Information Technology Reference
In-Depth Information
2.4
Consequences
Considering the primary characteristics of clouds, it is obvious that full exploitation of
the capabilities is tied to the use cases, even though the principle allows for a broader
scope with the implicit loss of performance, respectively quality of service. Clouds
are often treated as the panacea of IT, but they are effectively specialised domains, so
that outside of this domain other environments show better performance.
These domains, however, cannot be easily specified along the line of “eScience”,
“business applications” or similar. Rather, they deal with specific immediate
requirements (availability, elasticity etc.), thus allowing for a wide scope of use cases
all following under “utility computing”. But similarly, “eScience” or “business
applications” cannot easily be translated into one specific IT domain either.
We can note, which conditions the application should fulfil in order to be able to
exploit the cloud, respectively to benefit from it in the first instance - these are:
•
Dynamic number of users, respectively requests
•
Small and infrequently shared data between a limited number of instances
•
Communication between instances and data sharing is primarily asynchronous
•
Comparatively low scale of the application itself (i.e. degree of parallelism)
As noted, many of these conditions can be seen as comparatively “lax” boundaries,
i.e. they allow for a certain degree of freedom - e.g. synchronous messages are
certainly possible, if the delay is not crucial for the execution of the application. We
can however also denote hard boundaries that cloud systems cannot fulfil and
therefore constrain the scope of usage:
•
Single instance applications simply do not benefit from cloud management
Data intensive applications where performance is crucial
•
•
Large scale applications which require a large amount of resources for fulfilling
their work. Notably, they might run on the cloud, depending on their
communication dependency, but they do not exploit the essential cloud capabilities
•
Applications where execution performance is crucial and where performance is
influenced by any communication related overhead, including instantiation
3
Classifying Your Application
As elaborated in the preceding chapter, clouds are constrained in their applicability
scope and many use cases either do not benefit from the additional capabilities offered
by the cloud, or even suffer from its limitations. It has also become obvious though,
that it is not easy to classify an existing application or use case for its potential
benefits from cloud environments. Most of the core characteristics identified in the
preceding section may be hidden within the application, i.e. it requires real in-depth
expertise of the application to identify it. What is more, it is not clear whether the
according constraints could not be overcome by changing the code (see next section).
Here we provide a set of criteria that may help in classifying the use case /
application and to assess the potential benefit to be gained from the cloud:
