Logging Best Practices: Fehler finden und verstehen

Gutes Logging ist die Basis für Debugging und Monitoring. Lernen Sie, wie Sie effektiv loggen ohne in Daten zu ertrinken.

Log Levels

Was loggen?

Strukturiertes Logging (JSON)

// ❌ Unstrukturiert (schwer zu parsen)
console.log('User 123 logged in from 192.168.1.1 at 2024-01-15 10:30:00');

// ✅ Strukturiert (JSON)
{
  "timestamp": "2024-01-15T10:30:00.000Z",
  "level": "info",
  "message": "User logged in",
  "userId": 123,
  "ip": "192.168.1.1",
  "userAgent": "Mozilla/5.0...",
  "requestId": "abc-123-def"
}

PHP: Monolog

composer require monolog/monolog

<?php
use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Monolog\Handler\RotatingFileHandler;
use Monolog\Formatter\JsonFormatter;

// Logger erstellen
$log = new Logger('app');

// Handler für verschiedene Outputs
$log->pushHandler(new StreamHandler('php://stdout', Logger::DEBUG));
$log->pushHandler(new RotatingFileHandler('/var/log/app/app.log', 14, Logger::INFO));

// JSON-Format
$handler = new StreamHandler('/var/log/app/app.json', Logger::INFO);
$handler->setFormatter(new JsonFormatter());
$log->pushHandler($handler);

// Logging
$log->info('User logged in', ['userId' => 123, 'ip' => $_SERVER['REMOTE_ADDR']]);
$log->error('Database error', ['exception' => $e->getMessage()]);

Node.js: Winston

npm install winston

const winston = require('winston');

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

// In Development auch Console
if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.simple(),
  }));
}

// Logging
logger.info('Server started', { port: 3000 });
logger.error('Database connection failed', { error: err.message });

Python: logging

import logging
import json

# JSON Formatter
class JsonFormatter(logging.Formatter):
    def format(self, record):
        log_record = {
            'timestamp': self.formatTime(record),
            'level': record.levelname,
            'message': record.getMessage(),
            'module': record.module,
        }
        if record.exc_info:
            log_record['exception'] = self.formatException(record.exc_info)
        return json.dumps(log_record)

# Logger konfigurieren
logger = logging.getLogger('app')
logger.setLevel(logging.DEBUG)

handler = logging.StreamHandler()
handler.setFormatter(JsonFormatter())
logger.addHandler(handler)

# Logging
logger.info('User logged in', extra={'userId': 123})
logger.error('Database error', exc_info=True)

Request ID / Correlation ID

Eine ID pro Request für zusammenhängende Logs:

// Middleware: Request ID generieren
app.use((req, res, next) => {
  req.requestId = req.headers['x-request-id'] || uuid();
  res.setHeader('x-request-id', req.requestId);
  next();
});

// Bei jedem Log mitgeben
logger.info('Processing order', {
  requestId: req.requestId,
  orderId: order.id
});

// So können alle Logs einer Anfrage gefunden werden:
// grep "abc-123-def" combined.log

Log Rotation

# /etc/logrotate.d/myapp
/var/log/myapp/*.log {
    daily
    rotate 14
    compress
    delaycompress
    missingok
    notifempty
    create 0640 www-data www-data
    postrotate
        systemctl reload myapp
    endscript
}

Zentrales Logging

Bei mehreren Servern: Logs zentral sammeln

• ELK Stack: Elasticsearch, Logstash, Kibana
• Loki + Grafana: Leichtgewichtiger
• Cloud: CloudWatch, Stackdriver, Papertrail

Log-Meldungen formulieren

// ❌ Schlecht
logger.error('Error');
logger.info('Done');
logger.debug('Here');

// ✅ Gut
logger.error('Failed to send email', {
  recipient: email,
  error: err.message,
  retryCount: 3
});

logger.info('Order processed successfully', {
  orderId: order.id,
  total: order.total,
  processingTime: endTime - startTime
});

Weitere Informationen

• 📊 Prometheus Metriken
• 📈 Grafana Dashboards
• 🔧 Logrotate einrichten
• 📊 Enjyn Server Monitor