PromQL basics
- Docker & Kubernetes course
- Advanced
- Lesson 52/70
- 4 min
Learn to query metrics with PromQL.
PromQL basics
PromQL is Prometheus's query language. A metric name selects all series, label filters a subset; [5m] is a time range:
http_requests_total # all series
http_requests_total{status="500"} # equality
http_requests_total{status=~"5.."} # regular expression
rate(http_requests_total[5m]) # per-second increase
sum by (path) (rate(http_requests_total[5m])) # total per pathCounters are always used with rate() or increase(); the raw value resets on restart.
Kubernetes metrics
kube-prometheus-stack also collects cAdvisor (container resources) and kube-state-metrics (object state) metrics:
# CPU usage per namespace (cores)
sum by (namespace) (rate(container_cpu_usage_seconds_total[5m]))
# containers that restarted
increase(kube_pod_container_status_restarts_total[1h]) > 0
# deployments with unavailable replicas
kube_deployment_status_replicas_available < kube_deployment_spec_replicasQueries are run in the Prometheus UI or with the /api/v1/query HTTP API.
Practice Query via the API
Write two commands: forward the svc/izleme-kube-prometheus-sta-prometheus service in izleme from local 9090 to 9090; then send --data-urlencode 'query=sum(rate(http_requests_total[5m]))' to the http://localhost:9090/api/v1/query endpoint with curl -s.
Starter code
# buraya yazSample solution
kubectl port-forward -n izleme svc/izleme-kube-prometheus-sta-prometheus 9090:9090
curl -s http://localhost:9090/api/v1/query --data-urlencode 'query=sum(rate(http_requests_total[5m]))'Expected output
Forwarding from 127.0.0.1:9090 -> 9090
{"status":"success","data":{"resultType":"vector","result":[{"metric":{},"value":[1793710800,"42.7"]}]}}
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does increase(http_requests_total[1h]) give?
- The per-second rate
- The counter's raw value
- The value an hour ago
- The total increase in requests over the last hour Correct answer
Explanation: increase ≈ rate × the range duration.
2 Calculate the per-second rate for a counter.
____(http_requests_total[5m])rate(http_requests_total[5m])Explanation: rate is the counter's average increase speed over the range.
3 Match.
| Term | Meaning |
|---|---|
{status="500"} |
Equality filter |
{status=~"5.."} |
Regex filter |
[5m] |
Time range |
sum by (path) |
Grouped sum |