Information Technology Reference
programming) will be required through the use of the cloud providers' APIs (application
programming interfaces). These are the programming instructions created and offered by the
cloud service providers to those who want to access the functionality of their products.
Currently, some of those APIs are proprietary. This is an issue which will be explored
later when examining some of the limitations and concerns of cloud computing.
However, the notion of providing a wide array of computing-related services on the fly
on a pay-as-you-go basis opens many opportunities for the providers of those services to
exploit this expanding market which (according to Merrill Lynch) is worth 100 billion US
dollars (Buyya, Yeo and Venugopal, 2009). At the same time, it increases the options
available to policy makers entrusted with the job of ensuring the efficient functioning of their
organization's IT resources. On that basis, cloud computing probably represents a paradigm
shift in the way IT, in its all aspects, is being viewed by commoditising it in a manner that
was not possible before (Sultan, 2010).
III. P UBLIC , P RIVATE AND H YBRID C LOUDS
Cloud services, such as those listed above, are known as public clouds when offered by
commercial cloud providers. This is to distinguish them from private clouds, also known as
internal or corporate clouds, where the cloud infrastructure (e.g. data centers, servers etc.) and
services are provided, housed and maintained internally by the users themselves. This is an
example of organizations becoming themselves the providers and consumers of cloud
services. This approach, which might provide organizations with total security and control of
their own resources, actually defeats the whole utility-oriented purpose of cloud computing
which is supposed to guarantee choice, flexibility and cost-effectiveness. In fact, it is doubtful
if this type of arrangement has anything to do with cloud computing as a concept which is
largely utility-based. A number of public cloud providers are now coming up with solutions
which incorporate elements of both private and public clouds that might be classified as
“hybrid clouds”. For example, companies such as Amazon have very recently launched a
service known as Virtual Private Cloud (VPC) designed to address this issue of security and
control which seems to be one of the concerns of large organizations. Amazon's VPC allows
organizations to connect their existing legacy infrastructures to Amazon's clouds via a Virtual
Private Network (VPN) connection 1 . This means that Amazon's cloud customers can create
their own Amazon isolated resources, i.e., virtual private clouds (VPCs) within Amazon's
cloud infrastructure and then connect those resources directly to their network servers using
industry-standard encrypted IPsec VPN connections. In doing so, these customers will be able
to extend their existing security and management policies within their IT infrastructure to
their VPCs as if they were running within their own infrastructures.
1 A virtual private network (VPN) is a private network that provides remote access to its resources through a public
telecommunication infrastructure, such as the Internet.