Set up Prometheus: Install Prometheus, configure it to scrape metrics from a target service (e.g., a Node.js application), and verify that metrics are

Setting up Prometheus involves several steps, including installation, configuration, and verification. Here's a step-by-step guide to install Prometheus, configure it to scrape metrics from a Node.js application, and verify that the metrics are being collected.

Step 1: Install Prometheus

Download Prometheus: Go to the Prometheus download page and download the latest version for your operating system. For example, you can use wget or curl for Linux:
```
 wget https://github.com/prometheus/prometheus/releases/latest/download/prometheus-<version>.linux-amd64.tar.gz
```
Replace <version> with the latest version number.

Extract the downloaded file:

 tar xvf prometheus-<version>.linux-amd64.tar.gz
 cd prometheus-<version>.linux-amd64

Start Prometheus: You can start Prometheus with the default configuration by running:
```
 ./prometheus --config.file=prometheus.yml
```

Step 2: Set Up a Node.js Application with Metrics

Create a simple Node.js application:

If you don’t have a Node.js application, create a new one. Ensure you have Node.js and npm installed. Create a new directory and initialize a new project:
```
 mkdir node-app
 cd node-app
 npm init -y
```
Install the prom-client library:

This library helps expose metrics to Prometheus.
```
 npm install express prom-client
```

Create a simple Express server that exposes metrics:

Create a file named app.js with the following content:

 const express = require('express');
 const { register, collectDefaultMetrics } = require('prom-client');

 const app = express();
 const port = 3000;

 // Collect default metrics
 collectDefaultMetrics();

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

 // Expose the metrics endpoint
 app.get('/metrics', async (req, res) => {
     res.set('Content-Type', register.contentType);
     res.end(await register.metrics());
 });

 app.listen(port, () => {
     console.log(`Server running at http://localhost:${port}`);
 });

Start your Node.js application:
```
 node app.js
```

Step 3: Configure Prometheus to Scrape Metrics

Edit the prometheus.yml file:

Open the prometheus.yml file in the Prometheus directory and add a job configuration to scrape metrics from your Node.js application. It should look like this:
```
 global:
   scrape_interval: 15s  # Default scrape interval

 scrape_configs:
   - job_name: 'node-app'
     static_configs:
       - targets: ['localhost:3000']
```
This configuration tells Prometheus to scrape metrics from the Node.js application running on localhost at port 3000.
Restart Prometheus:

If Prometheus is still running, stop it (Ctrl + C) and start it again:
```
 ./prometheus --config.file=prometheus.yml
```

Step 4: Verify Metrics Collection

Access the Prometheus UI: Open your web browser and go to http://localhost:9090.
Check the targets: In the Prometheus UI, navigate to the “Status” -> “Targets” page. You should see your node-app listed there. It should show the last scrape time and any errors.
Query metrics: Navigate to the “Graph” page in the Prometheus UI. You can type in metrics like nodejs_http_requests_total or process_cpu_seconds_total to see if metrics are being collected.

Conclusion

You have now successfully set up Prometheus, configured it to scrape metrics from a Node.js application, and verified that metrics are being collected.