Observability: Logging, Tracing, Metrics

Overview

Observability enables understanding complex systems through data - logs, traces, and metrics. Build systems that are easy to debug and monitor.

Three Pillars

• Logs: Records of discrete events
• Traces: End-to-end request tracking
• Metrics: Numeric measurements over time

Logging with Winston

npm install winston

import winston from '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' }),
    new winston.transports.Console({
      format: winston.format.simple()
    })
  ]
})

logger.info('Server started', { port: 3000 })
logger.error('Database connection failed', { error: 'ECONNREFUSED' })

Distributed Tracing with OpenTelemetry

npm install @opentelemetry/api @opentelemetry/sdk-node @opentelemetry/sdk-trace-node

import { NodeTracerProvider } from '@opentelemetry/sdk-trace-node'
import { registerInstrumentations } from '@opentelemetry/instrumentation'

const provider = new NodeTracerProvider()
provider.register()

const tracer = provider.getTracer('my-app')

const span = tracer.startSpan('processOrder')
try {
  // Do work
  span.addEvent('order_processed', { orderId: 123 })
} finally {
  span.end()
}

Metrics with Prometheus

npm install prom-client

import { register, Counter, Histogram, Gauge } from 'prom-client'

const requestCounter = new Counter({
  name: 'http_requests_total',
  help: 'Total HTTP requests',
  labelNames: ['method', 'route', 'status']
})

const requestDuration = new Histogram({
  name: 'http_request_duration_seconds',
  help: 'HTTP request latency',
  labelNames: ['method', 'route']
})

const activeConnections = new Gauge({
  name: 'active_connections',
  help: 'Number of active connections'
})

// Express middleware
app.use((req, res, next) => {
  const start = Date.now()
  activeConnections.inc()

  res.on('finish', () => {
    const duration = (Date.now() - start) / 1000
    requestCounter.labels(req.method, req.route.path, res.statusCode).inc()
    requestDuration.labels(req.method, req.route.path).observe(duration)
    activeConnections.dec()
  })

  next()
})

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

Proper observability reduces mean-time-to-resolution (MTTR) by 80%.