FlowScope: Non-Intrusive Distributed Tracing with Method-Level Delay Estimation for Microservices Troubleshooting

As the scale and complexity of microservices increase, their operation and debugging become increasingly challenging. A single user request may involve interactions among hundreds of components. In such complex systems, non-intrusive distributed tracing techniques, which require no modification of application code, significantly enhance the convenience of troubleshooting. However, existing non-intrusive tracing frameworks still exhibit critical shortcomings in achieving tracing accuracy: current approaches either rely on specific thread model assumptions, limiting their applicability, or employ incorrectly constructed causal delay distributions to infer request causality, leading to erroneous trace construction. To overcome these limitations, we propose FlowScope, a non-intrusive distributed tracing framework for microservices that optimizes trace reconstruction through method-level delay distribution estimation. This framework estimates the causal delay distribution between requests of different method types via cross-correlation analysis, then uses these delay distributions to accurately evaluate the probability of causal relationships between requests. Subsequently, it efficiently reconstructs traces by incorporating multiple constraints with an iterative algorithm. Our testbed results indicate that FlowScope improves tracing accuracy by 51% compared to state-of-the-art frameworks (e.g., DeepFlow and TraceWeaver) and has been successfully applied in multiple real-world use cases.