📋 3.12. Logging & Monitoring – Tracking Application Health

🤔 “Why is my app crashing?”
😫 “Where did that error come from?”
😵‍💫 “Is my app running slow for some users?”

These are questions every developer faces — even the pros.

That’s where logging and monitoring come in 💡.

It’s like giving your app a health checkup 🩺, so you can catch bugs, measure performance, and sleep peacefully at night 🛏️.

Let’s break it down in a fun, friendly way — like I’m teaching my little cousin!

🚀 What Is Logging & Monitoring?

📜 Logging

Logging is like writing a diary 📓 for your app.
It records what happens — good or bad.

Example:
“User logged in at 3:14 PM”
“Error: Database connection failed ❌”

🛰️ Monitoring

Monitoring is like checking your app’s heart rate in real-time ❤️‍🔥.
It tells you:

• How much memory your app is using
• If a process is stuck
• How many users are online

🎯 Why You Need It (Yes, You!)

Logging + Monitoring = A happy, healthy, maintainable app! 🎉

🛠️ Tools We’ll Use

We’ll use them together in a Node.js + Express setup.

🧱 Step-by-Step Logging with Morgan

1️⃣ Install Morgan

bashCopyEditnpm install morgan

2️⃣ Use It in Express App

jsCopyEditconst express = require('express');
const morgan = require('morgan');
const app = express();

app.use(morgan('tiny')); // or 'combined' for detailed logs

app.get('/', (req, res) => {
  res.send('Hello from Web Codder! 🎉');
});

app.listen(3000, () => console.log('Server running 🚀'));

Now every request (GET, POST, etc.) is logged like:

sqlCopyEditGET / 200 12ms - 150B

Super helpful for debugging slow routes or API misuse!

🧱 Structured Logging with Winston

1️⃣ Install Winston

bashCopyEditnpm install winston

2️⃣ Create a Logger File

jsCopyEdit// logger.js
const { createLogger, transports, format } = require('winston');

const logger = createLogger({
  level: 'info',
  format: format.combine(
    format.timestamp(),
    format.json() // logs as structured JSON
  ),
  transports: [
    new transports.Console(),
    new transports.File({ filename: 'logs/error.log', level: 'error' }),
    new transports.File({ filename: 'logs/combined.log' })
  ],
});

module.exports = logger;

3️⃣ Use Logger in App

jsCopyEditconst logger = require('./logger');

app.get('/test', (req, res) => {
  logger.info('Test route accessed ✅');
  res.send('Logging works!');
});

app.get('/fail', (req, res) => {
  logger.error('Something went wrong 😢');
  res.status(500).send('Error!');
});

Now your logs are organized by type and saved to files! 📁

🔢 Logging Levels Explained

Set different levels for dev and production 🔧.

📈 Real-Time Monitoring with PM2

1️⃣ Install PM2 Globally

bashCopyEditnpm install pm2 -g

2️⃣ Start Your App with PM2

bashCopyEditpm2 start app.js

Now PM2 keeps your app alive, even if it crashes!

3️⃣ View Logs & Status

bashCopyEditpm2 logs           // view live logs
pm2 list           // show all running apps
pm2 monit          // real-time dashboard 📊

4️⃣ Auto-Restart on Server Reboot

bashCopyEditpm2 startup
pm2 save

💡 Bonus: You can deploy multiple apps and scale them with PM2!

📊 Infographic (Insert Placeholder)

🧠 Pro Tips

• ✅ Use Morgan for quick request tracking
• ✅ Use Winston for deep debugging and file logs
• ✅ Use PM2 for real-time monitoring and zero-downtime restarts
• 🚫 Don’t log passwords or sensitive info!
• 🔐 Log only what you need in production to avoid bloated files

🔚 Conclusion: Keep Your App Healthy 🏥

Logging and monitoring are like having a doctor + bodyguard for your app.

They:

• Help you fix bugs faster 🐞
• Make your app more stable ⚙️
• Give you peace of mind at night 🌙

📣 Love Learning This Way?

Then you’ll love what’s coming next! 🧑‍💻

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Stay sharp, code smart, and track everything 🧠🚀