1 Introduction
High energy consumption and performance variability problems are two major challenges in modern cloud data centers, as they greatly affect operational expenses, total cost of ownership and revenue [1]. Global data center electricity usage accounted for 1.1-1.5 percent of total electricity use in 2010 [2] and increases at yearly rate of 2.1 percent [3]. As most data centers rely on fossil fuels as their main energy source, huge energy consumption also results in high carbon emissions and environmental concerns. However, according to a recent report by Shehabi et al. in 2016 [4], a potential of 45 percent reduction in electricity demand of data centers can be achieved compared to current trends, by improving their energy efficiency. Moreover, for the significantly large data centers, hardware failures and software anomalies are more frequent, leading to application performance variability and, eventually, Quality of Service (QoS) degradation [5].