328
Cloud
Computing
maximum interest of learners of this subject) are built over a stage that can be called as the
platform for cloud. This platform provides the supporting system for cloud operations.
The
platform for cloud computing operations is generally built
over large distributed
homogeneous/heterogeneous computing environments. This underlying layer provides the
support system on which different cloud computing facilities are developed to be delivered over
internetwork/Internet.
Apart from computing devices, this layer (the platform for cloud) also
includes supporting facilities like the power supply system, cooling system,
physical security
of infrastructure and others. The host operating system (operating system that activates the
physical systems at data centers) and hypervisors stay at the top of this layer.
Cloud service layer mainly comprises of three categories of computing services as
infrastructure service, platform service and application service. Among three of these, the
infrastructure service is most interesting. Although, at data centers cloud
infrastructure services
are built using actual physical computing resources, consumers get access to these resources in
virtual form through IaaS facility.
Cloud architectures at data center can be portrayed as a combination of two layers: 1) the
underlying infrastructure for cloud service development, and 2) the layers of services developed
over the infrastructure.
19.2 REVIEWING DESIGN CHARACTERISTICS
The power of cloud computing system is often considered the outcome of combination of
dynamic-elastic infrastructure and
flexible-composable application architecture. In a sense,
the application part gathers its strength from the dynamic nature of underlying computing
infrastructure.
The dynamic infrastructure is built by the systematic application of techniques like resource
pooling,
resource sharing, resource virtualization, dynamic resource provisioning and load
balancing. Flexible system design helps to easily incorporate horizontal
scaling into the system
which is a major strength of cloud computing system. Scalable system resources provide the
elasticity to the system. Among all techniques mentioned here,
resource virtualization has
