npm package: @quickstat/rest
Description: Effortlessly monitor REST API metrics and export them to Prometheus for visualization in Grafana
Author: DxLoop
Latest version: 0.0.4

# REST Monitoring Plugin

The QuickStat REST Plugin offers seamless integration with REST instances, allowing effortless monitoring of key metrics. It exports these metrics to Prometheus, enabling visualization in Grafana dashboards.

If you are new to QuickStat and its component, feel free to check the [official documentation](https://www.npmjs.com/package/@quickstat/core) for a detailed breakdown.

![](https://raw.githubusercontent.com/QuickStat/quickstat/refs/heads/master/examples/plugins/rest/assets/rest_grafana_overview.png)
![](https://raw.githubusercontent.com/QuickStat/quickstat/refs/heads/master/examples/plugins/rest/assets/rest_grafana_distribution.png)

**If one of the following frameworks is being used, the dedicated plugins should be used instead of the REST plugin:**

- [Express.js Plugin](https://npmjs.com/package/@quickstat/expressjs)
- [Fastify Plugin](https://npmjs.com/package/@quickstat/fastify)
- [Koa Plugin](https://npmjs.com/package/@quickstat/koa)

## Installation

Start by installing the QuickStat core package, the data source used by grafana and then the REST plugin:

```bash
npm install @quickstat/core
npm install @quickstat/prometheus
npm install @quickstat/rest
```

## Getting Started

If you use docker and want to get started quickly, you can check the [following docker-setup](https://github.com/QuickStat/quickstat/tree/master/examples/plugins/rest), which allows you to skip the setup and directly use the plugin. Once you have setup docker, continue on Step 3.

If your unfamiliar with [QuickStat's plugins](https://github.com/QuickStat/quickstat/tree/master?tab=readme-ov-file#plugins), then keep in mind that you can also use other strategies such as (PushGateway) for exposing metrics or even combine your dashboard with other plugins.

If you want to set up Prometheus and Grafana manually, follow the steps below:

### 1. Setup Prometheus and Grafana

1. **Install Prometheus**: Follow the [official documentation](https://prometheus.io/docs/prometheus/latest/installation/) to install Prometheus on your system.

2. **Install Grafana**: Refer to the [official documentation](https://grafana.com/docs/grafana/latest/installation/) for instructions on installing Grafana.

3. **Configure Prometheus Data Source in Grafana**: After installing Grafana, configure Prometheus as a data source. Go to Grafana settings, add a new data source, and specify the URL where Prometheus is running.

### 2. Import Dashboard to Grafana

Once Prometheus and Grafana are set up, you can add [following Dashboard](https://grafana.com/grafana/dashboards/21152). Navigate to the Grafana dashboard page, click on "Import" and paste the dashboard template URL. Then, customize the dashboard as needed.

### 3. Expose REST Metrics

To expose the metrics to prometheus using the QuickStat REST Plugin, use the following code snippet:

```typescript
import { Client as QuickStatClient } from '@quickstat/core'
import { Pm2Plugin } from '@quickstat/pm2'
import { PrometheusDataSource, ScrapeStrategy } from '@quickstat/prometheus'
import pm2 from 'pm2' // uses the pm2 to get the metrics
import http from 'http'

// Create QuickStat Client
const quickStatClient = new QuickStatClient()<PrometheusDataSource<ScrapeStrategy>>({
  metrics: [],
  plugins: [
    // Register REST Plugin
    new RestPlugin(),
  ],
  // Register the data source
  dataSource: new PrometheusDataSource({
    strategy: new ScrapeStrategy(),
  }),
})

// [...] Observation logic

// Let Prometheus scrape the metrics at http://localhost:3242
// WARNING: On production, properly secure the endpoint (if open)
http.createServer(async (req, res) => {
  const response = await quickStatClient.dataSource?.strategy?.getResponse()

  // Write the prometheus response file
  if (response) {
    res.writeHead(200, response.headers)
    res.end(response.file)
  }
}).listen(3242)
```

### 4. Add Observation Logic

**If your REST framework is supported by the plugin, you should follow the framework guide for the plugin instead:**

- [Express Plugin](https://npmjs.com/package/@quickstat/expressjs)
- [Fastify Plugin](https://npmjs.com/package/@quickstat/fastify)
- [Koa Plugin](https://npmjs.com/package/@quickstat/koa)

Please refer to the respective documentation for more information.

If you want to observe the REST requests and the REST framework you are using does not has a dedicated plugin, you can use the `RestRequestObserver` to observe the requests. The following example shows how to observe a request in an express-like application:

```typescript
// [...]
app.get('/users/:id/todos', (req, res) => {
  const observer = new RestRequestObserver(quickStatClient) // Create a new request observer
  // [...] Your business logic
  observer.end(getObservationData(req, res)) // End the request observer and save observation data
})

// Function to get the observation data from the request
function getObservationData(req: Request, res: Response): ObserveRestRequestOptions {
  return {
    method: req.method as ObserveRestRequestOptions['method'],
    path: req.route.path, // get the path with variables
    status: res.statusCode,
    size: {
      request: req.socket.bytesRead,
      response: req.socket.bytesWritten,
    },
  }
}
```

### 5. Start the Application

After setting up the code, start the application. The metrics will be available at `http://localhost:3242` in Prometheus format and will be scraped by Prometheus, which will then be used for visualization in Grafana.

## Configuration

### DataSource

The example above uses the PrometheusDataSource with the ScrapeStrategy. The ScrapeStrategy exposes the prometheus file on the given endpoint for being scraped from prometheus. You can also use the PushGatewayStrategy to push the metrics to the PushGateway of Prometheus.

If you would like to use other data sources, you can take a look at the available data sources in the [@quickstat/core](https://github.com/QuickStat/quickstat?tab=readme-ov-file#data-sources) package.

### Plugin

| Option         | Description                 | Default |
| -------------- | --------------------------- | ------- |
| excludeMetrics | Array of metrics to exclude | []      |

## Contributing and Issues

If you have any issues or feature requests, feel free to open an issue on the [GitHub repository](https://github.com/QuickStat/quickstat)