Information Technology Reference
In-Depth Information
13.3.2 Platform as a Service (PaaS)
The PaaS model is to provide a system stack or platform for application
deployment as a service. NIST defines PaaS as follows:
The capability provided to the consumer is to deploy onto the cloud infrastructure
consumer-created or acquired applications created using programming languages
and tools supported by the provider. The consumer does not manage or control the
underlying cloud infrastructure including network, servers, operating systems, or
storage but has control over the deployed applications and possibly application host-
ing environment configurations.
Figure 13.1 shows a PaaS model diagrammatically. The hardware, as well
as any mapping of hardware to virtual resources, such as virtual servers, is
controlled by the PaaS provider. Additionally, the PaaS provider supports
selected middleware, such as a database and Web application server shown
in the figure. The cloud user can configure and build on top of this middle-
ware, such as define a new database table in a database. The PaaS provider
maps this new table onto their cloud infrastructure. Subsequently, the cloud
user can manage the database as needed and develop applications on top
of this database. PaaS platforms are well suited to those cloud users who
find that the middleware they are using matches the middleware provided
by one of the PaaS vendors. This enables them to focus on the application.
Windows Azure, Google App Engine, and Hadoop are some well-known
PaaS platforms. As in the case of IaaS, traditional vendors such as HP, IBM,
and Microsoft offer solutions that can be used to build private PaaS.
13.3.3 Software as a Service (SaaS)
SaaS is about providing the complete application as a service. SaaS has been
defined by NIST as follows:
The capability provided to the consumer is to use the provider's applications run-
ning on a cloud infrastructure. The applications are accessible from various client
devices through a thin client interface such as a Web browser (e.g., web-based e-mail).
The consumer does not manage or control the underlying cloud infrastructure
including network, servers, operating systems, storage, or even individual applica-
tion capabilities, with the possible exception of limited user-specific application con-
figuration settings.
Any application that can be accessed using a Web browser can be consid-
ered as SaaS. These points are illustrated in Figure 13.1. The SaaS provider
controls all the layers apart from the application. Users who log in to the
SaaS service can both use the application and configure the application
for their use. For example, users can use Salesforce.com to store their cus-
tomer data. They can also configure the application, for example, request-
ing additional space for storage or adding additional fields to the customer
data that is already being used. When configuration settings are changed,
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