Obtaining an instance of a cloud computing environment via a
public cloud is easy and inexpensive because hardware,
application, and bandwidth costs are covered by the provider.
Computing resources in a public cloud can be scaled to meet the
needs of the cloud users.
A public cloud can use flexible pricing models. No resources are
wasted because the cloud users pay for what they use on an as-
needed basis, without the requirement to invest in additional
internal infrastructure.
A public cloud helps businesses shift the bulk of the costs from
capital expenditures and IT infrastructure investment to a utility
operating expense model. A public cloud also helps isolate the
end-users from the complexity of IT operations and
management.
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32
Public Cloud
Public cloud or external cloud describes cloud computing in the
traditional mainstream sense, whereby resources are
dynamically provisioned on a fine-grained, self-service basis
over the Internet via Web applications/Web services. These Web
applications/Web services originate from an off-site third-party
provider who shares resources and bills on a fine-grained utility
computing basis.
Public clouds are where IT activities/functions are provided "as a
service" over the Internet, which allows access to technology-
enabled services without knowledge of, expertise with, or control
over the technology infrastructure that supports them. Therefore,
public clouds are also called "external clouds".
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Private Cloud
Private cloud and internal cloud are neologisms that some
vendors have recently used to describe offerings that
emulate cloud computing on private networks. These
(typically virtualization automation) products claim to
"deliver some benefits of cloud computing without the
pitfalls", capitalizing on data security, corporate
governance, and reliability concerns.
Private clouds are where activities and functions are
provided "as a service" over a company's intranet. Private
clouds are built by an organization for its own users, and
everything is delivered within the organization's firewall
(instead of the Internet). The private cloud owner does not
share resources with any other companies, so multitenancy
is not an issue. Therefore, private clouds are also called
"internal clouds".
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34
Private Cloud
A private cloud is owned by an enterprise and can only be
accessed by internal users.
A private cloud is deployed internally behind the corporate
security firewall.
A private cloud is operated and maintained by either the
enterprise's IT operations or by a 3rd party cloud service
provider.
By totally owning a cloud computing environment, an enterprise
can provide and govern computing resources (physical servers,
application servers, storage space, applications, services, etc.)
in an efficient, compliant, and secure manner. At the same time,
by using a private cloud, an enterprise can also achieve
significant cost saving from the infrastructure's consolidation and
virtualization.
