Workshop: Production Diagnostics for Node Applications

Node.js, the popular cross-platform JavaScript server framework, has grown in popularity and scale to the point where very challenging, non-trivial, production-only issues pop up in complex deployment environments. Although Node.js is equipped with the built-in V8 profiler, it is limited in scope to CPU time, which doesn’t account for the majority of Node.js performance issues. Also, profiling in production environments requires non-invasive tools with a low overhead, which do not require an application restart for the sake of profiling. In this workshop, we will learn, understand, and experiment with Node.js profiling tools designed for production use.

We will experiment with the built-in V8 profiler, and learn how to analyze its log output to zoom-in on CPU hot-spots in the V8 runtime, your JavaScript code, or external modules. We will also explore the Linux perf multi-tool, which can perform general-purpose CPU profiling, and how to get the Node.js runtime to generate symbolic information required to resolve stack traces emitted by perf. We will visualize stack traces using flame graphs, and understand where the CPU bottlenecks lie. We will also look at core dump analysis for crashes and memory leaks, and identify heap objects using the llnode plugin for lldb. In the second half of this workshop, we will talk about more complicated scenarios: diagnosing intermittent errors when connecting to a database or running queries, monitoring system I/O load, understanding the reasons for excessive V8 garbage collection, figuring out why your event loop thread is blocked, and more.

Outline:

• Node.js observability tools
• CPU profiling with V8
• Linux perf and CPU sampling
• Visualizing CPU profiles with flame graphs
• Introduction to BPF
• BPF scenarios and the BCC toolkit
• USDT probes
• Blocked-time analysis