Modeling Perfect and Minimal Rejuvenation for Client Server Systems with Heterogeneous Load

In the present study a client-server system is considered, which experiences resource degradation as clients' requests increase. Software rejuvenation is performed in order to counteract resource exhaustion. Two different levels of rejuvenation actions are implemented, perfect, and minimal. Moreover the concept of a failed rejuvenation is introduced to model the fact that rejuvenation due to some circumstances cannot be accomplished. As the load of such a system varies from hour to hour but reveals a cyclic behavior from day to day, different rejuvenation policies for each period of the day are proposed using a cyclic non-homogeneous Markov (CNHM) model. As a measure of performance, the steady-state expected downtime cost is considered. Additionally, to set off the need of CNHM modeling, the system is also modeled by a Homogeneous Markov Chain (HMC) and the performance results are compared.