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Node.JS
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This guide will show you how to get started with tracing in Node.js.

Example Application

This is a small example application we will monitor in this guide.

Dependencies

Install dependencies used by the example.

npm install express

Code

Please save the following code as app.js.

/* app.js */

const express = require("express");

const PORT = process.env.PORT || "8080";
const app = express();

app.get("/", (req, res) => {
  res.send("Hello World");
});

app.listen(parseInt(PORT, 10), () => {
  console.log(`Listening for requests on http://localhost:${PORT}`);
});

Run the application with the following request and open http://localhost:8080 in your web browser to ensure it is working.

$ node app.js
Listening for requests on http://localhost:8080

Tracing

Dependencies

The following dependencies are required to trace a Node.js application.

Core Dependencies

These dependencies are required to configure the tracing SDK and create spans.

  • @opentelemetry/api
  • @opentelemetry/node
  • @opentelemetry/tracing

Exporter

In the following example, we will use the ConsoleSpanExporter which prints all spans to the console.

In order to visualize and analyze your traces, you will need to export them to a tracing backend. Follow these instructions for setting up a backend and exporter.

You may also want to use the BatchSpanProcessor to export spans in batches in order to more efficiently use resources.

Instrumentation Modules

Many common modules such as the http standard library module, express, and others can be automatically instrumented using autoinstrumentation modules. To find autoinstrumenatation modules, you can look at the registry.

You can also install all instrumentations maintained by the OpenTelemetry authors by using the @opentelemetry/auto-instrumentations-node module.

Setup

The tracing setup and configuration should be run before your application code. One tool commonly used for this task is the -r, --require module flag.

Create a file with a name like tracing.js which will contain your tracing setup code.

/* tracing.js */

// Require dependencies
const { NodeTracerProvider } = require("@opentelemetry/node");
const { SimpleSpanProcessor, ConsoleSpanExporter } = require("@opentelemetry/tracing");
const { getNodeAutoInstrumentations } = require("@opentelemetry/auto-instrumentations-node');
const { registerInstrumentations } = require('@opentelemetry/instrumentation');

// Create a tracer provider
const provider = new NodeTracerProvider();

// The exporter handles sending spans to your tracing backend
const exporter = new ConsoleSpanExporter();

// The simple span processor sends spans to the exporter as soon as they are ended.
const processor = new SimpleSpanProcessor(exporter);
provider.addSpanProcessor(processor);

// The provider must be registered in order to
// be used by the OpenTelemetry API and instrumentations
provider.register();

// This will automatically enable all instrumentations
registerInstrumentations({
  instrumentations: [getNodeAutoInstrumentations()],
});

Run Application

First, install the dependencies as described above. Here you need to add the following:

npm install --save @opentelemetry/node @opentelemetry/auto-instrumentations-node

Now you can run your application as you normally would, but you can use the --require flag to load the tracing code before the application code.

$ node --require './tracing.js' app.js
Listening for requests on http://localhost:8080

Now, when you open http://localhost:8080 in your web browser, you should see the spans printed in the console by the ConsoleSpanExporter.

View example output 
{
  "traceId": "3f1fe6256ea46d19ec3ca97b3409ad6d",
  "parentId": "f0b7b340dd6e08a7",
  "name": "middleware - query",
  "id": "41a27f331c7bfed3",
  "kind": 0,
  "timestamp": 1624982589722992,
  "duration": 417,
  "attributes": {
    "http.route": "/",
    "express.name": "query",
    "express.type": "middleware"
  },
  "status": { "code": 0 },
  "events": []
}
{
  "traceId": "3f1fe6256ea46d19ec3ca97b3409ad6d",
  "parentId": "f0b7b340dd6e08a7",
  "name": "middleware - expressInit",
  "id": "e0ed537a699f652a",
  "kind": 0,
  "timestamp": 1624982589725778,
  "duration": 673,
  "attributes": {
    "http.route": "/",
    "express.name": "expressInit",
    "express.type": "middleware"
  },
  "status": { code: 0 },
  "events": []
}
{
  "traceId": "3f1fe6256ea46d19ec3ca97b3409ad6d",
  "parentId": "f0b7b340dd6e08a7",
  "name": "request handler - /",
  "id": "8614a81e1847b7ef",
  "kind": 0,
  "timestamp": 1624982589726941,
  "duration": 21,
  "attributes": {
    "http.route": "/",
    "express.name": "/",
    "express.type": "request_handler"
  },
  "status": { code: 0 },
  "events": []
}
{
  "traceId": "3f1fe6256ea46d19ec3ca97b3409ad6d",
  "parentId": undefined,
  "name": "GET /",
  "id": "f0b7b340dd6e08a7",
  "kind": 1,
  "timestamp": 1624982589720260,
  "duration": 11380,
  "attributes": {
    "http.url": "http://localhost:8080/",
    "http.host": "localhost:8080",
    "net.host.name": "localhost",
    "http.method": "GET",
    "http.route": "",
    "http.target": "/",
    "http.user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Safari/537.36",
    "http.flavor": "1.1",
    "net.transport": "ip_tcp",
    "net.host.ip": "::1",
    "net.host.port": 8080,
    "net.peer.ip": "::1",
    "net.peer.port": 61520,
    "http.status_code": 304,
    "http.status_text": "NOT MODIFIED"
  },
  "status": { "code": 1 },
  "events": []
}