Information Technology Reference
In-Depth Information
platforms
and
software
build subsequently upon the forerunning level and
are logi-
cally connected as different layers of a Cloud architecture. Regardless of which term
used, this threefold classification of Cloud Computing has become commonplace
(Eymann 2008, Merrill Lynch 2008, O'Reilly 2008, RightScale 2008, Sun 2009a,
Vaquero et al. 2008).
As the delivery of IT resources or capabilities as a service is an important char-
acteristic of Cloud Computing, the three architectural layers of Cloud Computing
are (see also fig. 4.2):
1. Infrastructure as a Service (IaaS)
2. Platform as a Service (PaaS)
3. Software as a Service (SaaS)
Software as a Service
SaaS
Platform as a Service
PaaS
Infrastructure as a Service
IaaS
Horizontal integration
Fig. 4.2:
The 3 layers of Cloud Computing: SaaS, PaaS, and IaaS
In the following subsections, we describe the three layers of Cloud Computing IaaS,
PaaS and SaaS and how they are logically connected to each other.
4.3.2.1 Infrastructure as a Service (IaaS)
IaaS offerings are computing resources such as processing or storage which can be
obtained as a service. Examples are Amazon Web Services with its Elastic Compute
Cloud (EC2) for processing and Simple Storage Service (S3) for storage and Joyent
who provide a highly scalable on-demand infrastructure for running Web sites and
rich Web applications (Sun 2009a). PaaS and SaaS providers can draw upon IaaS
offerings based on standardized interfaces. Instead of selling raw hardware infra-
structure, IaaS providers typically offer virtualised infrastructure as a service. Foster
et al. (2008) denote the level of raw hardware resources, such as compute, storage
