Section: New Results
Modeling and control of web servers
This work focuses on the design of a server model, the design of admission control laws that allow the server to satisfy different Service Level Objectives, and the implementation of the latter. This work is in collaboration with Sardes team at INRIA.
The first part of the work consists in designing a continuous time model using a fluid flow approach. Inherent non-linearities of such systems are taken into account. We validate model with different experimental data sets, under different conditions. Results show the relevancy of the model, which is accurate on a wide range of load.
Then it is used for control purposes. We build theoretical admission control laws that ensure a compromise between performance and availability of the system. We implemented them on a real system which is supposed to emulate an e-business environment  , . Fig. 10 show the behaviour of the closed loop system when a sudden increase of the workload amount occurs. The control law implemented here was designed to prevent the average latency of the requests from exceeding a given Lmax while maximizing the availability of the system. This work is under patent  .