Cloud Computing and SOA Convergence in Your Enterprise: A Step ...

118 Chapter 6 Working from Your Services to the Clouds
and exposed, we can place them on on-premise or cloud-delivered platforms,
as depicted earlier in Figures 6.1 and 6.2.
Keep in mind that services have the following capabilities within this
type of architecture:
The ability to invoke services as if they were native no matter where they
exist, on-premise or cloud-based, over the local network or the Internet.
The ability to mix and match services within composite applications or
processes, since the interfaces are typically standard (e.g., Web Services
Description Language and Simple Object Access Protocol).
The ability to manage and govern services centrally.
Understanding Coupling for the Clouds
One of the key concepts to consider when talking about services and cloud
computing is the notion of coupling. We need to focus on this because in
many instances, coupling is not a good architectural choice considering that
the services are not only hosted within separate data centers but hosted by
one or more cloud computing providers.
Since the beginning of computing, we have been dealing with the notion
of coupling, or the degree that one component is dependent on another component,
in the domains of both applications and architectures. Lately, the
movement has been toward loose coupling for some very good reasons, but
many architects who build enterprise architectures that leverage cloud computing
understand the motivations behind this because we do not want to become
operationally dependent on a component we do not own nor control.
Breaking this concept down to its essence, we can state that tightly coupled
systems/architectures are dependent on each other. Thus, changes to any one
component may prompt changes to many other components. Loosely coupled
systems/architectures, in contrast, leverage independent components and thus
can operate independently. Therefore, when looking to create an SOA and leverage
cloud computing resources, generally speaking, the best approach is a
loosely coupled architecture.
Keep in mind that how loosely or tightly coupled your architecture exists
is a matter of requirements and not as much about what is popular. Architects
must understand the value of cloud computing and loose coupling and
make the right calls to insure that the architecture matches the business ob-