Fine-grained Tracing for Performance Anomaly Diagnosis of Serverless Functions

Serverless function compositions subject to unpredictable faults are challenging to evaluate for root cause analysis. Even though distributed tracing provides observations at multiple levels of granularity for troubleshooting, excessive code instrumentation increases the tracing overheads in terms of both computation and storage. Therefore, developers face the challenge of where and how to instrument serverless functions to maximize the likelihood of locating faults based on tracing data while minimizing tracing overhead and costs. In this article, we propose a methodology to instrument an application with code-level tracing to infer the location of faults, taking into account constraints in terms of the maximum cost of the instrumentation and testing. We encode the tracing probe placement based on the control flow graph of the application and devise heuristics-based tracing data collection strategies to relate possible probe placements with their ability to locate a fault. Then we train novelty detection models to identify the internal anomalies and present an enhanced global search algorithm that automatically computes a probe placement with optimal fault localization ability versus cost. Experimental results show high performance in locating single and multiple faults with over 90% recall score for up to 15% latency anomalies, with minimal instrumentation overhead.