Principles, Methodology and Tools for Engineering Cloud Computing Systems

1. Introduction: Cloud System Principles And Implications For The Market

Following a quite comprehensive and often cited definition, Clouds can be described as follows: “Clouds are a large pool of easily usable and accessible virtualized resources (such as hardware, development platforms and/or services). These resources can be dynamically reconfigured to adjust to a variable load (scale), allowing also for an optimum resource utilization. This pool of resources is typically exploited by a pay-per-use model in which guarantees are offered by the Infrastructure Provider by means of customized SLAs” (Vaquero et al. 2009).

Cloud Services can be divided into three major areas. Within these areas each service should fulfill the characteristics above. As many companies bundle their offers and put their own description behind them, the boundaries of provided services are not always sharp. Nevertheless, a general understanding in the community has been established that these are the main areas of Cloud Computing services/product that are offered on the market (also see Figure 1):

Figure 1.

Cloud supply chain

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  At its most basic level Infrastructure-as-a-Service (IaaS) delivers resources like prepackaged sets of e.g. CPU and RAM. Virtualized system images can be uploaded to a cloud provider who provides placement and execution of these images on physical hardware within their data centers or within a federated cloud infrastructure.

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  Platform-as-a-Service (PaaS) delivers virtualization and scaling of abstracted software packages above the level of the operating system. Packaged applications are usually uploaded to a cloud platform, or directly developed on the cloud platform itself.

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  Software-as-a-Service (SaaS) is perhaps the most common of the ‘as-a-Service’ terms, and describes fully managed applications delivered as a service. Customers do not need to upload server images or software packages. Instead, they rent access to the software which has been created and is maintained by the cloud provider.

The approach described here represents a lifecycle-based methodology that is illustrated with relevant examples from significant and most recent literature and research. A coherent methodology, which could support companies to embrace the Cloud, is still lacking. That has held back progress both on provider and on consumer side. The presented innovative approach, once applied, has the potential to create transparency for the promising IT paradigm of Cloud Computing. To strengthen the proposed approach we apply principles, present a methodology and showcase tools for engineering Cloud Computing systems.

While understanding the basic technical and business features of this new computing paradigm is essential, one has to see the complete picture and understand the implications for the provision of complex Cloud services including components such as networks, machines, infrastructures and software. Therefore, management of the complexity of consuming Cloud services needs to be understood as a supply chain. As an explicit definition for the Cloud Supply Chain (C-SC), we propose the following definition: “A Cloud Supply Chain is two or more parties linked by the provision of Cloud Services, related information and funds” (based on Tsay, A. et al. 1998; Paulitsch, M. 2003).