Locality-aware Load-Balancing For Serverless Clusters

While serverless computing provides more convenient abstractions for developing and deploying applications, the Function-as-a-Service (FaaS) programming model presents new resource management challenges for the FaaS provider. In this paper, we investigate load-balancing policies for serverless clusters. Locality, i.e., running repeated invocations of a function on the same server, is a key determinant of performance because it increases warm-starts and reduces cold-start overheads. We find that the locality vs. load tradeoff is crucial and presents a large design space. We enhance consistent hashing for FaaS, and develop CH-RLU: Consistent Hashing with Random Load Updates, a simple practical load-balancing policy which provides more than 2x reduction in function latency. Our policy deals with highly heterogeneous, skewed, and bursty function workloads, and is a drop-in replacement for OpenWhisk's existing load-balancer. We leverage techniques from caching such as SHARDS for popularity detection, and develop a new approach that places functions based on a tradeoff between locality, load, and randomness.