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"
Public Cloud", this categorisation has been extended to other deployment
models besides these original forms, such as “Hybrid Cloud” or even more
specialised forms like “Community Cloud”. The typical distinguishing
features of these types are:
Public Cloud
"
The Cloud" is often used as a synonym of "Public Cloud". According to the
NIST definition:
“
The Cloud infrastructure is provisioned for open use by the general public.
It may be owned, managed, and operated by a business, academic, or
government organisation, or some combination of them. It exists on the
premises of the Cloud provider. “
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This definition implies that Public Clouds are disparate resources by nature,
and give rise to questions of security, law and availability, which we will be
looking at in detail later on in this book. It is important to pay attention to
this, because all the disadvantages or benefits of this deployment model are
often implicitly assumed, therefore preventing an objective discussion of the
proposed solution.
In a Public Cloud an entity’s data is virtually segmented from another
entity’s data while sharing a common IT infrastructure.
Public Cloud can provide a number of services (business processes,
workflows, IT applications and/or IT infrastructures) on a variable
pay‐per‐use basis that are basically open to anybody at the same time
(
multi‐tenant capable) over public networks. Cloud users share the
underlying infrastructure, which is abstracted from the application layer
(
and are either unaware of this fact, or of the scope). In an ideal Cloud‐only
model none of the physical IT resources and infrastructures that support a
specific service are tangible to the user, and all of the relevant applications
reside outside of the enterprise firewall. One of the major distinguishing
features of a Public Cloud is that the user cannot influence who uses the
services offered by the provider (from a technology, or from a contractual
point of view). The options for customising services to meet specific user
requirements are typically very limited, as they conflict with the provider's
scaling and efficiency interests. There is typically no localisation of
resources, or no localisation option, or it is not part of the service
agreement. The owner and operator of a Public Cloud service is typically
called an IT service provider.
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