An Investigation on Data Center Cooling Systems Using FPGA-based Temperature Side Channels

As power and cooling cost has become a major factor in the total cost of ownership (TCO) of large-scale data centers, it is important to investigate how data centers run their cooling systems in practice. The data centers of Amazon Web Services (AWS) have been continuously expanding worldwide, and their restrictive security policies keep many management aspects of data centers private. In this paper, we make an attempt to explore the cooling systems of AWS data centers without privileged accesses. We first demonstrate PVT (process, voltage, and temperature) variations in AWS FPGAs (Field Programmable Gate Arrays) using time-digital converters (TDC). We further leverage the DRAM temperature side channel and improve the usage of the TDC to measure the temperature change accurately. We conduct a measurement on the daily temperatures of AWS data centers worldwide and find that temperature changes of some data centers are closely related to local weathers. Thus, we deduce they adopt free cooling techniques. This measurement study motivates us to re-think the vulnerability of data centers to power/thermal attacks.