@proceedings {250,
	title = {Workload-Based Software Rejuvenation in Cloud Systems},
	journal = {IEEE TRANSACTIONS ON COMPUTERS},
	volume = {62},
	year = {2013},
	pages = {1072{\textendash}1085},
	abstract = {<p>Cloud Computing is a promising paradigm able to rationalize the use of hardware resources by means of virtualization. Virtualization allows to instantiate one or more virtual machines (VMs) on top of a single physical machine managed by a virtual machine monitor (VMM). Similarly to any other software, a VMM experiences aging and failures. Software rejuvenation is a proactive fault management technique that involves terminating an application, cleaning up the system internal state, and restarting it in order to prevent the occurrence of future failures. In this work, we propose a technique to model and evaluate the VMM aging process and to investigate the optimal rejuvenation policy that maximizes the VMM availability under variable workload conditions. Starting from dynamic reliability theory and adopting symbolic algebraic techniques, we investigate and compare existing time-based VMM rejuvenation policies. We also propose a time-based policy that adapts the rejuvenation timer to the VMM workload condition improving the system availability. The effectiveness of the proposed modeling technique is demonstrated through a numerical example based on a case study taken from the literature.</p>
},
	keywords = {cloud computing, Dynamic Availability, Kronecker algebra, phase type distributions, Time-based Rejuvenation},
	doi = {10.1109/TC.2013.30},
	author = {Bruneo D. and Distefano S. and Longo F. and Puliafito A and Scarpa M}
}
@proceedings {255,
	title = {Software Rejuvenation in the Cloud},
	journal = {Proceedings of the 5th International ICST Conference on Simulation Tools and Techniques (SIMUTOOLS 12)},
	year = {2012},
	month = {23 marzo 2012},
	pages = {8{\textendash}16},
	publisher = {ICST},
	abstract = {<p>In this paper, we investigate how software rejuvenation can be used in a Cloud environment to increase the availability of a virtualized system composed of a single virtual machine monitor (VMM) on top of which a certain number of virtual machines (VMs) can be instantiated. We start from the assumption that the aging of a VMM increases with the number of VMs it is managing, thus characterizing the problem in terms of dynamic reliability. Therefore, by identifying the age of the VMM with its reliability and based on the conservation of reliability principle, we characterize the time to failure of the VMM through continuous phase type distributions. The system availability is thus modeled by an expanded continuous time Markov chain expressed in terms of Kronecker algebra in order to face the state space explosion and to keep memory of the age reached by the VMM in case the number of the hosted VMs change. Time-based rejuvenation is taken into consideration and the optimal timer is evaluated in order to maximize the VMM availability.</p>
},
	keywords = {cloud computing, Dynamic Availability, Phase Type Distributions., Rejuvenation, Virtualized Environments},
	author = {Bruneo D. and Longo F. and Puliafito A. and Scarpa M. and Distefano S.}
}
