Prometheus & Observability
Metrics, PromQL and alerting explained from first principles. Learn how Prometheus scrapes, stores and queries time series — and remember it with spaced repetition.
- flashcards
- 76
- flashcards
- per day
- ~10 min
- per day
- level
- Beginner → Intermediate
- level
- modules
- 5
- modules
What is Prometheus?
Prometheus is an open-source monitoring system built around a pull model: it scrapes numeric metrics from instrumented targets over HTTP and stores them as time series, each identified by a metric name and a set of labels.
On top of that data sits PromQL, a query language for slicing, aggregating and computing rates over those series — the engine behind dashboards, recording rules and alerts. Knowing the difference between a counter and a gauge, or rate() and irate(), is what separates dashboards that lie from dashboards you can trust.
This track covers the whole loop — exposition format and exporters, the four metric types, PromQL, and alerting through Alertmanager — and uses spaced repetition so the concepts stick when you are on call and need them most.
Studying for the certification? The modules here line up with the five Prometheus Certified Associate exam domains, and that guide walks each one — including the domain that is barely about Prometheus at all.
5 modules, seed to bloom
Each module is a set of flashcards — 76 in total. Answer, review, and watch your knowledge grow from seed to full bloom.
Observability Concepts
Metrics, logs and traces, golden signals, SLI/SLO/SLA, and the pull model
12 cardsPrometheus Fundamentals
Architecture, the TSDB, scraping and service discovery, metric types, and exposition
15 cardsPromQL
Vectors and selectors, rate functions, aggregation, histogram_quantile, and operators
23 cardsInstrumentation & Exporters
Client libraries, exporters, the Pushgateway, naming conventions, and label practices
12 cardsAlerting & Dashboarding
Alerting and recording rules, the for clause, Alertmanager routing, and dashboard queries
14 cardsSample questions
A taste of the real flashcards. Pick an answer, then reveal the explanation.
Prometheus starts with no exporters. What can you query already?
- AIts own prometheus_* metrics — the server scrapes itself
- BNothing at all — the TSDB stays empty until a target is added
- CHost metrics — the server collects CPU and memory by itself
- DOnly up — the one series the server maintains without targets
What does http_requests_total return with no brackets?
- AOne sample per matching series — an instant vector
- BEvery sample — the last five minutes of each series
- COne number — the total across every matching series
- DThe names alone — the series come back without values
How does your own service come to expose a request counter?
- AA client library — it maintains the metrics and serves /metrics
- BAn exporter sidecar — it derives the counter from the logs
- CA scrape config — the server counts the requests it observes
- DA recording rule — it builds the counter from existing series
An alert rule returns 3 series. How many alerts does it fire?
- AThree — one alert per returned label set, with its own state
- BOne — the rule is the alert, and the series are its evidence
- COne per rule group — related rules merge into one alert
- DNone until they agree — a rule needs a single clear result
Learn it once, keep it for good
Answer a question
Each card is one practical concept with multiple options. Pick what you think is right.
Get the full answer
See the correct option plus a clear explanation, and a link to deeper docs when one is available.
Review at the right time
A spaced-repetition engine (SM-2 or FSRS) resurfaces each card just before you would forget it.
Why Prometheus is worth your time
The de-facto cloud-native monitoring stack
Prometheus is the metrics backbone of Kubernetes and most modern infra. Fluency here is a core SRE skill.
Query data with confidence
Understanding PromQL and metric types means your alerts fire on real problems, not noise.
Instrument the right way
Knowing counters, gauges, histograms and summaries lets you expose metrics that actually answer questions.
Interview-ready
PromQL, the pull model and alerting design are staple observability and SRE interview topics.
Common questions
Do I need monitoring experience? +
No. The track starts from the pull model and metric types, so beginners and engineers formalizing what they already half-know both benefit.
Does it cover PromQL? +
Yes — PromQL is the largest module, covering instant vs range vectors, rate/increase, aggregation, histograms and common pitfalls.
Is it free? +
Yes, completely free. No registration or credit card is required, and all your progress is stored locally in your browser.
Will this prepare me for the PCA exam? +
It is not an exam dump, but it covers the conceptual core the Prometheus Certified Associate tests, and pairs well with hands-on practice.
Ready to master Prometheus?
Plant your first seed today. Ten minutes a day is all it takes to turn metrics into monitoring you can trust.