Monitoring Bun Apps

📡 Introduction to Monitoring Bun Apps

Your Bun app is fast. Really fast. ⚡ But speed alone isn't enough. In production, what truly matters is visibility — knowing when your app breaks, slows down, or behaves unexpectedly. That's where monitoring comes in.

Monitoring allows you to track performance, uptime, errors, and logs. In this guide, we'll explore how to effectively monitor Bun applications using both built-in tools and external services.

🧐 Why Monitoring Is Crucial

Let’s break it down — why monitor at all?

• Detect crashes before users report them
• Catch slow API responses early
• Understand usage patterns (e.g., traffic spikes)
• Audit errors and logs during debugging

Even a minor bug in your Bun backend could hurt conversions or reputation. Proactive monitoring keeps you ahead of issues.

📊 Basic Metrics to Track

Here are the key performance indicators (KPIs) to watch for your Bun app:

• Request count per second
• Error rate (e.g., 500s, 404s)
• Response time (avg, p95)
• CPU and memory usage

⚙️ Setting Up Custom Logging

Start with custom logs right inside your Bun server. Here’s an enhanced logger to track requests and performance:

const server = Bun.serve({
  port: 3000,
  async fetch(req) {
    const start = Date.now();
    const res = new Response("Hello from Bun 🚀");
    const duration = Date.now() - start;

    console.log(`[${new Date().toISOString()}] ${req.method} ${req.url} - ${duration}ms`);
    return res;
  }
});

These logs will help you spot slow endpoints and understand traffic patterns instantly.

💥 Logging Errors and Exceptions

If your app throws an error, you should log it clearly. Wrap risky code in try/catch and send useful logs:

try {
  // risky operation
  throw new Error("Something broke!");
} catch (err) {
  console.error("❌ Error caught:", err.message);
}

You can even log stack traces to debug faster during production incidents.

📬 Sending Logs to External Services

Want centralized logs? Pipe logs to services like:

• Logtail or Datadog (via HTTP API)
• Loki (Grafana) for time-series logs
• Sentry for error monitoring

// Example: send logs to Logtail
await fetch("https://in.logtail.com", {
  method: "POST",
  headers: {
    Authorization: "Bearer YOUR_API_KEY",
    "Content-Type": "application/json"
  },
  body: JSON.stringify({ message: "API /home accessed", level: "info" })
});

This gives you a centralized dashboard to inspect logs without SSHing into servers.

📈 Prometheus + Grafana for Metrics

If you want charts and dashboards, Prometheus is your friend. Expose a metrics endpoint like this:

const metrics = {
  requestCount: 0,
  errorCount: 0
};

const server = Bun.serve({
  port: 3000,
  fetch(req) {
    if (req.url.endsWith("/metrics")) {
      return new Response(
        `# HELP request_count Number of requests\nrequest_count ${metrics.requestCount}`
      );
    }

    metrics.requestCount++;
    return new Response("Hello from Bun");
  }
});

You can then scrape this with Prometheus and display it on a Grafana dashboard.

🧠 Health Checks & Uptime Monitoring

Create a dedicated /health endpoint to confirm your app is live:

if (req.url.endsWith("/health")) {
  return new Response(JSON.stringify({ status: "ok", uptime: process.uptime() }), {
    headers: { "Content-Type": "application/json" }
  });
}

Use uptime monitoring tools like UptimeRobot or BetterStack to ping this route every 30–60 seconds.

🧪 Real-time Monitoring with Bun + WebSockets

Want to get fancy? Create a WebSocket connection to stream logs to your terminal or UI dashboard.

const server = Bun.serve({
  websocket: {
    open(ws) {
      ws.send("🔍 Live log stream started...");
    },
    message(ws, msg) {
      console.log("Log:", msg);
    }
  },
  port: 3000
});

With WebSockets, you can visualize metrics in real time on a custom dashboard.

🧰 Bonus Tools to Try

• PM2 ➝ Process manager with built-in logging & monitoring
• SigNoz ➝ Open-source APM for performance insights
• OpenTelemetry ➝ Unified telemetry standard (can be integrated with Bun)

🏁 Wrapping Up: Stay Ahead of Failures

Monitoring your Bun app ensures you're not flying blind in production. Whether it's error logs, health checks, or detailed metrics, visibility = stability.

Start simple with Bun’s native logging, and grow into more advanced monitoring as your app scales. The key is: don’t wait for issues to hit users — catch them before they spread 🧯.