Cloud Computing Deployment Models

A common misperception about cloud computing is that, eventually, there will be only a handful of cloud platforms, all of which public. This is highly unlikely given the complex ICT needs in large organizations, according to the consulting firm Accenture in its special report “What the Enterprise Needs to Know about cloud computing”

While some general-purpose public clouds will exist, two other types of cloud are likely to emerge. One type, community or speciality clouds will cater to the particular needs of a select group of organizations, an industry or even a country. The healthcare industry is a good example since the inherent nature of medical records underscores the need for clouds to be  non-public so as to ensure data security, while levering mutualized infrastructures to lower ICT costs. Likewise, some large multinationals may opt to build and operate their own private clouds or internal clouds while continuing to tap into external cloud sources. In this way, they can achieve both elasticity and control over service quality, security, data ownership and integrity, and other important regulatory issues. Furthermore, there are applications that simply don't run well in a pure multi-tenant environment. Databases, for example, perform better on dedicated hardware where they don't have to compete for server input/output (I/O) resources. Plus, some businesses prefer to run databases on dedicated hardware for PCI compliance16 reasons or because they do not want sensitive data to reside on a shared platform, even if the environment is highly secure.

Other applications, such as web servers, run well in the cloud because they can use the elasticity of the cloud to scale rapidly. For example, GoGrid Hybrid Hosting gives businesses the option and flexibility of building a secure, high-performance scalable server network for hosting web applications, using a combination of cloud and dedicated server hosting interconnected via a private network link.

Overall, the NIST as well as other practitioners and academics agree to identify four common cloud computing deployment models.

Public Cloud

In simple terms, public cloud services are characterized as being available to clients from a third-party service provider via the Internet. The term “public” does not always mean free, even though it can be free or fairly inexpensive to use. A public cloud does not mean that a user's data is publicly visible; public cloud vendors like Amazon typically provide an access control mechanism for their users. Public clouds provide an elastic, cost-effective means to deploy solutions.

Private Cloud

Private cloud computing—sometimes called Enterprise or Internal cloud computing—is a style of computing where scalable and elastic ICT-enabled capabilities are delivered as a service to internal customers using Internet technologies. This definition is very similar to the definition of public cloud. Hence, the distinction between private cloud and public cloud relates to who can access or use the services in question and who owns or coordinates the resources used to deliver the services (Daryl C. Plummer et al. 2009, p.5). In other words, a private cloud is a cloud that implements the cloud computing model in a private facility where only a single organization has access to the resources that are used to implement the cloud. Therefore, it is a cloud that an organization implements using its own physical resources such as machines, networks, storage, and overall data center infrastructure (Wolsky 2010). A private cloud intends to offer many of the benefits of a public cloud computing environment, such as being elastic and service-based, but differs from a public cloud in that in a private cloud-based service environment, data and processes are managed within the organization for an exclusive set of consumers without the restrictions of network bandwidth, security exposures and legal requirements that public cloud services may entail. In addition, private cloud services are supposed to offer providers and users greater control over the infrastructure, improve security and service resilience because its access is restricted to designated parties. Nonetheless, a private cloud is not necessarily managed and hosted by the organization that uses it as it can be managed by a third party and be physically located off premises, built atop of a public cloud infrastructure or built as a hybrid cloud. In principle, a private cloud assumes a dedicated hardware environment of pooled hardware resources with a virtualization layer running on top of it, allowing an enterprise to create and manage multiple virtual servers within a set of physical servers and charge the organization's business units per usage. According to Gartner in (Bittman 2009, p2), it is envisioned that private  clouds may prevail in the first phases of the cloud computing era whereby many large companies will offload their ICT operations from running their own data and enterprise applications to secure offsite clouds linked to the company's offices through virtual private   networks (VPN) over the Internet. There is some amount of controversy whether a private cloud should be considered as a genuine cloud-based computing environment. For instance, (Armbrust et al. 2009) argues that except for extremely large infrastructures of hundreds of thousands of machines, such as those operated by Google or Microsoft, private clouds exhibit only a subset of the potential benefits and characteristics of public clouds.

There are inherent limitations to consider with private clouds when it comes to elasticity and scaling because the number of virtual machines that can be provisioned is limited by the physical hardware infrastructure. An enterprise can of course add more machines to expand the infrastructure compute power, but this cannot be done as fast and seamlessly as with public clouds. Thus, (Armbrust et al. 2009, p.13) argues not to appoint private clouds as full-fledge cloud computing platforms as this would lead to exaggerated claims. However, they acknowledge that private clouds could get most of the cloud-based computing benefits when interconnected with public clouds through a hybrid cloud-based computing model. The Table below summarizes the key differences between public clouds and private clouds.

Community Cloud

A community cloud is controlled and used by a group of organizations that have shared interests, such as specific security requirements or a common mission. The members of the community share access to the data and applications in the cloud.

Hybrid Cloud

A hybrid cloud is a combination of a public and private cloud that interoperate. In this model, users typically outsource nonbusiness-critical information and processing to the public cloud, while keeping business-critical services and data in their control. The embodiment of hybrid clouds is sometimes found in what is called a Virtual Private Cloud (VPC) whereby a portion of a public cloud is isolated to be dedicated for use by a single entity or group of related entities such as multiple departments within a company. In its simplest form, access to VPC services will be limited to a single consumer and will deliver a service consumption experience that is virtually identical to the public cloud services. VPC services are an emerging phenomenon driven by consumers that are interested in the potential of cloud computing, but who do not want to concede too much control, or share their computing environment with other customers. When combined with a hybrid cloud computing model (for example, using internal resources and external cloud computing services) (Wood et al. n.d.), VPC services have the potential to bridge the gap between public and private cloud models. By providing additional control, management and security beyond that of public cloud services, the VPC approach reduces risks and makes it feasible to deploy a wider range of enterprise applications.

Cloud bursting is a technique used along with hybrid clouds to provide additional resources to private clouds on an as-needed basis. If the private cloud has the processing power to handle its workloads, the hybrid cloud will not be used. When workloads exceed the private cloud’s capacity, the hybrid cloud will automatically allocate additional resources to the private cloud.

All three main cloud providers examined for this study (GoGrid, Amazon and Rackspace) provide some form of hybrid cloud computing services.