What is cloud computing?

Cloud computing is a business model of delivering IT resources such as computing power, storage, memory, networking, software and application development platforms "as a service."

Gartner defines five attributes of cloud computing: service-based, scalable and elastic, shared, metered by use, uses internet technologies. That's why virtualization has become a core enabler of cloud computing because it allows the optimal use of IT resources, consolidating them in an efficient and flexible shared infrastructure to deliver scalable and elastic cloud services.

In the same way we consume electricity and other utilities today, subscribers to cloud computing services pay for only what they use and access the services from any web browser running on a desktop computer, a laptop or even a mobile device like a smartphone or a tablet.

For enterprise IT, that means a shift from high upfront capital expenditure (capex) to an operational expenditure (opex) model with measurable business value through provisioning and billing capabilities. The elasticity, scalability and the pay-as-you-go cloud model also create the need for service providers and enterprises to embrace best practices, set clear service level agreements and fulfill them.

Three categories of cloud computing service

The three main categories of cloud service are infrastructure-as-a-service, platform-as-a-service and software-as-a-service.
  • Infrastructure-as-a-service or IaaS is the provisioning of equipment such as storage, hardware, servers and networking components as a service. Some service providers have touted their services as security-as-a-service, desktop-as-a-service, communication-as-a-service and even anything-as-a-service (XaaS).
  • Platform-as-a-service or PaaS is the provisioning of networks, servers and storage as well as application development tools and libraries for the design, development, testing, deployment and hosting of applications. PaaS providers typically also integrate application services such as collaboration, web services, on-demand scalability, versioning, database integration and community facilitation.
  • Software-as-a-service or SaaS is the delivery of business applications such as finance and accounting, customer relationship management, enterprise resource planning, human resource management, content management and office productivity tools. Application performance monitoring and application delivery vendors have also updated their solutions for the cloud.


Three cloud computing deployment models

  • The private cloud -- enterprise IT may buy, build and deliver its cloud services or engage a third-party provider to do that. The private cloud is either hosted on-premise behind the corporate firewall or hosted off-premise on multi-tenant or dedicated servers. Businesses adopting the private cloud have the ability to manage security and allocate resources, and where applicable, ensure compliance with relevant industry and government requirements and regulations.
  • The public cloud -- any individual from the general public, including corporate employees, may subscribe to applications, storage or other resources for free or by paying a fee monthly or on a pay-per-use basis. An off-premise service provider hosts and manages these cloud services and delivers them over the Internet to subscribers. For enterprise IT, the public cloud offers the ability to scale up quickly and cost-effectively but security risks make it unsuitable for mission-critical business applications.
  • The hybrid cloud -- enterprise IT provides and manages some cloud services from a private cloud and subscribes to some services from an off-premise third-party public cloud provider. Enterprises can mix and match resources between local infrastructure or the private cloud and the public cloud, scaling and provisioning resources on demand; spreading application and data workloads; and federating security policies across clouds.
An industry term that has been gaining airtime is the 'personal cloud'. Forrester believes that "digital devices and services will combine to create the personal cloud, an integrated resource for organizing, preserving, sharing, and orchestrating personal information and media." Still, the deployment model for the personal cloud could be public, private or hybrid.


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