How do I monitor event loop health in Node.js?
Use the built-in perf_hooks module to monitor event loop delay, APM tools like New Relic or Datadog for alerts, and clinic.js for diagnosis. Alert when event loop lag exceeds a threshold, and profile to find the blocking code.
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More FAQs in How to Monitor Event Loop Health in Node.js Production Apps
A measure of how far behind the event loop is. If it is consistently behind, something is blocking it with synchronous code. It is a key production metric, since it directly reflects how responsive your server is to requests.
Alert when event loop lag exceeds a threshold, like 100ms. This catches blocking operations early, before they affect many users. Use APM tools like Datadog or New Relic to track and alert on event loop lag automatically.
Profile with the CPU profiler to find the blocking code. The profiler shows which functions take the most time, which usually points directly at the synchronous code blocking the loop. Use clinic.js for visualization.
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