Admission control of API requests in OpenStack

IaaS clouds have attracted much attention, and OpenStack has become a de facto standard software for building open-source IaaS clouds. However, the performance and scalability of OpenStack services still have room for improvement. This study focused on the admission control of API requests to improve performance. We revealed the basic effect of admission control by setting the concurrent connection limit of API requests in OpenStack, and we confirmed that admission control could improve the performance of OpenStack services by more than 50% in an overloaded situation. We also proposed a heuristic algorithm that adaptively tuned the concurrent connection limit by monitoring the statistics of the completed API requests obtained from a proxy server. Our experimental evaluation revealed that our algorithm helped avoid severe performance degradation in OpenStack.