Tool cheatsheet

Prometheus and PromQL 3 Cheatsheet

Query metrics with PromQL, and configure scraping, recording rules, alerts and the promtool checker.

Selecting data

Select a metric — Return the current value of every series with this metric name.
Filter by labels — Match labels exactly with = and !=, or by regular expression with =~ and !~.
Select a range of samples — Return the samples from the last five minutes. Range vectors are the input to functions such as rate.
Look back in time — Compare with the value from an hour ago.
Find targets that are down — The up metric is 1 when the last scrape worked and 0 when it failed.

Per-second rate of a counter — Average per-second increase over five minutes. Always use rate (or increase) on counters, never the raw value.
Total increase over a window — How much a counter grew in the last hour.
Aggregate across series — Sum the rate across all instances, keeping one series per job and status.
Error ratio — The share of requests that fail, from two aggregated rates.
95th percentile latency — Estimate a percentile from a histogram's buckets. Always sum by le first.
Top N series — Return the five busiest series.
Average over time — Smooth a gauge by averaging over a window.
Predict a trend — Estimate free disk space four hours from now by extrapolating the last six hours.
Detect a missing metric — Returns 1 when no series match, which is useful for alerting on vanished targets.
Memory used as a percentage — A common node_exporter query for host memory use.
CPU used as a percentage — A common node_exporter query for host CPU use.

Scrape targets — A minimal prometheus.yml that scrapes itself and an application every 15 seconds.
Precompute an expensive query — A recording rule stores a query's result as a new metric, so dashboards stay fast.
Define an alert — Fire when the error ratio stays above 5% for ten minutes.
Route alerts — An Alertmanager configuration that groups alerts and sends pages to one receiver.

Start Prometheus — Run Prometheus with a config file. The UI is at http://localhost:9090.
Check the configuration — Validate prometheus.yml and the rule files it references before reloading.
Check rule files — Validate the syntax of recording and alerting rules.
Unit-test alert rules — Run tests that supply sample series and check which alerts fire.
Reload the configuration — Reload without restarting. It needs --web.enable-lifecycle, or send SIGHUP.
Query over HTTP — Run an instant query against the HTTP API.
Query from the command line — Run an instant query with promtool.
List scrape targets — See the health of every target through the API.

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