Cloud Computing

Cloud computing refers to a utility-based provisioning of virtualized computa-tional resources over the Internet.

Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model is composed of five essential characteristics, three service models, and four deployment models.

Essential Characteristics:

On-demand self-service: A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.

Broad network access: Capabilities are available over the network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, tablets, laptops, and workstations).

Resource pooling: The provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand. There is a sense of location independence in that the customer generally has no control or knowledge over the exact location of the provided resources but may be able to specify location at a higher level of abstraction (e.g., country, state, or datacenter). Examples of resources include storage, processing, memory, and network bandwidth.

Rapid elasticity: Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be appropriated in any quantity at any time.

Measured service: Cloud systems automatically control and optimize resource use by leveraging a metering capability1 at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer of the utilized service.

On-Premise Computing:

• Requires hardware, space, electricity, cooling
• Requires managing OS, applications and updates
• Software Licensing
• Difficult to scale:
  • Too much or too little capacity
• High upfront capital costs
• You have complete control

Cloud Computing:

• Shared, multi-tenant environment
• Pools of computing resources
• Resources can be requested as required
• Available via the Internet
• Private clouds can be available via private WAN
• Pay as you go

Una de las ventajas más importantes del Cloud es que puede ser «scaled» fácilmente (Resources can be requested as required). En otras palabras, a través del cloud la capacidad se puede variar fácilmente con respecto a la demanda. sólo cuando la demanda sea alta, el sistema será configurado para disponer de gran capacidad. On-Premise Computing, lo que generalmente pasa es que se configura el sistema para cubrir una capacidad promedio y generalmente se debe sobreestimar para que, cuando la demanda sea alta, poder todavía cubrirla. Entonces, cuando la demanda es baja estamos a "over capacity" y podría también pasar que cuando la demanda sea muy alta estemos a "under capacity". Esto es solucionado en el cloud. Esto se puede visualizar a través del ejemplo presentado en las siguientes figuras, en el cual se plantea el caso de un Concert ticket web site.

Infrastructure as a Service (IaaS) - Platform as a Service (PaaS) - Software as a Service (SaaS)

Cloud: IaaS - PaaS - SaaS: En esta gráfica se puede ver que la Virtual machine corre directamente sobre el hardware.. No hay un SO sobre el cual corren las VM's