devops / monitoring
How to Learn Monitoring & Observability for Free
You can't fix what you can't see. Here's what monitoring and observability really mean, the open-source stack everyone uses — Prometheus, Grafana, OpenTelemetry — and how to know what's actually worth alerting on.
Once your software is running in production, a new question dominates: is it healthy, and if not, why? Monitoring tells you when something is wrong (a dashboard goes red, an alert fires). Observability goes further: it's how well you can understand why from the data your system emits, even for problems you didn't anticipate. The modern open-source stack is remarkably consistent across the industry: Prometheus collects metrics, Grafana visualizes them, and OpenTelemetry standardizes traces and logs. Learn these plus the principles of what to measure, and you can operate almost any system. This guide covers the concepts, the three pillars of data, the free resources, and the mistakes that lead to alert fatigue.
01 · WHAT IT IS
The three pillars of observability
Observable systems emit three kinds of data. Metrics are numbers over time — request rate, error rate, CPU usage — cheap to store and perfect for dashboards and alerts. Logs are timestamped records of discrete events, great for digging into the detail of what happened. Traces follow a single request as it hops across services, invaluable for finding where latency or errors originate in a distributed system.
Together they answer different questions: metrics tell you that something's wrong and how much, logs tell you what happened, and traces tell you where. Understanding which pillar answers which question is the mental model that makes all the tools make sense.
02 · THE PATH
The order to learn it in
Start with metrics — the highest-value, most approachable pillar. In order:
1. Metrics with Prometheus
How metrics are collected and queried. Learn PromQL (Prometheus's query language) and the idea of instrumenting your app to expose metrics. This is the backbone of modern monitoring.
2. Dashboards and alerts with Grafana
Turn those metrics into dashboards you can read at a glance, and alerts that fire when something crosses a threshold. Grafana sits on top of Prometheus (and much else).
3. Traces and logs, plus what to measure
Add OpenTelemetry for traces and logs, and — crucially — learn the SRE principles of what is worth alerting on, so you monitor signals that matter instead of noise.
03 · THE BEST FREE RESOURCES
Where to actually learn it (free)
Learn the open-source stack from its own docs, then the principles from Google's SRE book:
The stack. Prometheus is the de-facto standard for metrics and alerting in cloud-native systems — its docs teach PromQL, exporters, and alerting rules. Grafana turns metrics into dashboards and alerts on top of Prometheus and dozens of other sources. OpenTelemetry is the open standard for traces, metrics, and logs — instrument once, send telemetry anywhere.
- Prometheus Documentation (official) ↗The de-facto standard for metrics and alerting in cloud-native systems — learn PromQL, exporters, and alerting rules.prometheus.io
- Grafana Documentation (official) ↗Turn metrics into dashboards and alerts — the visualization layer that sits on top of Prometheus and dozens of other data sources.grafana.com
- OpenTelemetry (official docs) ↗The open standard for traces, metrics, and logs — instrument your code once and send telemetry anywhere.opentelemetry.io
What to measure. The Google SRE book's chapter on monitoring distributed systems explains the four golden signals and how to alert without drowning in noise. It's free and essential — the difference between monitoring that helps and monitoring that just annoys.
04 · AVOID THESE
Common mistakes learning monitoring
One trap is alerting on everything, which causes alert fatigue. When every metric pages you, you start ignoring alerts, including the real ones. Another is collecting data you never use: dashboards nobody looks at and metrics with no purpose. And some teams fall into monitoring internals instead of user experience, so their dashboards are green while customers are having a terrible time.
05 · TRY IT
Build a dashboard this weekend
Monitoring clicks the moment you watch a live metric from your own app move on a dashboard.
06 · FAQ
Frequently asked questions
What is the difference between monitoring and observability?
Monitoring tells you when something is wrong, typically through predefined dashboards and alerts. Observability is how well you can understand why something is wrong from the data your system emits, including for problems you did not anticipate. Observability is the broader capability.
What are the three pillars of observability?
The three pillars are metrics, logs, and traces. Metrics are numbers over time, logs are records of discrete events, and traces follow a single request across services. Together they answer whether something is wrong, what happened, and where.
Which monitoring tools should I learn first?
Learn Prometheus for metrics and Grafana for dashboards and alerts first, since they are the open-source standard and the highest-value starting point. Add OpenTelemetry for traces and logs once you are comfortable with metrics.
What are the four golden signals?
The four golden signals from Google's SRE practice are latency, traffic, errors, and saturation. Monitoring these user-facing and capacity signals gives you a focused, high-value view of a system's health without drowning in less meaningful metrics.
Can I learn monitoring and observability for free?
Yes. Prometheus, Grafana, and OpenTelemetry are free and open source with excellent documentation, and the Google SRE book is free to read online. You can run the whole stack locally with Docker to practice at no cost.