Information Technology Reference
In-Depth Information
4.3 Architecture and Components of Clouds
In this section, we first provide an overview of concepts regarding the structure and
components of Clouds. Then, we describe the most cited three-layer architectural
concept for Clouds in detail.
4.3.1 Overview of Existing Concepts for Cloud Structures and Components
It is possible to find a number of concepts for Cloud structures in literature. At
first sight, these classifications appear to differ from each other to varying extent.
Eventually, however, they classify and describe the same phenomenon and share a
common denominator.
Menken (2008) provides a very detailed concept consisting of 7 major compo-
nents of Cloud Computing, namely application, client, infrastructure, platform,
service, storage, and processing power. Miller (2008) looks at “different ways a
company can use cloud computing to develop its own business applications”,
and distinguishes four types of Cloud service development, namely Software as
a Service, Platform as a Service, Web Services, and On-Demand Computing.
On-Demand Computing, as Miller (2008) notes, is also referred to as utility
computing. Youseff et al. (2008) distinguish five layers of Cloud Computing: Cloud
application, Cloud software environment, Cloud software infrastructure, software
kernel, and firmware/hardware.
Forrester Research relate the components of Clouds to markets and distinguish
five Cloud services markets. Two of them, Web-based services and SaaS offerings,
are reported to be known markets that are delivered from the Cloud, whereas three
cloud-infrastructure-as-a-service markets are new: app-components-as-a-service,
software-platform-as-a-service, and virtual-infrastructure-as-a-service (Gilles et
al. 2008). Finally, Reese (2009) considers SaaS as the term for “software in the
cloud” and distinguishes four Cloud Infrastructure Models, namely Platform as a
Service, Infrastructure as a Service, Private Clouds, and a fourth model representing
all aspects of the previous Cloud infrastructure models.
All of the concepts above are very detailed and are influenced by the specific
perspective on Clouds the respective authors take. Some of the concepts also involve
aspects as Private Clouds and have different levels of detail for components that
make up one logical entity. Given this, the concepts above do not provide a suffi-
ciently generic description of a Cloud structure and its components. The concept
most commonly used to describe a generic structure and components of Clouds is a
3-layered concept, which will be described in more detail in the next section.
4.3.2 The Three Layers of Cloud Computing
The definitions provided in section 4.2 already show that Cloud Computing comprises
different IT capabilities, namely
infrastructure
,
platforms
and
software
. This may
also be referred to as different 'shapes', 'segments', 'styles', 'types', 'levels' or
'layers' of Cloud Computing. Instead of speaking of different 'capabilities',
thinking of it as different 'layers' makes much more sense because
infrastructure
,
