How to Monitor Petit-dom with Vigilmon

Petit-dom is a minimalist virtual DOM library optimized for minimal bundle size and high-performance diffing — it provides a lean, expressive API for building reactive UIs without the weight of larger frameworks. It's a natural fit for performance-critical apps and embedded widgets where every kilobyte matters. But a tiny virtual DOM can't protect you from a crashed backend, a failed deploy, or a silently broken data feed. Vigilmon provides continuous HTTP monitoring, heartbeat checks, and instant alerts so you know the moment something breaks — before your users do.

What You'll Build

• A /health endpoint for your Petit-dom Node.js backend
• Vigilmon HTTP monitors for your app and API
• A heartbeat monitor for background jobs
• Alert channels (email and Slack)
• An uptime badge rendered in your Petit-dom UI

Prerequisites

• A Node.js project using Petit-dom (with Express or a plain HTTP server)
• A free Vigilmon account

Step 1: Add a Health Endpoint

Petit-dom handles client-side virtual DOM updates, but your server needs an HTTP health endpoint that Vigilmon can poll at regular intervals:

// server.js
import express from "express";

const app = express();

app.get("/health", async (req, res) => {
  const checks = {};
  let degraded = false;

  // Database connectivity check
  try {
    // await db.query("SELECT 1");
    checks.database = "ok";
  } catch (err) {
    checks.database = `error: ${err.message}`;
    degraded = true;
  }

  // Cache check (e.g. Redis)
  try {
    // await redisClient.ping();
    checks.cache = "ok";
  } catch (err) {
    checks.cache = `error: ${err.message}`;
    degraded = true;
  }

  res.status(degraded ? 503 : 200).json({
    status: degraded ? "degraded" : "ok",
    timestamp: new Date().toISOString(),
    checks,
  });
});

// Serve your Petit-dom app's static assets
app.use(express.static("public"));

app.listen(process.env.PORT ?? 3000, () => {
  console.log("Server running on port", process.env.PORT ?? 3000);
});

Test it locally:

curl http://localhost:3000/health | jq .
# {"status":"ok","timestamp":"2026-07-03T...","checks":{"database":"ok","cache":"ok"}}

Step 2: Configure Vigilmon HTTP Monitors

Log in to Vigilmon → Monitors → New Monitor:

Monitor 1: Petit-dom App (Frontend)

| Field | Value | |---|---| | URL | https://yourapp.com/ | | Method | GET | | Expected status | 200 | | Expected body | A stable string from your HTML shell | | Check interval | 1 minute |

Monitor 2: Health API

| Field | Value | |---|---| | URL | https://yourapp.com/health | | Method | GET | | Expected status | 200 | | Expected body | "status":"ok" | | Check interval | 1 minute |

Two independent monitors keep failure classes separate: a CDN outage (frontend down, API healthy) is distinct from a database failure (API degraded, frontend still cached).

Step 3: Heartbeat for Background Tasks

Petit-dom UIs often render data produced by background jobs — scheduled data fetches, cache refresh tasks, or aggregation pipelines. A Vigilmon heartbeat monitor detects when these jobs stop running silently:

// scheduler.js
import cron from "node-cron";

const VIGILMON_HEARTBEAT_URL = process.env.VIGILMON_HEARTBEAT_URL ?? "";

async function pingHeartbeat() {
  if (!VIGILMON_HEARTBEAT_URL) return;
  try {
    await fetch(VIGILMON_HEARTBEAT_URL, { signal: AbortSignal.timeout(5000) });
  } catch {
    // Never let heartbeat errors crash the scheduler
  }
}

// Run every 5 minutes for a real-time data pipeline
cron.schedule("*/5 * * * *", async () => {
  try {
    await refreshDataCache();
    await pingHeartbeat(); // Only ping after successful execution
  } catch (err) {
    console.error("[scheduler] Data refresh failed:", err);
    // No ping → Vigilmon alerts when the heartbeat window expires
  }
});

async function refreshDataCache() {
  // Pull fresh data for your Petit-dom views
}

Set up the heartbeat in Vigilmon:

1. Monitors → New Heartbeat Monitor
2. Set Expected interval to 10 minutes (2× the cron interval)
3. Add the ping URL to your environment:

VIGILMON_HEARTBEAT_URL=https://vigilmon.online/api/heartbeat/xxxxxxxx

Step 4: Embed an Uptime Badge in Your Petit-dom UI

Petit-dom uses a hyperscript-style h function to build virtual nodes. You can include a Vigilmon status badge as a static vnode in your component tree:

// app.js (client-side with Petit-dom)
import h from "petit-dom";

const BADGE_URL = "https://vigilmon.online/api/badge/your-monitor-id.svg";
const STATUS_URL = "https://vigilmon.online/status/your-monitor-slug";

function App(data) {
  return h("div", { class: "app" },
    h("main", null, Content(data)),
    h("footer", { class: "footer" },
      h("a", {
        href: STATUS_URL,
        target: "_blank",
        rel: "noopener noreferrer",
        "aria-label": "Service uptime status",
      },
        h("img", {
          src: BADGE_URL,
          alt: "Uptime",
          width: 120,
          height: 20,
        })
      )
    )
  );
}

function Content(data) {
  return h("p", null, data.message);
}

// Initial render
import { patch } from "petit-dom";
const container = document.getElementById("app");
let tree = App({ message: "Your content here." });
patch(container, tree);

// Update on data change
function update(data) {
  const newTree = App(data);
  patch(tree, newTree);
  tree = newTree;
}

Petit-dom's efficient structural diffing means the static badge image node is never patched unless its attributes change — ideal for a status indicator that updates independently via the Vigilmon CDN.

Step 5: Set Up Alert Channels

In Vigilmon's Alert Channels settings:

Email Alerts

1. Alert Channels → Email → add your on-call address
2. Attach the channel to both HTTP monitors and the heartbeat monitor

Slack Alerts

1. Create a Slack Incoming Webhook for your #alerts channel
2. Alert Channels → Webhook → paste the Slack webhook URL
3. Use this payload template:

{
  "text": "🚨 *{{ monitor.name }}* is DOWN\n{{ monitor.url }}\nStatus: {{ event.status }}\n<https://vigilmon.online|Open Vigilmon>"
}

Step 6: Verify Everything Works

# 1. Confirm health endpoint returns 200
curl -s https://yourapp.com/health | jq .status

# 2. Simulate a failure — break your DB connection string and redeploy
# Expected: health endpoint returns 503; Vigilmon alerts within ~2 minutes

# 3. Remove the heartbeat URL and let the scheduler run one cycle
# Expected: heartbeat alert fires after the grace window expires

# 4. In Vigilmon → "Test Alert" to confirm Slack/email delivery

Summary

| Monitor | What It Catches | |---|---| | HTTP app check | CDN failures, broken static file serving | | HTTP health API | Database, cache, and external dependency failures | | Heartbeat | Scheduler crashes, silent data refresh failures |

Next Steps

• Create separate Vigilmon projects for staging and production
• Use Vigilmon's response time graphs to detect backend latency regressions alongside Petit-dom's render timing
• Configure escalating alerts: email for recoveries, Slack for active outages, PagerDuty for SLA-critical monitors

Ready to get started? Sign up for Vigilmon free — have your first monitor running in under 5 minutes.