How would you monitor the health of worker processes in a Node.js cluster in production?

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Accepted Answer

Monitoring worker health is critical in production to detect crashes, memory leaks, and unresponsive processes. There are multiple layers of monitoring: built-in Node.js cluster events for basic health, PM2 for process management dashboards, and APM (Application Performance Monitoring) tools for deep observability. const cluster = require('cluster');
const os = require('os');

if (cluster.isPrimary) {
  const workerHealth = {};

for (let i = 0; i < os.cpus().length; i++) {
    const worker = cluster.fork();
    workerHealth[worker.id] = { pid: worker.process.pid, lastHeartbeat: Date.now() };

worker.on('message', (msg) => {
      if (msg.type === 'HEARTBEAT') {
        workerHealth[worker.id].lastHeartbeat = Date.now();
      }
    });
  }

// Check heartbeats every 10 seconds
  setInterval(() => {
    const now = Date.now();
    Object.entries(workerHealth).forEach(([id, info]) => {
      if (now - info.lastHeartbeat > 15000) {
        console.warn(`Worker ${info.pid} unresponsive! Killing and restarting...`);
        cluster.workers[id]?.kill();
      }
    });
  }, 10000);

cluster.on('exit', (worker) => {
    delete workerHealth[worker.id];
    const newWorker = cluster.fork();
    workerHealth[newWorker.id] = { pid: newWorker.process.pid, lastHeartbeat: Date.now() };
  });

} else {
  // Worker sends heartbeat every 5 seconds
  setInterval(() => {
    process.send({ type: 'HEARTBEAT', pid: process.pid, memory: process.memoryUsage() });
  }, 5000);
} PM2 — pm2 monit provides real-time CPU/memory per worker, auto-restart on memory threshold breach Cluster lifecycle events — listen to online, exit, disconnect events on the cluster object Custom heartbeat via IPC — workers send periodic pings; master kills unresponsive ones after a timeout process.memoryUsage() — monitor heap usage per worker to detect memory leaks over time Datadog / New Relic APM — instrument workers with agents for distributed tracing and alerting Prometheus + Grafana — expose custom metrics per worker and aggregate via Prometheus scraping

How would you monitor the health of worker processes in a Node.js cluster in production?

Worker health in production is monitored using PM2's built-in monitoring dashboard, cluster lifecycle events (online, exit, disconnect), custom heartbeat mechanisms via IPC, and external APM tools like New Relic, Datadog, or Prometheus with Grafana.

How would you monitor the health of worker processes in a Node.js cluster in production?

Worker health in production is monitored using PM2's built-in monitoring dashboard, cluster lifecycle events (online, exit, disconnect), custom heartbeat mechanisms via IPC, and external APM tools like New Relic, Datadog, or Prometheus with Grafana.

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