Cloud Delivery and Hosting Models - Deploying and Managing a Cloud Infrastructure - page 179

sold by private cloud vendors, such as a private cloud infrastructure delivered through public
networks.
Public Cloud A public cloud is any cloud service with an infrastructure that is offered
to the general public that shares its resources. A public cloud is what experts consider to
be the true cloud, with all of its theoretical benefits and features such as affordability,
flexibility, and scalability. This is mainly because of the multitenant model, which allows
the service provider to maximize hardware infrastructure resources and achieve savings
through economies of scale, which in turn allows the service provider to keep on adding
resources to support scalability and the growth of the customers. The public cloud will
always be an off-premises solution.
Hybrid Cloud A hybrid cloud is the combination of both public and private clouds, though
it does not necessarily mean the best of both worlds, or the worst of both, because benefits
will vary depending on how the hybrid solution is implemented. Essentially, a part of the
system will be public in nature and procured from a service provider, such the website and
all of its application. But the other part, the part that requires more security and probably
needs to comply with some special regulations, such as customer data, would have to be
kept in a private on-premises cloud. Banks use this model all the time; the public interface
is through a public cloud, but all customer data remains in-house.
Community A community cloud is a mere application of cloud computing and not so
much an independent cloud computing model. It is essentially an implementation where a
community of entities or organizations makes use of the same cloud environment to facili-
tate better communication and sharing of resources and data. The implementation can be
private (where one of the community members shares the use of its private cloud), public
(where the community makes use of the same public cloud service), or a little bit of both.
On-Premises vs. Off-Premises Hosting Some people confuse on-premises and off-premises
hosting as private or public cloud services, respectively, because they associate private with
in-house and public as the opposite. In fact, private clouds can be hosted both on premises and
off premises as in a private cloud Infrastructure as a Service (IaaS) solution or a co-location
service. Public clouds, on the other hand, are always off premises because the real benefits
of cloud computing can be achieved only through public subscriptions and multitenancy.
On-premises hosting is considered more secure yet more expensive in terms of capital expendi-
tures, while off-premises hosting is considered to have more benefits like flexibility, scalability,
and affordability, but it takes a perceived hit on security and control.
Accountability and Responsibility Based on Delivery Models The cloud adds another
layer of complexity to the delivery of IT services because so many entities are involved.
With this complexity, who is to blame when something goes wrong? For example, if your
provider experiences downtime, it may not be their fault. It may be due to some inherent
problems in the design of a hardware component they use. However, in this case, they must
still answer to their customers, while the manufacturer/distributor of the faulty hardware
will have to answer to the provider.