Within the last years, the increasing presence of large-scale
architectures has introduced the era of Cloud Computing. There
is a huge number of different definitions available towards
Cloud Computing. The term "cloud" itself is derived from the
figurative abstraction of the internet represented as a cloud.
The available definitions of Cloud Computing range from
reductions it to be ``the next hype term" over pragmatic
definitions focusing on special aspects to definitions, that see
Cloud Computing as a general paradigm shift of information
architectures, as an ACM CTO Roundtable [Cre09] has shown in
2009. Of the various features that are attributed to the
"cloud", scalability, a pay-per-use utility model and
virtualization are the minimum common denominators. The key
concept of Cloud Computing is the resourcing of services. These
services can be generally differentiated into three vertical
layers: Referring to the terminology of Cloud Computing, a
scalable web application is essentially a SaaS that requires a