Setting Up Prometheus to Monitor a Node.js Application

Table of Contents

1. Introduction

2. Prerequisites

3. Installation Steps

   • Option 1: Manual Installation

   • Option 2: Docker Installation

4. Configuring Prometheus

5. Setting Up the Node.js Application for Metrics

6. Verifying Prometheus Scraping

7. Visualizing Metrics

8. Conclusion

---

Introduction

Prometheus is an open-source monitoring and alerting toolkit designed for reliability and scalability. It is especially well-suited for monitoring dynamic systems like microservices and applications built with Node.js. This documentation provides a step-by-step guide to setting up Prometheus for monitoring a Node.js application using the prom-client library to expose application metrics.

Prerequisites

Before starting the installation, ensure you have the following prerequisites in place:

• Operating System: A Linux or macOS machine.

• Node.js: A basic understanding of Node.js and Express (or another Node.js framework).

• Node.js Installed: Confirm Node.js is installed by running:

    node -v
  

• Docker (Optional): Basic understanding of Docker if you prefer to run Prometheus in a container.

Installation Steps

Option 1: Manual Installation

1. Download Prometheus: Fetch the latest version of Prometheus:

    wget https://github.com/prometheus/prometheus/releases/download/v2.46.0/prometheus-2.46.0.linux-amd64.tar.gz
   

2. Extract the Tarball: Unpack the downloaded file:

    tar -xvzf prometheus-2.46.0.linux-amd64.tar.gz
   

3. Navigate to the Directory: Change to the extracted Prometheus directory:

    cd prometheus-2.46.0.linux-amd64
   

4. Start Prometheus: Launch Prometheus with the default configuration:

    ./prometheus
   

   Prometheus will be accessible at http://localhost:9090.

Option 2: Docker Installation

If you prefer using Docker, follow these steps:

1. Run Prometheus in a Docker Container: Ensure to replace /path/to/prometheus.yml with the actual path to your Prometheus configuration file:

    docker run -d \
      --name prometheus \
      -p 9090:9090 \
      -v /path/to/prometheus.yml:/etc/prometheus/prometheus.yml \
      prom/prometheus
   

Configuring Prometheus

Prometheus requires a configuration file named prometheus.yml to define the services from which it should scrape metrics.

1. Create or Modify the prometheus.yml Configuration: Below is a sample configuration file that defines scraping for your Node.js application:

    global:
      scrape_interval: 15s  # Default scrape interval
   
    scrape_configs:
      - job_name: 'nodejs-app'  # Unique job name for the application
        static_configs:
          - targets: ['localhost:3000']  # Address of the Node.js application metrics endpoint
   

2. Save the Configuration and Restart Prometheus:

   • If running Prometheus manually:

       ./prometheus --config.file=prometheus.yml
     

   • If using Docker:

       docker restart prometheus
     

Setting Up the Node.js Application for Metrics

Prometheus collects metrics from a /metrics endpoint on your application. The prom-client library is used to expose these metrics.

1. Install the prom-client Library: In your Node.js project directory, install the library:

    npm install prom-client
   

2. Integrate Prometheus Metrics into Your Node.js Application: Below is an example of an Express.js application that exposes metrics:

    const express = require('express');
    const client = require('prom-client');
   
    const app = express();
    const port = 3000;
   
    // Create a Registry to register the metrics
    const register = new client.Registry();
   
    // Add default metrics to the registry
    client.collectDefaultMetrics({ register });
   
    // Custom metric - Counter
    const requestCounter = new client.Counter({
      name: 'http_requests_total',
      help: 'Total number of HTTP requests',
      labelNames: ['method', 'endpoint']
    });
   
    // Middleware to increment the counter on each request
    app.use((req, res, next) => {
      requestCounter.inc({ method: req.method, endpoint: req.url });
      next();
    });
   
    // Expose /metrics endpoint for Prometheus
    app.get('/metrics', async (req, res) => {
      res.set('Content-Type', register.contentType);
      res.end(await register.metrics());
    });
   
    // Start the application
    app.listen(port, () => {
      console.log(`Node.js app listening on http://localhost:${port}`);
    });
   

3. Run Your Node.js Application: Launch your application using:

    node app.js
   

   The application will now expose metrics at http://localhost:3000/metrics.

Verifying Prometheus Scraping

1. Access the Prometheus UI: Open your web browser and navigate to http://localhost:9090.

2. Check Scrape Targets: Go to Status > Targets to confirm that Prometheus is successfully scraping the Node.js application. Your nodejs-app target should be listed with a "UP" status.

Visualizing Metrics

Once Prometheus begins scraping metrics, you can use its powerful query language, PromQL, to visualize these metrics.

1. Navigate to the Graph Section of the Prometheus UI.

2. Enter Your Metric Query: In the query input box, type the name of a metric (e.g., http_requests_total).

3. Execute the Query and switch to the Graph tab to visualize the metric.

Conclusion

In this guide, we successfully set up Prometheus to monitor a Node.js application. We have:

• Installed Prometheus,

• Configured it to scrape metrics from a Node.js service,

• Integrated metrics collection within the Node.js application,

• Verified that metrics are being collected.

With Prometheus now configured, you can effectively monitor and analyze your Node.js application’s performance metrics. For enhanced visualization and dashboard capabilities, consider integrating Prometheus with Grafana.