Q54- How would you monitor and log your Node.js application in production?

Monitoring and logging are essential for production applications to detect errors, track performance, and ensure reliability.

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🔹 1. Logging

Purpose: Track events, errors, and important actions in your app.

Common Tools:

• Winston – flexible logging library with multiple transports (console, file, remote).
• Morgan – HTTP request logging for Express.js.
• Bunyan – JSON-based structured logging for easy parsing.

Example with Winston:

const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  transports: [
    new winston.transports.File({ filename: 'error.log', level: 'error' }),
    new winston.transports.File({ filename: 'combined.log' }),
  ],
});

logger.info('Server started');
logger.error('Something went wrong');

Example with Morgan in Express:

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

app.use(morgan('combined')); // Logs HTTP requests

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🔹 2. Monitoring

Purpose: Observe app health, performance, and resource usage.

Approaches:

1. Application Performance Monitoring (APM):
   • Tools: New Relic, Datadog, AppDynamics, Elastic APM
   • Monitor response times, throughput, error rates, CPU/memory usage.
2. Process Monitoring:
   • Tools: PM2, Forever
   • Keep Node.js processes alive, monitor CPU/memory, enable automatic restarts.

# Start app with PM2 and enable monitoring
pm2 start server.js --name my-app
pm2 monit

1. Custom Metrics:
   • Use libraries like prom-client for Prometheus metrics: request counts, response times, memory usage.
   • Expose metrics endpoint and integrate with Grafana for visualization.

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🔹 3. Error Tracking

• Capture unhandled errors and rejections:

process.on('uncaughtException', (err) => {
  logger.error('Uncaught Exception:', err);
});

process.on('unhandledRejection', (reason) => {
  logger.error('Unhandled Rejection:', reason);
});

• Integrate with Sentry or LogRocket for real-time error tracking.

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🔹 4. Key Best Practices

• Log structured JSON for easier parsing and aggregation.
• Separate error logs and info logs.
• Rotate logs to avoid disk full issues (winston-daily-rotate-file).
• Monitor CPU, memory, response times, DB latency, and API errors.
• Set up alerts for critical thresholds.

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✅ Summary:

• Use Winston/Morgan for logging, PM2/APM tools for monitoring.
• Capture uncaught exceptions and unhandled promise rejections.
• Visualize metrics and set up alerts to maintain production health.