Monitoring Expert

Logging (Node.js)

// Using Pino (fast) import pino from 'pino';

const logger = pino({ level: process.env.LOG_LEVEL || 'info', transport: process.env.NODE_ENV !== 'production' ? { target: 'pino-pretty' } : undefined });

// Usage logger.info({ userId: 123 }, 'User logged in'); logger.error({ err, requestId }, 'Failed to process');

// Express middleware import pinoHttp from 'pino-http'; app.use(pinoHttp({ logger }));

Error Tracking (Sentry)

import * as Sentry from '@sentry/node';

Sentry.init({ dsn: process.env.SENTRY_DSN, environment: process.env.NODE_ENV, tracesSampleRate: 0.1, });

// Capture errors try { riskyOperation(); } catch (error) { Sentry.captureException(error); throw error; }

// Express error handler app.use(Sentry.Handlers.errorHandler());

Health Checks

// /health endpoint app.get('/health', async (req, res) => { const health = { status: 'ok', timestamp: new Date().toISOString(), uptime: process.uptime(), checks: { database: await checkDatabase(), redis: await checkRedis(), } };

const isHealthy = Object.values(health.checks).every(v => v === 'ok'); res.status(isHealthy ? 200 : 503).json(health); });

async function checkDatabase() { try { await prisma.$queryRawSELECT 1; return 'ok'; } catch { return 'error'; } }

Metrics (Prometheus)

import promClient from 'prom-client';

// Default metrics promClient.collectDefaultMetrics();

// Custom metrics const httpRequestDuration = new promClient.Histogram({ name: 'http_request_duration_seconds', help: 'HTTP request duration', labelNames: ['method', 'route', 'status'], });

// Middleware app.use((req, res, next) => { const end = httpRequestDuration.startTimer(); res.on('finish', () => { end({ method: req.method, route: req.path, status: res.statusCode }); }); next(); });

// Endpoint app.get('/metrics', async (req, res) => { res.set('Content-Type', promClient.register.contentType); res.end(await promClient.register.metrics()); });

Quick Debug Commands

Check logs

journalctl -u myapp -f --since "1 hour ago" docker logs -f --tail 100 container_name

Check resources

htop df -h free -m

Network

netstat -tlnp ss -tlnp curl -I http://localhost:3000/health