Cloud Delivery and Hosting Models - Deploying and Managing a Cloud Infrastructure - page 178

Public clouds, on the other hand, are always hosted off premises because, as the name sug-
gests, they are open to the general public. In this model, a cloud service provider provides the
infrastructure as well as the virtualized environments, complete with orchestration and other
platform-specific functions, while at the same time employing multitenancy to maximize the
use of resources. However, this poses some valid security concerns, especially if the multi-
tenancy has not been implemented properly. This might lead to users unexpectedly having
access to the networks and data of other users. To mitigate this problem, network isolation
and user isolation are applied so that each user will see only their own network and data, as
if they are the only ones using the system. This offers economy of scale for the provider and
allows the provider to constantly add hardware infrastructure for added resources in order to
cope with customer demand. It also allows scaling, a major selling point of cloud computing.
Compliance issues are among the concerns about this model since some countries have special
compliance requirements (for example, data belonging to a certain country and its people
must stay within the borders of that country). There is no single way to isolate data for each
user because it would mean reimplementation of the cloud platforms. Organizations with
similar compliance requirements have to resort to private or hybrid solutions, which offer a
little bit of both worlds.
The hybrid cloud model is essentially a combination of both private and public cloud
solutions. As long as there is one aspect of the organization's system that is being conducted
in a private cloud environment and another in a public cloud environment, the system can
be called a hybrid. A good example for this is a company that deals with a lot of customers
with sensitive financial information and data that has to be kept under close surveillance;
the company places the data in-house in an on-premises private cloud while the user portals
and other publicly accessible applications are being offered through a public cloud service.
A community model is more of an application of one or more of the delivery and hosting
models. It is essentially a cloud that is being shared by different organizations to facilitate
faster communication and sharing of data and resources. Oftentimes, this is done through
a public cloud service, but if the collaboration is secretive, such as classified research of
company secrets, then the cloud can be a private one owned by one of the collaborators,
probably the biggest one. As with any system, this can be implemented using a hybrid
cloud, with sensitive information kept in a private cloud and the interface between commu-
nity members accessed through a public cloud or application.
Chapter Essentials
Private Cloud The private cloud is a type of cloud deployment model that is dedicated to
serving a single entity or organization. It does not fully realize all of the benefits of true
public computing but also does not fall into the same traps. This model is appropriate for
those that can afford and really require the added security and those that have special com-
pliance requirements. However, a private cloud solution is not necessarily on premises. A
private cloud can also be an off-premise solution, such as co-location services and solutions