Analyzing Tail Latency in Serverless Clouds with STeLLAR

Serverless computing has seen rapid adoption because of its instant scalability, flexible billing model, and economies of scale. In serverless, developers structure their applications as a collection of functions invoked by various events like clicks, and cloud providers take responsibility for cloud infrastructure management. As with other cloud services, serverless deployments require responsiveness and performance predictability manifested through low average and tail latencies. While the average end-to-end latency has been extensively studied in prior works, existing papers lack a detailed characterization of the effects of tail latency in real-world serverless scenarios and their root causes. In response, we introduce STeLLAR, an open-source serverless benchmarking framework, which enables an accurate performance characterization of serverless deployments. STeLLAR is provider-agnostic and highly configurable, allowing the analysis of both end-to-end and per-component performance with minimal instrumentation effort. Using STeLLAR, we study three leading serverless clouds and reveal that storage accesses and bursty function invocation traffic are key factors impacting tail latency in modern serverless systems. Finally, we identify important factors that do not contribute to latency variability, such as the choice of language runtime.