Observability Fundamentals
Logs, metrics, and traces - the three pillars that let you understand a system you didn't build yourself.
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Monitoring tells you that something is wrong - a dashboard goes red, an alert fires. Observability is the deeper property that lets you figure out why, even for a question nobody thought to ask in advance.
The three pillars
| Pillar | What it captures | Good for |
|---|---|---|
| Logs | Discrete, timestamped events ("user 42 logged in") | The detailed story of exactly what happened |
| Metrics | Numbers over time (CPU %, requests/sec) | Spotting trends, triggering alerts |
| Traces | The path one request takes across services | Finding where in a chain of calls time went |
No single pillar tells the whole story alone - a metric tells you requests got slow at 2:14 PM, a trace tells you which downstream service in the chain was the slow one, and a log tells you the exact error it hit.
Can you answer a question you didn't anticipate?
That's the real test of observability. A system with only a handful of pre-built dashboards can answer the questions its author thought of in advance. A genuinely observable system lets you ask something brand new - "which customers hit this rare error path last Tuesday?" - and actually get an answer, because the underlying data was captured richly enough to slice in ways nobody planned for ahead of time.
Where to start
You don't need all three pillars perfectly wired up on day one. A sensible order:
- Logs first - cheapest to get started with, and the most detail per event.
- Metrics next - for trends and alerting on sustained problems.
- Traces once you have more than a couple of services calling each other.
Try it
A single number already tells you something about a system's health:
uptime
When you're ready, hit Mark complete and move to the next lesson.
Challenge
Check how long this machine has been running and its current load average.
Want to experiment first? Try things in the practice terminal (opens in a new tab), then enter the command that solves the task here.
Quiz
Lock in the concepts. Score at least 80% to mark the lesson complete.
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