Monitoring your Express application using OpenTelemetry

October 18, 2023 · 7 min read

SigNoz Team

Nodejs is a popular Javascript runtime environment that executes Javascript code outside of a web browser. Express is the most popular web frameworks that sits on top of Nodejs and adds functionalities like middleware, routing, etc. to Nodejs.

Cover Image

You can monitor your express application using OpenTelemetry and a tracing backend of your choice. OpenTelemetry is the leading open-source standard under the Cloud Native Computing Foundation that aims to standardize the process of instrumentation across multiple languages.

In this article, we will be using SigNoz to store and visualize the telemetry data collected by OpenTelemetry from a sample Expressjs application.

Running an Express application with OpenTelemetry

OpenTelemetry is a set of tools, APIs, and SDKs used to instrument applications to create and manage telemetry data(logs, metrics, and traces).

Install SigNoz

You can get started with SigNoz using just three commands at your terminal.

git clone -b main https://github.com/SigNoz/signoz.git
cd signoz/deploy/
./install.sh

For detailed instructions, you can visit our documentation.

When you are done installing SigNoz, you can access the UI at: http://localhost:3301

The application list shown in the dashboard is from a sample app called HOT R.O.D that comes bundled with the SigNoz installation package.

SigNoz dashboard home — *List of applications shown as an example on SigNoz dashboard*

Creating a sample express application

You need to ensure that you have Node.js version 12 or newer. You can download the latest version of Node.js here. For the sample application, let's create a basic 'hello world' express.js application.

If you do not want to follow these steps manually, you can directly check out the GitHub repo of the sample application. You can run the app directly after cloning it and start sending data to SigNoz. The code is already instrumented with OpenTelemetry libraries.

But, it would be better if you follow these steps to understand what's happening.

Check if node is installed on your machine by using the below command:

node - v;

Steps to get the app set up and running:

Make a directory and install express
Make a directory for your sample app on your machine. Then open up the terminal, navigate to the directory path and install express with the following command:
```
npm i express
```

Create index.js
Create a file called index.js in your directory and with any text editor setup your 'Hello World' file with the code below:

const express = require("express");
const cors = require("cors");
const PORT = process.env.PORT || "5555";
const app = express();

app.use(cors());
app.use(express.json());

app.all("/", (req, res) => {
  res.json({ method: req.method, message: "Hello World", ...req.body });
});

app.get("/404", (req, res) => {
  res.sendStatus(404);
});

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

Check if your application is working
Run your application by using the below command at your terminal.
```
node index.js
```
You can check if your app is working by visiting: http://localhost:5555/
Once you are finished checking, exit the application by using Ctrl + C on your terminal.

Set up OpenTelemetry and send data to SigNoz

Install OpenTelemetry packages
You will need the following OpenTelemetry packages for this sample application.
```
npm install --save @opentelemetry/sdk-node
npm install --save @opentelemetry/auto-instrumentations-node
npm install --save @opentelemetry/exporter-trace-otlp-http
```
The dependencies included are briefly explained below:
@opentelemetry/sdk-node - This package provides the full OpenTelemetry SDK for Node.js including tracing and metrics.
@opentelemetry/auto-instrumentations-node - This module provides a simple way to initialize multiple Node instrumentations.
@opentelemetry/exporter-trace-otlp-http - This module provides the exporter to be used with OTLP (http/json) compatible receivers.
note
If you run into any error, you might want to use these pinned versions of OpenTelemetry libraries used in this GitHub repo.

Create tracing.js file
Instantiate tracing by creating a tracing.js file and using the below code.

// tracing.js
"use strict";
const process = require("process");
const opentelemetry = require("@opentelemetry/sdk-node");
const {
  getNodeAutoInstrumentations,
} = require("@opentelemetry/auto-instrumentations-node");
const {
  OTLPTraceExporter,
} = require("@opentelemetry/exporter-trace-otlp-http");
const { Resource } = require("@opentelemetry/resources");
const {
  SemanticResourceAttributes,
} = require("@opentelemetry/semantic-conventions");

const exporterOptions = {
  url: "http://localhost:4318/v1/traces",
};

const traceExporter = new OTLPTraceExporter(exporterOptions);
const sdk = new opentelemetry.NodeSDK({
  traceExporter,
  instrumentations: [getNodeAutoInstrumentations()],
  resource: new Resource({
    [SemanticResourceAttributes.SERVICE_NAME]: "node_app",
  }),
});

// initialize the SDK and register with the OpenTelemetry API
// this enables the API to record telemetry

sdk.start();

// gracefully shut down the SDK on process exit
process.on("SIGTERM", () => {
  sdk
    .shutdown()
    .then(() => console.log("Tracing terminated"))
    .catch((error) => console.log("Error terminating tracing", error))
    .finally(() => process.exit(0));
});

OpenTelemetry Node SDK currently does not detect the OTEL_RESOURCE_ATTRIBUTES from .env files as of today. That’s why we need to include the variables in the tracing.js file itself.

About environment variables:

service_name: name of the service you want to monitor

environment: dev, prod, staging, etc.

http://localhost:4318/v1/traces is the default url for sending your tracing data. We are assuming you have installed SigNoz on your localhost. Based on your environment, you can update it accordingly. It should be in the following format:

http://<IP of SigNoz backend>:4318/v1/traces

note

Remember to allow incoming requests to port 4318 of machine where SigNoz backend is hosted.

Run your application
Now when you run your application, OpenTelemetry captures telemetry data from it and send it to SigNoz.
```
node -r ./tracing.js index.js
```
You can check your application running at http://localhost:5555/. You need to generate some load in order to see data reported on SigNoz dashboard. Refresh the endpoint for 10-20 times, and wait for 2-3 mins.

And, congratulations! You have instrumented your sample Node.js app. You can now access the SigNoz dashboard at http://localhost:3301 to monitor your app for performance metrics.

*Express app in the list of applications*

SigNoz is open-source, and a full-stack APM. It comes with charts of RED metrics and a seamless transition from metrics to traces.

Open-source tool to visualize telemetry data

SigNoz makes it easy to visualize metrics and traces captured through OpenTelemetry instrumentation.

SigNoz comes with out of box RED metrics charts and visualization. RED metrics stands for:

Rate of requests
Error rate of requests
Duration taken by requests

SigNoz charts and metrics — *Measure things like application latency, requests per sec, error percentage and see your top endpoints with SigNoz.*

You can then choose a particular timestamp where latency is high to drill down to traces around that timestamp.

List of traces on SigNoz dashboard — *View of traces at a particular timestamp*

You can use flamegraphs to exactly identify the issue causing the latency.

Flamegraphs used to visualize spans of distributed tracing in SigNoz UI — *View of traces at a particular timestamp*

You can also build custom metrics dashboard for your infrastructure.

Conclusion

OpenTelemetry makes it very convenient to instrument your Express application. You can then use an open-source APM tool like SigNoz to analyze the performance of your app. As SigNoz offers a full-stack observability tool, you don't have to use multiple tools for your monitoring needs.

You can try out SigNoz by visiting its GitHub repo 👇