PromQL basics

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 path

Counters 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_replicas

Queries are run in the Prometheus UI or with the /api/v1/query HTTP API.

Exercise 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.

Show example 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]))'

Test yourself

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
Show answer

The total increase in requests over the last hour — increase ≈ rate × the range duration.

Calculate the per-second rate for a counter.

____(http_requests_total[5m])

Show answer

rate(http_requests_total[5m])

Match.

{status="500"}

Equality filter
{status=~"5.."}

Regex filter
[5m]

Time range
sum by (path)

Grouped sum

Next lesson: Alertmanager

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