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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.

npm install @opentelemetry/sdk-node @opentelemetry/api

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.

npm install @opentelemetry/auto-instrumentations-node

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 opentelemetry = require("@opentelemetry/sdk-node");
const { getNodeAutoInstrumentations } = require("@opentelemetry/auto-instrumentations-node");

const sdk = new opentelemetry.NodeSDK({
  traceExporter: new opentelemetry.tracing.ConsoleSpanExporter(),
  instrumentations: [getNodeAutoInstrumentations()]
});

sdk.start()

Run Application

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

Open http://localhost:8080 in your web browser and reload the page a few times, after a while 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": []
}

Metrics

Dependencies

The following dependencies are required to collect metrics in your Node.js application.

Core Dependencies

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

  • @opentelemetry/metrics

Exporter

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

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

Setup

You need a Meter to create and monitor metrics. A Meter in OpenTelemetry is the mechanism used to create and manage metrics, labels, and metric exporters.

Create a file named monitoring.js and add the following code:

/* monitoring.js */
'use strict';

const { MeterProvider, ConsoleMetricExporter } = require('@opentelemetry/metrics');

const meter = new MeterProvider({
  new ConsoleMetricExporter(),
  interval: 1000,
}).getMeter('your-meter-name');

Now you can require this file from your application code and use the Meter to create and manage metrics. The simplest of these metrics is a counter.

Let's create and export from your monitoring.js file a middleware function that express can use to count all requests by route. Modify the monitoring.js file so it looks like this:

/* monitoring.js */
'use strict';

const { MeterProvider, ConsoleMetricExporter } = require('@opentelemetry/metrics');

const meter = new MeterProvider({
  new ConsoleMetricExporter(),
  interval: 1000,
}).getMeter('your-meter-name');

const requestCount = meter.createCounter("requests", {
  description: "Count all incoming requests"
});

const boundInstruments = new Map();

module.exports.countAllRequests = () => {
  return (req, res, next) => {
    if (!boundInstruments.has(req.path)) {
      const labels = { route: req.path };
      const boundCounter = requestCount.bind(labels);
      boundInstruments.set(req.path, boundCounter);
    }

    boundInstruments.get(req.path).add(1);
    next();
  };
};

Now import and use this middleware in your application code app.js:

/* app.js */
const express = require("express");
const { countAllRequests } = require("./monitoring");
const app = express();
app.use(countAllRequests());
/* ... */

Now when you make requests to your service, your meter will count all requests.

Note: Creating a new labelSet and binding on every request is not ideal because creating the labelSet can often be an expensive operation. Therefore, the instruments are created and stored in a Map according to the route key.

Run Application

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

npm install --save @opentelemetry/metrics

Now you can run your application:

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

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

{
  "name": "requests",
  "description": "Count all incoming requests",
  "unit": "1",
  "metricKind": 0,
  "valueType": 1
}
{ "route": "/" }
"value": "1"