Where the structure of any of the three layers is complex, it may be essential to test within the layers to identify sources of performance variations or increased fault risk. This is most likely the case where there is a large geographic scope of users or resources. Conventional testing tools can be used to test servers or network equipment because only the behavior of a single set of resources is being tested, not that of a complex cloud.
A final variable in cloud infrastructure is the "recommission" performance of the cloud -- the time it takes to put something back into service when it's failed. When a resource fails, or when resource scheduling and assignment suggests that an application be moved to an alternative resource to improve overall cloud efficiency, it will be necessary to reload machine images and possibly reconnect internal data paths.
This process is difficult to decompose for testing in a live cloud and is difficult to simulate except with massive load generation. Most operators prefer to use systems management data on virtual machine switchover as a starting point and refine activity and data path monitoring only if they see a consistent issue developing.
Overall, the optimal test strategy for cloud infrastructure is much the same as for testing network infrastructure: Try to test each layer independently; test the boundary conditions; and test the special conditions that form the basis for inter-layer service-level assumptions. That will optimize the skill sets of operations personnel and the existing test and measurement tools.
Tom Nolle is president of CIMI Corporation
This article originally appeared on SearchTelecom.com
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