fix dashboard rate interval

Author: ppalucki

deployment/pcm/README.md

@@ -249,7 +249,14 @@ promtool query instant http://127.0.0.1:8001/api/v1/namespaces/default/services/
 
 # 1) Download dashboard
 curl -Ls http://127.0.0.1:8001/api/v1/namespaces/default/pods/$podname/proxy/dashboard/prometheus -o pcm-dashboard.json
-sed -i 's/4s/2m/' pcm-dashboard.json
+
+# change default (too small) interval (from 4s to 2m, following Prometheus best practicies of rate being four times larger than scrapping 30s)
+# References: 
+# https://grafana.com/blog/2020/09/28/new-in-grafana-7.2-__rate_interval-for-prometheus-rate-queries-that-just-work/
+# ($__rate_interval is 4 x scrape interval defined in datasource provisioned by prometheus operator, scrape internval is based on Prometheus object which defaults to 30s)
+# - https://github.com/prometheus-community/helm-charts/blob/main/charts/kube-prometheus-stack/values.yaml#L1069
+# - https://github.com/prometheus-community/helm-charts/blob/main/charts/kube-prometheus-stack/values.yaml#L3381
+sed -i 's/4s/$__rate_interval/g' pcm-dashboard.json
 
 # 2) port forward with kubectl (--address=0.0.0.0)
 kubectl port-forward -n default service/prometheus-grafana 8002:80 
@@ -258,9 +265,9 @@ kubectl port-forward -n default service/prometheus-grafana 8002:80
 # or get password kubectl get secret --namespace default prometheus-grafana -o jsonpath="{.data.admin-password}" | base64 --decode ; echo
 http://127.0.0.1:8002
 
-# 4) Go to Dashboards/New/Import 
+# 4) Go to Dashboards/New/Import  and upload:
+
 pcm-dashboard.json
-# and open
 
 ```