Add optional service replica selector (#19398)

When using a replicaset for the server (for redundancy purposes),
this allows to select which replica the service will talk to in
order to have a consistent view of the data.

Signed-off-by: rabadin <rvbadin@gmail.com>

stable/prometheus/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: prometheus
-version: 9.5.5
+version: 9.5.6
 appVersion: 2.13.1
 description: Prometheus is a monitoring system and time series database.
 home: https://prometheus.io/

stable/prometheus/README.md

@@ -313,6 +313,8 @@ Parameter | Description | Default
 `server.service.servicePort` | Prometheus server service port | `80`
 `server.service.sessionAffinity` | Session Affinity for server service, can be `None` or `ClientIP` | `None`
 `server.service.type` | type of Prometheus server service to create | `ClusterIP`
+`server.service.statefulsetReplica.enabled` | If true, send the traffic from the service to only one replica of the replicaset | `false`
+`server.service.statefulsetReplica.replica` | Which replica to send the traffice to | `0`
 `server.sidecarContainers` | array of snippets with your sidecar containers for prometheus server | `""`
 `serviceAccounts.alertmanager.create` | If true, create the alertmanager service account | `true`
 `serviceAccounts.alertmanager.name` | name of the alertmanager service account to use or create | `{{ prometheus.alertmanager.fullname }}`

stable/prometheus/templates/server-service.yaml

@@ -38,9 +38,13 @@ spec:
       nodePort: {{ .Values.server.service.nodePort }}
     {{- end }}
   selector:
+  {{- if and .Values.server.statefulSet.enabled .Values.server.service.statefulsetReplica.enabled }}
+    statefulset.kubernetes.io/pod-name: {{ .Release.Name }}-{{ .Values.server.name }}-{{ .Values.server.service.statefulsetReplica.replica }}
+  {{- else -}}
     {{- include "prometheus.server.matchLabels" . | nindent 4 }}
 {{- if .Values.server.service.sessionAffinity }}
   sessionAffinity: {{ .Values.server.service.sessionAffinity }}
 {{- end }}
+  {{- end }}
   type: "{{ .Values.server.service.type }}"
 {{- end -}}

stable/prometheus/values.yaml

@@ -858,6 +858,13 @@ server:
     sessionAffinity: None
     type: ClusterIP
 
+    ## If using a statefulSet (statefulSet.enabled=true), configure the
+    ## service to connect to a specific replica to have a consistent view
+    ## of the data.
+    statefulsetReplica:
+      enabled: false
+      replica: 0
+
   ## Prometheus server pod termination grace period
   ##
   terminationGracePeriodSeconds: 300