Event-Triggered Control Design for Systems With Exogenous Inputs: Application for Auto-Scaling of Cloud-Hosted Web Servers

In this article, an event-triggered control (ETC) law is proposed for auto-scaling of Web servers hosted on a private cloud. The Web server systems are modeled as a discrete-time linear time-invariant (LTI) system where the incoming Web requests act as disturbance inputs. Dealing with such disturbance inputs adds an additional challenge in the design and real-time implementation of the ETC. To address this challenge, we first design an ETC law to ensure ${\mathscr {D}}_{R}$ stability of the nominal system. Second, we derive the conditions which ensure input to state stability of the closed-loop system, under the event-triggered implementation, with respect to disturbance inputs. Then, sufficient conditions are derived, which ensure that the interevent times are nontrivial. Finally, to show the efficacy of the proposed approach, we validate our results on an experimental testbed of a Web server system hosted on a private cloud and provide comparative results.