monitoring-logging

Monitoring & Logging

Overview

Application observability through logging, metrics collection, monitoring dashboards, and alerting systems.

Structured Logging

Pino Logger (Node.js)

import pino from 'pino';

// Base logger configuration
const logger = pino({
  level: process.env.LOG_LEVEL || 'info',
  formatters: {
    level: (label) => ({ level: label }),
    bindings: () => ({}), // Remove pid and hostname
  },
  timestamp: pino.stdTimeFunctions.isoTime,
  redact: {
    paths: ['password', 'token', 'authorization', '*.password', '*.token'],
    censor: '[REDACTED]',
  },
});

// Child logger with context
function createRequestLogger(req: Request) {
  return logger.child({
    requestId: req.headers['x-request-id'] || crypto.randomUUID(),
    method: req.method,
    path: req.path,
    userAgent: req.headers['user-agent'],
    userId: req.user?.id,
  });
}

// Express middleware
app.use((req, res, next) => {
  req.log = createRequestLogger(req);

  const startTime = Date.now();

  res.on('finish', () => {
    const duration = Date.now() - startTime;

    req.log.info({
      statusCode: res.statusCode,
      duration,
      contentLength: res.get('content-length'),
    }, 'request completed');
  });

  next();
});

// Usage in handlers
app.get('/api/users/:id', async (req, res) => {
  req.log.info({ userId: req.params.id }, 'fetching user');

  try {
    const user = await getUser(req.params.id);
    req.log.debug({ user: user.id }, 'user found');
    res.json(user);
  } catch (error) {
    req.log.error({ error }, 'failed to fetch user');
    res.status(500).json({ error: 'Internal error' });
  }
});

Log Levels

// Log level guidelines
logger.trace('Detailed debugging info');      // 10 - Very verbose
logger.debug('Debugging information');         // 20 - Debug mode only
logger.info('Normal operation events');        // 30 - Default level
logger.warn('Warning conditions');             // 40 - Potential issues
logger.error('Error conditions');              // 50 - Errors that need attention
logger.fatal('System-critical errors');        // 60 - System failure

// Contextual logging
logger.info({ orderId, userId, amount }, 'order placed');
logger.error({ error: err.message, stack: err.stack }, 'payment failed');
logger.warn({ retryCount, maxRetries }, 'retry attempt');