multi-servers.js

// server.js
const express = require('express');
const httpProxy = require('http-proxy');
const axios = require('axios');

const app = express();
const proxy = httpProxy.createProxyServer({});

// Backends: must match ports from backend-cluster.js
const servers = [
  { url: 'http://localhost:5001', alive: true },
  { url: 'http://localhost:5002', alive: true },
  { url: 'http://localhost:5003', alive: true },
  { url: 'http://localhost:5004', alive: true },
  // Add more servers as needed
];

let current = -1; // start at -1 so first request -> index 0

function getNextServer() {
  const aliveServers = servers.filter(s => s.alive);
  if (!aliveServers.length) return null;
  current = (current + 1) % aliveServers.length;
  return aliveServers[current];
}

// proxy incoming requests
app.use((req, res) => {
  const target = getNextServer();
  if (!target) {
    return res.status(502).send('No backend servers are available.');
  }

  console.log(`→ Forwarding ${req.method} ${req.url} to ${target.url}`);

  proxy.web(req, res, { target: target.url }, (err) => {
    console.error(`Proxy error to ${target.url}:`, err.message);
    res.status(500).send('Proxy Error');
  });
});

// health checks: ping /health on each backend every 5s
async function checkServers() {
  await Promise.all(
    servers.map(async (server) => {
      try {
        await axios.get(server.url + '/health', { timeout: 1500 });
        if (!server.alive) console.log(`[HEALTH] ${server.url} is back UP`);
        server.alive = true;
      } catch {
        if (server.alive) console.log(`[HEALTH] ${server.url} is DOWN`);
        server.alive = false;
      }
    })
  );
}
setInterval(checkServers, 5000);
checkServers(); // do an initial check immediately

const PORT = 3000;
app.listen(PORT, () => console.log(`Reverse Proxy listening on port ${PORT}`));