Page 743 - Cloud computing: From paradigm to operation

XaaS 3

The typical client-server model applications can be easily transformed into custom SaaS applications by
moving servers to the cloud with relatively little modification. The applications suitable for this scenario are
usually developed with special requirements from the enterprise or organization. Top consideration will be
given to security in the system itself, thus the usual way is to group a set of physical machines into a private
zone and to deploy a data management system (which provides abstracted methods of persistence and
operations for different kinds of data) and associated software on it. The system is solely for internal usage
with strict access control. The template of application instance is the same for all customers, and it provides
limited configuration ability. However, the instance for each customer is totally independent of any other
instance.

7.2 Level 2: Configurable SaaS application
For some commonly used applications that are not customized, such as self-service website building system,
SaaS application providers offer common templates for these applications and several sets of run-time
environment for the instances of these applications. Based on the same template, customers are able to
create multiple separated instances of the application by configuring the application's appearance and
behaviour, which are deployed and executed on individual virtual or physical machines to meet their
customized requirements. Application instances are isolated from each other. The architecture is shown in
Figure 3.

Figure 3 – Architecture of configurable SaaS application

The configurable SaaS application has the following characteristics:
1) Application in the initial deployment is a copy of a standard product, and tenants configure the
application to suit their own requirements. However, the configuration options of the product are
limited.
2) For SaaS application providers, any modifications to the product codes can be easily applied to all
tenants immediately. However, only a little update or optimization to the product codes are suitable
for each instance because the forward compatibility problem incurred by the update or optimization
may occur.

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