QoS-Oriented Service Computing - Advanced Design Approaches to Emerging Software Systems - page 282

perspective emphases the use of virtualisation
technology in the Cloud computing. Virtualization
technologies multiplex hardware and have made
the flexible and scalable provision of resource as
hardware and software on demand easier. Virtual
machine techniques, such as VMware (http://www.
vmware.com/) and Xen (http://www.xen.org/),
offer virtualized IT-infrastructures on demand.
Virtual network advances, such as VPN (Virtual
Private Network), support users with a customized
network environment to access Cloud resources.
Cloud service or Cloud Computing? - Apart
from the above perspectives about the Cloud
computing, we think it would be more accurate
to call it “Cloud service”, rather than using the
term “Cloud computing”, as eventually everything
delivered by Cloud is presented as a Web service,
e.g. storage service, computing service.
Currently many research and development
work relating to Cloud computing focus on
single provider Cloud within an administrative
domain. This single provider Cloud has inherently
problems of scalability and interoperability. For
example, the single provider may not be able to
provide infinite scalability. Also, this can result in
an inability to scale through business partnerships
across Clouds providers. Customer has to lock to
a single Cloud vendor and no flexibility to choose
Cloud vendors. More recently, “federated Cloud
computing” is emerging. There is no global defini-
tion for federated Cloud computing but the aim
of the federated Cloud computing is to federate
disparate data centers, including those owned by
separate organizations to enable a seemingly infi-
nite service computing utility (Rochwerger et al.,
2009). So far there is not much effort in research
and development of federated Cloud computing.
An EU FP7 funded project RESEVIOR (http://
www.reservoir-fp7.eu/) is currently investigat-
ing this and proposed a RESEVIOR model and
architecture for open federated Cloud computing
(Rochwerger et al., 2009). In this RESEVOIR
model the entity of “service providers” and “infra-
structure providers” are clearly differentiated. The

“service providers” understand customer needs
and offer associated services to address customer
needs. But “service providers” do not own any
computational resources by themselves; instead,
they rent resources from “infrastructure provid-
ers” for service applications. The computational
resources of each infrastructure provider (called
“site” in RESEVOIR model) are partitioned by a
virtualization layer into several Virtual Execution
Environments (VEE). The federation of sites forms
a RESEVOIR Cloud, where a service application
will be deployed. The service application can be
regarded as consisting of a set of software com-
ponents working together to achieve a goal. Each
component of such service applications executes
in a certain VEE. These VEEs can be placed on
the same or different VEE Hosts within the site, or
even on different sites. The EU-funded Edutain@
Grid project (http://www.edutaingrid.eu/) has also
proposed a federated Cloud computing model with
associated business infrastructure for real-time
online interactive applications, where multiple
independent infrastructure providers can cooperate
seamlessly to provide scalable IT infrastructure
and QoS-assured services. The distinct feature
of Edutain federation Cloud computing model is
that it lies in the concept of “code mobility”. More
about Edutain federated Cloud computing model
can be found in the section “Case Study: QoS-
oriented Service Computing in Edutain@Grid”.

QOS-ORIENTED SERVICE
COMPUITNG

The SPI model of Cloud computing determines that
service is a fundamental construction unit. How-
ever, the traditional service computing usually
focuses on the functional aspects of a service such
as service modeling, service composition, etc. In
order to accommodate the need for bringing SOA
in Cloud computing, we proposed QoS-oriented
service computing which aims to address the fol-
lowing major issues: (i) Service Level Agreement