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Cloud computing is a style of computing in which dynamically scalable and often virtualized resources are provided as a service over the Internet. Users need not have knowledge of, expertise in, or control over the technology infrastructure in the "cloud" that supports them.
The concept generally incorporates combinations of the following:
- infrastructure as a service (IaaS)
- platform as a service (PaaS)
- software as a service (SaaS)
- Other recent (ca. 2007–2009) technologies that rely on the Internet to satisfy the computing needs of users. Cloud computing services often provide common business applications online that are accessed from a web browser, while the software and data are stored on the servers.
The term cloud is used as a metaphor for the Internet, based on how the Internet is depicted in computer network diagrams and is an abstraction for the complex infrastructure it conceals.
The first academic use of this term appears to be by Prof. Ramnath K. Chellappa (currently at Goizueta Business School, Emory University) who originally defined it as a computing paradigm where the boundaries of computing will be determined by economic rationale rather than technical limits.
Brief
Comparisons
Cloud computing can be confused with:
1) grid computing - "a form of distributed computing whereby a 'super and virtual computer' is composed of a cluster of networked, loosely-coupled computers, acting in concert to perform very large tasks".
2) utility computing - the "packaging of computing resources, such as computation and storage, as a metered service similar to a traditional public utility such as electricity" and
3) autonomic computing - "computer systems capable of self-management".
Indeed, many cloud computing deployments as of 2009 depend on grids, have autonomic characteristics, and bill like utilities — but cloud computing tends to expand what is provided by grids and utilities. Some successful cloud architectures have little or no centralized infrastructure or billing systems whatsoever, including peer-to-peer networks such as BitTorrent and Skype, and volunteer computing such as SETI@home.
Furthermore, many analysts are keen to stress the evolutionary, incremental pathway between grid technology and cloud computing, tracing roots back to Application Service Providers (ASPs) in the 1990s and the parallels to SaaS, often referred to as applications on the cloud. Some are of the persuasion that the true difference between these terms is marketing and branding; that the technology evolution was incremental and the marketing evolution discrete.
Characteristics
Cloud computing customers do not generally own the physical infrastructure serving as host to the software platform in question. Instead, they avoid capital expenditure by renting usage from a third-party provider. They consume resources as a service and pay only for resources that they use. Many cloud-computing offerings employ the utility computing model, which is analogous to how traditional utility services (such as electricity) are consumed, while others bill on a subscription basis. Sharing "perishable and intangible" computing power among multiple tenants can improve utilization rates, as servers are not unnecessarily left idle (which can reduce costs significantly while increasing the speed of application development). A side effect of this approach is that overall computer usage rises dramatically, as customers do not have to engineer for peak load limits. Additionally, "increased high-speed bandwidth" makes it possible to receive the same response times from centralized infrastructure at other sites.
Economics
Cloud computing users can avoid capital expenditure (CapEx) on hardware, software, and services when they pay a provider only for what they use. Consumption is billed on a utility (e.g. resources consumed, like electricity) or subscription (e.g. time based, like a newspaper) basis with little or no upfront cost. Other benefits of this time sharing style approach are low barriers to entry, shared infrastructure and costs, low management overhead, and immediate access to a broad range of applications. Users can generally terminate the contract at any time (thereby avoiding return on investment risk and uncertainty) and the services are often covered by service level agreements (SLAs) with financial penalties.
According to Nicholas Carr, the strategic importance of information technology is diminishing as it becomes standardized and less expensive. He argues that the cloud computing paradigm shift is similar to the displacement of electricity generators by electricity grids early in the 20th century.
Although companies might be able to save on upfront capital expenditures, they might not save much and might actually pay more for operating expenses. In situations where the capital expense would be relatively small, or where the organization has more flexibility in their capital budget than their operating budget, the cloud model might not make great fiscal sense. Other factors impacting the scale of any potential cost savings include the efficiency of a company’s data center as compared to the cloud vendor’s, the company’s existing operating costs, the level of adoption of cloud computing, and the type of functionality being hosted in the cloud.
Companies
Vmware, Sun Microsystems, IBM, Amazon, Google, Microsoft and Yahoo are some of the major cloud computing service providers. Cloud services are being adopted by individual users through large enterprises including vmware, General Electric and Procter & Gamble.
Architecture
The majority of cloud computing infrastructure, as of 2009, consists of reliable services delivered through data centers and built on servers with different levels of virtualization technologies. The services are accessible anywhere that provides access to networking infrastructure. Clouds often appear as single points of access for all consumers' computing needs. Commercial offerings are generally expected to meet quality of service (QoS) requirements of customers and typically offer SLAs. Open standards are critical to the growth of cloud computing, and open source software has provided the foundation for many cloud computing implementations.
History
The Cloud is a term that borrows from telephony. Up to the 1990s, data circuits (including those that carried Internet traffic) were hard-wired between destinations. Subsequently, long-haul telephone companies began offering Virtual Private Network (VPN) service for data communications. Telephone companies were able to offer VPN based services with the same guaranteed bandwidth as fixed circuits at a lower cost because they could switch traffic to balance utilization as they saw fit, thus utilizing their overall network bandwidth more effectively. As a result of this arrangement, it was impossible to determine in advance precisely paths traffic would be routed over. The term "telecom cloud" was used to describe this type of networking, and cloud computing is conceptually somewhat similar.
Cloud computing relies heavily on virtual machines (VMs), which are spawned on demand to meet user needs. Because these virtual instances are spawned on demand, it is impossible to determine how many such VMs will run at any given time. As VMs can be spawned on any given computer as conditions demand, they are location in-specific as well, much like a cloud network. A common depiction in network diagrams is a cloud outline.
The underlying concept of cloud computing dates back to 1960, when John McCarthy opined that "computation may someday be organized as a public utility"; indeed it shares characteristics with service bureaus that date back to the 1960s. The term cloud had already come into commercial use in the early 1990s to refer to large Asynchronous Transfer Mode (ATM) networks. Ill-fated startup General Magic launched a short-lived cloud computing products in 1995 in partnership with several telecommunications company partners such as AT&T, just before the consumer-oriented Internet became popular. By the turn of the 21st century, the term "cloud computing" began to appear more widely, although most of the focus at that time was limited to SaaS.
In 1999, Salesforce.com was established by Marc Benioff, Parker Harris, and their associates. They applied many technologies developed by companies such as Google and Yahoo! to business applications. They also provided the concept of "On demand" and SaaS with their real business and successful customers. The key for SaaS is that it is customizable by customers with limited technical support required. Business users have enthusiastically welcomed the resulting flexibility and speed.
In the early 2000s, Microsoft extended the concept of SaaS through the development of web services. IBM detailed these concepts in 2001 in the Autonomic Computing Manifesto, which described advanced automation techniques such as self-monitoring, self-healing, self-configuring, and self-optimizing in the management of
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