docs(prometheus): Document how to set up scraping in kubernetes

docs/source/administrator/troubleshooting.md

@@ -24,3 +24,26 @@ managing cost with JupyterHub, see {ref}`cost`.
 Each Helm Chart is packaged with a specific version of JupyterHub (and
 other software as well). See see the [Helm Chart repository](https://github.com/jupyterhub/helm-chart#release-notes)
 for information about the versions of relevant software packages.
+
+## Metrics scraping with prometheus or vmagent
+
+Network policy needs to be modified in order for prometheus or vmagent to be able to reach the metrics endpoint. Working example configuration is as follows:
+
+```yaml
+hub:
+  annotations:
+    prometheus.io/scrape: "true"
+    prometheus.io/path: "/hub/metrics"
+    prometheus.io/port: "8081"
+  networkPolicy:
+    ingress:
+      - from:
+          - namespaceSelector:
+              matchLabels:
+                # namespace where your prometheus or vmagent is running
+                name: victoriametrics
+          - podSelector:
+              matchLabels:
+                # a valid selector for the pod that needs to reach jupyterhub
+                app.kubernetes.io/instance: vmagent
+```

jupyterhub/values.yaml

@@ -109,6 +109,16 @@ hub:
     minAvailable: 1
   networkPolicy:
     enabled: true
+    # To open for vmagent to scrape metrics from the hub pod, add the following
+    # to the ingress list:
+    # ingress:
+    # - from:
+    #   - namespaceSelector:
+    #       matchLabels:
+    #         name: victoriametrics
+    #   - podSelector:
+    #       matchLabels:
+    #         app.kubernetes.io/instance: vmagent
     ingress: []
     egress: []
     egressAllowRules: