EcoFaaS: Rethinking the Design of Serverless Environments for Energy Efficiency

While serverless computing is increasingly popular, its energy and power consumption behavior is hardly explored. In this work, we perform a thorough characterization of the serverless environment and observe that it poses a set of challenges not effectively handled by existing energy-management schemes. Short serverless functions execute in opaque virtualized sandboxes, are idle for a large fraction of their invocation time, context switch frequently, and are co-located in a highly dynamic manner with many other functions of diverse properties. These features are a radical shift from more traditional application environments and require a new approach to manage energy and power. Driven by these insights, we design EcoFaaS, the first energy management framework for serverless environments. EcoFaaS takes a user-provided end-to-end application Service Level Objective (SLO). It then splits the SLO into per-function deadlines that minimize the total energy consumption. Based on the computed deadlines, EcoFaaS sets the optimal per-invocation core frequency using a prediction algorithm. The algorithm performs a fine-grained analysis of the execution time of each invocation, while taking into account the specific invocation inputs. To maximize efficiency, EcoFaaS splits the cores in a server into multiple Core Pools, where all the cores in a pool run at the same frequency and are controlled by a single scheduler. EcoFaaS dynamically changes the sizes and frequencies of the pools based on the current system state. We implement EcoFaaS on two open-source serverless platforms (OpenWhisk and KNative) and evaluate it using diverse serverless applications. Compared to state-of-the-art energy-management systems, EcoFaaS reduces the total energy consumption of serverless clusters by $42 \%$ while simultaneously reducing the tail latency by $34.8 \%$.