned:

1. Infrastructure (IaaS) refers to the possibility of consuming infrastructure services in the cloud, such as computing power, storage, connectivity, etc. At this level, management done by the customer (subscriber) is performed at virtual machine level or storage unit (LUN) level, for example, while the provider of infrastructure services (provider) is responsible for "only" managing the hardware (plus all related concepts to the cloud, such as scalability, high availability, etc.).
2. Platform (PaaS). When a client wants to get rid of costs and tasks associated with the management of the infrastructure (machine maintenance, procurement of space, bandwidth allocation, etc.), he has the option of using services in a “platformed” mode, where the level of management that must been made by the subscriber is much lower than the one a provider to does. In this model, the client focuses on the development of applications, in fact the real solutions to their business problems. As an example, in Azure platform, it is possible to develop a .net web application and deploy a packetized version to a cloud server without installing anything. Here is Microsoft itself who is responsible for configuring and managing machines and application servers, clients only have to worry about generating deployable software packages on the platform. At this level of the cloud computing stack is where you would frame the old ASP's (application service providers).
3. Software / Application (SaaS). At the highest level of services providing in the cloud we find Software as a Service. It is easier to understand, since it is the stratus that we find closest to the business needs, and therefore farthest from the technical stuff. It can be easily understood with these examples: Office 365 or Gmail.