Module Overview

What You’ll Learn

• Explain the difference between logs, metrics, and traces, and what each is actually for
• Instrument an Express app with Prometheus-style metrics
• Explain what an uptime check and an alert actually automate

💡 Why this matters: Course 3’s structured logging (Module 9) makes an individual failure visible, after it happens, to someone reading logs. Metrics answer a different question, not “what went wrong in this one request” but “how is the whole system behaving, right now, and is it getting worse.”

What’s Covered

• Logs versus metrics versus traces, three distinct kinds of observability data, each answering a different question.
• Prometheus-style metrics, counters, gauges, and histograms, instrumented directly in an Express app.
• A /metrics endpoint, exposing application metrics for a monitoring system to collect.
• Uptime checks and alerting, what actually notices an application is down, and how a team finds out.

Hands-On

By the end of this module, you’ll have a real /metrics endpoint on a running Express app, reporting real request counts and response times.

This is the final module before the course capstone, deploying a complete, production-ready API, start to finish.