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and network resources, as the fabric layer. Typically by virtualization, hardware
level resources are abstracted and encapsulated and can thus be exposed to upper
layer and end users through a standardized interface as unified resources (Foster et
al. 2008) in the form of IaaS (see figure 4.3).
Software
Cloud Infrastructure
Cloud Services
Application
Software as a Service (SaaS)
Platform
Platform as a Service (PaaS)
Unified Resource
Infrastructure as a Service (IaaS)
Fabric
Infrastructure
Fig. 4.3:
Cloud Architecture related to Cloud services (adapted from Foster et al. 2008)
Already before the advent of Cloud Computing, infrastructure had been available as
a service for quite some time. This has been referred to as utility computing, which
is also used by some authors to denote the infrastructure layer of Cloud Computing
(e.g. Armbrust et al. 2009, Miller 2008, O'Reilly 2008). Sun, for example, launched
its Sun Grid Compute Utility in March 2006 (Schwartz 2006). The Sun Grid
Compute Utility allowed users to purchase computing capability for $1/cpu-hr,
i.e. on a pay-per-use basis. The Sun Grid Compute Utility could be accessed via
Network.com. One year later, in March 2007, Sun announced the Network.com
Application Catalog, which allowed developers and open source communities
to just “click and run” their applications online (Sun 2007). Two years later, in
March 2009, Sun announced its Open Cloud Platform as well as plans for its Sun
Cloud, whose main services will be the Sun Cloud Storage Service and Sun Cloud
Compute Service (Sun 2009b). Network.com, which once was the access point to
the Sun Grid Compute Utility and the Network.com Application Catalog, was in
a transition mode in early 2009 and now redirects to 'Sun Cloud Computing'(Sun
2009c, Sun 2009d).
Compared to the early utility computing offerings, IaaS denotes its evolution
towards integrated support for all three layers (IaaS, PaaS, and SaaS) within a Cloud
(see also Fellows 2009). From the early offerings of utility computing it became
clear that for utility computing providers to be successful, they need to provide an
interface that is easy to access, understand, program, and use, i.e. an API that would
enable easy integration with the infrastructure of potential customers and poten-
tial developers of SaaS applications. Utility Computing providers' data centres are
sufficiently utilized only if they are used by a critical mass of customers and SaaS
providers.
