Here's your updated README based on the provided code changes:

Performance Radiator

performance-radiator is a Node.js package for monitoring and exposing critical application performance metrics. Built using Prometheus's prom-client, it offers a flexible solution for developers to track application health, manage rate limits, and customize metrics as needed.

Features

• Core Metrics: Tracks essential performance indicators such as HTTP requests, errors, concurrent users, and rate-limited requests.
• Dynamic Metrics: Allows developers to add counters, gauges, and histograms at runtime.
• Rate Limiting: Includes configurable rate-limiting middleware to manage incoming traffic.
• Prometheus Integration: Exposes metrics in a Prometheus-compatible format.
• Easy Integration: Quickly set up and monitor your Express-based applications.

Installation

npm install performance-radiator

Usage

Initialization

1. Set Up Middleware
   Integrate performance-radiator into your Express app:

   const express = require("express");
   const createPerformanceMonitor = require("performance-radiator");
   
   const app = express();
   
   const {
     router: metricsRouter,
     applyRateLimiter,
     httpRequestsTotal,
   } = createPerformanceMonitor({
     sequelize: require("./models").sequelize, // Optional Sequelize integration
     rateLimitOptions: { windowMs: 60000, max: 100 }, // Rate limit config
     customMetrics: [
       {
         type: "counter",
         name: "custom_event_count",
         help: "Custom metric example",
       },
     ],
   });
   
   // Apply rate limiter globally or to specific routes
   applyRateLimiter(app, "/");
   
   // Attach metrics endpoint
   app.use("/metrics", metricsRouter);
   
   app.listen(3000, () => console.log("Server running on port 3000"));

Adding Custom Metrics

Add metrics dynamically via the customMetrics option or programmatically.

const { httpRequestsTotal } = require("performance-radiator");

// Add a custom counter metric
httpRequestsTotal.inc({ method: "GET", route: "/", status: 200 });

Built-In Metrics

The package provides these default metrics:

HTTP Metrics

• http_requests_total: Total HTTP requests (labels: method, route, status).
• http_errors_total: Total HTTP errors (labels: method, route).
• http_request_throughput: Current request throughput.
• http_rate_limit_total: Requests blocked by rate limiter (labels: route).

User Metrics

• http_concurrent_users: Number of concurrent users.

Database Metrics (via Sequelize, if configured)

• Metrics for query durations, active connections, and transactions.

Rate Limiting

Use rateLimitOptions to configure rate limits.

applyRateLimiter(app, "/api", { windowMs: 60000, max: 50 });

Default options:

• windowMs: Time window in milliseconds.
• max: Max requests per window.

Prometheus Integration

Expose the /metrics endpoint for Prometheus to scrape metrics. Add this configuration to Prometheus:

scrape_configs:
  - job_name: 'my_app'
    static_configs:
      - targets: ['localhost:3000']

Full Example

const express = require("express");
const createPerformanceMonitor = require("performance-radiator");
const sequelize = require("./models").sequelize;

const app = express();

const { router: metricsRouter, applyRateLimiter } = createPerformanceMonitor({
  sequelize,
  rateLimitOptions: { windowMs: 60000, max: 100 },
  customMetrics: [
    {
      type: "gauge",
      name: "active_sessions",
      help: "Tracks active user sessions",
    },
  ],
});

applyRateLimiter(app);
app.use("/metrics", metricsRouter);

app.get("/", (req, res) => {
  res.send("Welcome to Performance Radiator!");
});

app.listen(3000, () => console.log("Server running on port 3000"));

License

This project is licensed under the MIT License.

This updated README includes key changes in functionality and maintains clarity for users integrating performance-radiator.