Separating internal and external fluctuation in distributed web-based services

The observable behavior of a complex system reflects the mechanisms governingthe internal interactions between the system’s components and the effect ofexternal perturbations. We investigate the behavior of a distributed system providingWeb-based services and the effects of the impact of external request arrivals on theinternal system resources; the results of our study are of primary importance for takingseveral runtime decisions on load and resource management. Here we show that bycapturing the simultaneous activities of several performance indexes of the Web-basedsystem nodes we can separate the internal dynamics from the external fluctuations. Forevery internal performance index, we are able to determine the origin of fluctuations,finding that while all the considered performance indexes of the application server haverobust internal dynamics, the CPU utilization and the network throughput of the Weband database servers are mainly driven by external demand.