Algumas definições retiradas do artigo Above the Clouds: A Berkeley View of Cloud Computing
“Cloud Computing refers to both the applications delivered as services over the Internet and the hardware and systems software in the datacenters that provide those services.”
“The services themselves have long been referred to as Software as a Service (SaaS).”
“The datacenter hardware and software is what we will call a Cloud.”
“When a Cloud is made available in a pay-as-you-go manner to the general public, we call it a Public Cloud; the service being sold is Utility Computing.”
“We use the term Private Cloud to refer to internal datacenters of a business or other organization, not made available to the general public.”
“Thus, Cloud Computing is the sum of SaaS and Utility Computing, but does not include Private Clouds. People can be users or providers of SaaS, or users or providers of Utility Computing.”
“When is Utility Computing preferable to running a Private Cloud? A first case is when demand for a service varies with time. (…)A second case is when demand is unknown in advance.”
“Amazon EC2 is at one end of the spectrum. An EC2 instance looks much like physical hardware, and users can control nearly the entire software stack, from the kernel upwards. This low level makes it inherently difficult for Amazon to offer automatic scalability and failover”
“At the other extreme of the spectrum are application domainspecific platforms such as Google AppEngine. AppEngine is targeted exclusively at traditional web applications, enforcing an application structure of clean separation between a stateless computation tier and a stateful storage tier.”
“Applications for Microsoft’s Azure are written using the .NET libraries, and compiled to the Common Language Runtime, a language-independent managed environment. Thus, Azure is intermediate between application frameworks like AppEngine and hardware virtual machines like EC2.”
Oportunidades na utilização de uma infraestrutura de cloud computing
- Mobile interactive applications
- Parallel batch processing.
- The rise of analytics.
- Extension of compute-intensive desktop applications.
- “Earthbound” applications.
Para além destas definições são apresentados também alguns indicadores para avaliar até que ponto pode ser interessante passar para uma infraestrutura de cloud computing, quais os custos operacionais e principais obstáculos previsiveis internos e externos como por exemplo a questão de “Data Lock-in”.
Um ponto que é importante considerar tem a ver com a transferência de grandes volumes de dados e os problemas / custos que podem aparecer quando começamos a pensar em muitos gigas ou terabytes de informação. “Jim Gray found that the cheapest
way to send a lot of data is to physically send disks or even whole computers via overnight delivery services (A conversation with Jim Gray. ACM Queue 1, 4 (2003), 8–17.)”