Various cloud deployment models.

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Cloud services can be deployed in different ways, depending on the organizational structure and the provisioning location. Four deployment models are usually distinguished, namely public, private, community and hybrid cloud service usage.

Public Cloud

The deployment of a public cloud computing system is characterized on the one hand by the public availability of the cloud service offering and on the other hand by the public network that is used to communicate with the cloud service. The cloud services and cloud resources are procured from very large resource pools that are shared by all end users. These IT factories, which tend to be specifically built for running cloud computing systems, provision the resources precisely according to required quantities. By optimizing operation, support, and maintenance, the cloud provider can achieve significant economies of scale, leading to low prices for cloud resources. In addition, public cloud portfolios employ techniques for resource optimization; however, these are transparent for end users and represent a potential threat to the security of the system. If a cloud provider runs several datacenters, for instance, resources can be assigned in such a way that the load is uniformly distributed between all centers.

Figure 1: Three users accessing a public cloud

Some of the best-known examples of public cloud systems are Amazon Web Services (AWS) containing the Elastic Compute Cloud (EC2) and the Simple Storage Service (S3) which form an IaaS cloud offering and the Google App Engine with provides a PaaS to its customers. The customer relationship management (CRM) solution Salesforce.com is the best-known example in the area of SaaS cloud offerings.

Private Cloud

Private cloud computing systems emulate public cloud service offerings within an organization’s boundaries to make services accessible for one designated organization. Private cloud computing systems make use of virtualization solutions and focus on consolidating distributed IT services often within data centers belonging to the company. The chief advantage of these systems is that the enterprise retains full control over corporate data, security guidelines, and system performance. In contrast, private cloud offerings are usually not as large-scale as public cloud offerings resulting in worse economies of scale.

Figure 1: A user accessing a private cloud

Community Cloud

In a community cloud, organizations with similar requirements share a cloud infrastructure. It may be understood as a generalization of a private cloud, a private cloud being an infrastructure which is only accessible by one certain organization.

Figure 3: Three users accessing a community cloud

 

 Hybrid Cloud

A hybrid cloud service deployment model implements the required processes by combining the cloud services of different cloud computing systems, e.g. private and public cloud services. The hybrid model is also suitable for enterprises in which the transition to full outsourcing has already been completed, for instance, to combine community cloud services with public cloud services.

Figure 4: Hybrid cloud usage