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When a computing solution is outfitted with these essential components, it is a cloud solution, and offers significant advantages to users. Most vendors and service providers who operate in the cloud adhere to this definition, perhaps fudging emphasis slightly to fit their solution.

David Frattura, senior director, strategy-cloud solutions for Alcatel-Lucent, simplified the definition. "Cloud means I have the dynamic ability to consumer IT resources where it makes the most sense," Frattura says. "From a provider point of view, I can allocate resource for other customers when in not use."

If the business needs and the cloud service are properly matched, the impact to businesses of this model are profound, says Duane Edwards, SVP Product Development at Globys. "Instead of licensing a software package, acquiring the necessary hardware, and paying consultants to get it all up and running, a business can subscribe to a cloud service and be using it the same day for a fraction of the time, effort, and cost. And if it doesn't meet their needs, they can unplug it without the loss of that same investment in time, effort, and cost."

Service Types

This is where we get into -as-a-Service, or XaaS. In general, there are three types of cloud services.

Software-as-a-service (SaaS): In a recent white paper, Gartner defined SaaS as "software that's owned, delivered and managed remotely by one or more providers. If the vendor requires user organizations to install software on-premises using their infrastructure, then the application isn't SaaS." SaaS offerings are often broken into three categories, explained Nava Levy, vice president, SaaS/Cloud Solutions from cVidya. "1. Employee productivity apps – as web conferencing and e-mail. 2. IT-centric apps as security as a service, and back-up as a service. 3. Enterprise Software apps as CRM and HRM." Examples: Dropbox, GoogleApps, Microsoft Office365, SalesForce.com

Platform-as-a-service (PaaS): "This type of service is a computer platform abstracted from the underlying infrastructure," John Landau, senior vice president of global managed services at TATA Communications explained. "The customer develops and deploys their script-based application—such as java, .net, PHP - on a self-scaling platform, abstracted by the PaaS software from the underlying configuration and low-level infrastructure software." The user has control over applications deployed and perhaps configuration settings, but cannot provision network components, like processing and storage. Examples: Microsoft Azure, Google AppEngine, Heroku. Infrastructure-as-a-Service (IaaS): Forrester research outlays four core components of an IaaS offering: self-service, standardization, automation, and pay-per-use. IaaS typically provides storage, servers, network, and security data center infrastructure on demand to a customer, and the customer owns the deployment, configuration and operation of the platform and applications software. Examples: Amazon EC2, Tata InstaCompute, Verizon (Terremark).

Deployment Models

Generally speaking, there are three deployment models that are of interest; Public, Private, and Hybrid. (The NIST definition describes an additional fourth deployment model, community, but that's a bit outside of our scope.)

• Public: In a public cloud, resources (servers, storage, network, computing) are shared and provisioned across multiple users. The public cloud is generally less expensive for this reason. The most popular public cloud is Amazon Web Services EC2, and for this reason, most public cloud offerings integrate with the Amazon service. Despite attractive pricing, many public cloud offerings aren't replete with the kinds of measures needed to meet enterprise-level security and compliance requirements.


• Private: One cloud, one customer—that's the easiest way to explain private cloud. In a private cloud, the infrastructure is provisioned for one, individual customer. The management of said infrastructure might be handled by a third-party (perhaps the cloud provider itself). Most large enterprises choose private solutions for the amount of control they can retain. All private cloud solutions today, at their heart, are IaaS solutions, says Forrester research. Why? Because by definition they give the customer control of configuration and operation of their applications platform.


• Hybrid: As you might imagine, hybrid cloud is a mix of public and private, so resources are provisioned in both across a public environment, and privately. This is sometimes used to balance loads between clouds when demand reaches critical levels. Other times it refers to when a vendor outsources a portion of the cloud services to the public cloud. Hybrid cloud claims to offer the best of both worlds—the price and rapid scalability advantages of the public cloud and the private security required for mission critical systems.