As cloud computing becomes more mainstream, there seems to be an exponential increase in the number and variety of definitions of the technology. Does cloud computing mean Internet services? Grid computing? Web 2.0? On-demand computing? Software as a service? All of the above? Some say it is simply any computing capability that takes place outside the firewall.
Unfortunately, many of the current definitions of cloud computing are self-serving, needlessly dogmatic and even misleading. As multiple vendors, service providers, consultants and others with vested interests define cloud computing primarily to advance their own commercial agendas, enterprises should be wary of these definitions.
In an effort to clarify, the National Institute of Technology and Standards (NIST), a non-regulatory arm of the Commerce Department, recently developed its own definition of cloud computing that will serve as a foundation for the federal government’s use of cloud models, architectures and deployment strategies.
Peter Mell and Tim Grance, authors of the NIST definition, describe cloud computing as “a model for enabling 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.”
According to Mell and Grance, cloud computing comprises the following five essential characteristics:
On-demand self-service. A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed without requiring human interaction with each service’s 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, laptops and PDAs).
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 data center). Examples of resources include storage, processing, memory, network bandwidth and virtual machines.
Rapid elasticity. Capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out, and rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time.
Measured Service. Cloud systems automatically control and optimize resource use by leveraging a metering capability 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.
NIST further describes three distinct service models:
Cloud Software as a Service (SaaS). The capability provided to the consumer is to use the provider’s applications running on a cloud infrastructure. The applications are accessible from various client devices through a thin client interface such as a Web browser (e.g., Web-based e-mail). The consumer does not manage or control the underlying cloud infrastructure or even individual application capabilities, with the possible exception of limited user-specific application configuration settings.
Cloud Platform as a Service (PaaS). The capability provided to the consumer is to deploy onto the cloud infrastructure consumer-created or acquired applications using programming languages and tools supported by the provider. The consumer does not manage or control the underlying cloud infrastructure but has control over the deployed applications and possibly application hosting environment configurations.
Cloud Infrastructure as a Service (IaaS). The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls).
NIST also describes four different deployment models for cloud computing:
Private cloud. The cloud infrastructure is operated solely for an organization. It may be managed by the organization or a third party and may exist on premises or off premises.
Community cloud. The cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy and compliance considerations). It may be managed by the organizations or a third party and may exist on premises or off premises.
Public cloud. The cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services.
Hybrid cloud. The cloud infrastructure is a composition of two or more clouds (private, community or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load-balancing between clouds).
Mell and Grance stipulate that cloud computing is an evolving technology and that definitions, attributes and characteristics will continue to evolve and change over time. Nonetheless, their work is significant because it represents the de facto standard definition for the U.S. government — the single largest IT consumer on the planet with an annual IT budget of nearly $80 billion.
