Hotspot Mitigations for the Masses

In an IaaS cloud, the dynamic VM scheduler observes and mitigates resource hotspots to maintain performance in an oversubscribed environment. Most systems are focused on schedulers that fit very large infrastructures, which lead to workload-dependent optimisations, thereby limiting their portability. However, while the number of massive public clouds is very small, there is a countless number of private clouds running very different workloads. In that context, we consider that it is essential to look for schedulers that overcome the workload diversity observed in private clouds to benefit as many use cases as possible. The Acropolis Dynamic Scheduler (ADS) mitigates hotspots in private clouds managed by the Acropolis Operating System. In this paper, we review the design and implementation of ADS and the major changes we made since 2017 to improve its portability. We rely on thousands of customer cluster traces to illustrate the motivation behind the changes, revisit existing approaches, propose alternatives when needed and qualify their respective benefits. Finally, we discuss the lessons learned from an engineering point of view.