DevOps Lesson 10: Monitoring & Observability

You can’t fix what you can’t see. Monitoring tells you when things break; observability tells you WHY they broke. Both are essential in production.

The Three Pillars

// 1. METRICS: numerical measurements over time
// CPU usage, memory, request count, error rate, latency
// Tools: Prometheus, Datadog, CloudWatch

// 2. LOGS: timestamped events
// What happened? When? With what data?
// Tools: ELK Stack (Elasticsearch+Logstash+Kibana), Loki, Papertrail

// 3. TRACES: request journey through system
// User request → API → DB → Cache → ... how long each step?
// Tools: Jaeger, Zipkin, DataDog APM

Add Metrics to Node.js

// npm install prom-client
const prometheus = require("prom-client");
const register = new prometheus.Registry();
prometheus.collectDefaultMetrics({ register });

// Custom metrics
const httpRequestDuration = new prometheus.Histogram({
  name: "http_request_duration_seconds",
  help: "Duration of HTTP requests in seconds",
  labelNames: ["method", "route", "status"],
  buckets: [0.1, 0.5, 1, 2, 5]
});
register.registerMetric(httpRequestDuration);

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

// Expose metrics for Prometheus to scrape
app.get("/metrics", async (req, res) => {
  res.set("Content-Type", register.contentType);
  res.end(await register.metrics());
});