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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Importing and initializing the OpenTelemetry SDK as a regular import inside the main application file

// Wrong: SDK starts too late, after Express is already imported
import express from "express";
import { sdk } from "./tracing.js";
sdk.start();

// Correct: node --require ./tracing.js server.js
// tracing.js runs and patches libraries BEFORE server.js imports them

The Solution //

Auto-instrumentation works by patching library internals (like Express or the HTTP module) at the moment they're first imported — if the SDK initializes after those libraries are already imported elsewhere in the module graph, the patching never applies and no spans are generated. The SDK must be loaded via --require (or an equivalent preload mechanism) before any other application code runs.

The Error //

Assuming OpenTelemetry auto-instrumentation captures custom business logic automatically

// Not automatically traced — pure business logic
function calculatePricing(order) { /* ... */ }

// Requires an explicit manual span for visibility
const span = tracer.startSpan("calculatePricing");
try { return calculatePricing(order); } finally { span.end(); }

The Solution //

Auto-instrumentation only creates spans for supported libraries it knows how to patch — HTTP calls, common database drivers, popular frameworks. Custom business logic (like a complex pricing calculation) is invisible to auto-instrumentation entirely and requires an explicit manual span to be traced.