[collector] add node ip to kubeletstats

In some scenarios, it's desirable to use the node IP instead of the node name to gather kubelet metrics.
This commit makes it possible for the user to specify the `presets.kubeletMetrics.useNodeIp` flag
so that the node ip is used as an endpoint instead of the node name.

charts/opentelemetry-collector/templates/_config.tpl

@@ -168,7 +168,11 @@ receivers:
   kubeletstats:
     collection_interval: 20s
     auth_type: "serviceAccount"
+    {{- if .Values.presets.kubeletMetrics.useNodeIp }}
+    endpoint: "${env:K8S_NODE_IP}:10250"
+    {{- else }}
     endpoint: "${env:K8S_NODE_NAME}:10250"
+    {{- end }}
 {{- end }}
 
 {{- define "opentelemetry-collector.applyLogsCollectionConfig" -}}

charts/opentelemetry-collector/templates/_pod.tpl

@@ -56,6 +56,10 @@ containers:
         valueFrom:
           fieldRef:
             fieldPath: spec.nodeName
+      - name: K8S_NODE_IP
+        valueFrom:
+          fieldRef:
+            fieldPath: status.hostIp
       {{- end }}
       {{- if and (.Values.useGOMEMLIMIT) ((((.Values.resources).limits).memory))  }}
       - name: GOMEMLIMIT

charts/opentelemetry-collector/values.yaml

@@ -62,6 +62,9 @@ presets:
   # See https://opentelemetry.io/docs/kubernetes/collector/components/#kubeletstats-receiver for details on the receiver.
   kubeletMetrics:
     enabled: false
+    # Instead of using the K8s Node name to gather kubelet metrics, use it's IP.
+    # This can be useful when running the collector on k8s clusters where the node name isn't resovled in pods
+    useNodeIp: false
   # Configures the collector to collect kubernetes events.
   # Adds the k8sobject receiver to the logs pipeline
   # and collects kubernetes events by default.