chapter discusses cloud computing technology and cloud models. As an example of a public
cloud we consider Amazon Web Services (AWS), and for a private cloud VMWare cloud
technology. These providers hold most of the market share in their specific niches, and are worth
2.1 An Introduction to Cloud Architecture
As the introduction notes, the idea of providing centralized computing services over a network is
not new – mainframe timesharing technology was popular as far back as the 1960s, but was
replaced by personal computers and client-server architecture. Until around 10 years ago, typical
enterprise computing infrastructure consisted of powerful and very expensive servers.
Infrastructure architecture was monolithic, and each of these powerful machines could easily
host 20-30 enterprise applications. This market was dominated by only a few hardware vendors,
such as IBM, Sun, HP, and Dec, whose servers were expensive to purchase and maintain, took
considerable time to install and upgrade, and in some cases were vulnerable to server outages
that could last several hours until a vendor representative delivered proprietary replacement
The operating system was installed directly to hardware, and most of the servers hosted multiple
applications within the same operating system without providing physical or virtual isolation (see
Figure 1). Because it was difficult to quickly move and rebalance applications across servers,
server resources were not utilized most effectively.
Distributed applications, which were installed over multiple servers, communicated with each
other using CORBA or DCOM communication protocols over RPC. However, it was a major
problem with such protocols that they were vendor-dependent, and so the implementation of one
vendor might not be compatible with that of others. This was solved at the beginning of the
2000s by the introduction of web services, which use open specifications that are language,
platform, and vendor agnostic. 


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