[exporter/loadbalancingexporter] add docs/example for k8s service re…

…solver (#24362)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
improve document for k8s service resolver of
exporter/loadbalancingexporter

**Link to tracking Issue:** <Issue number if applicable>
#24287 

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>
Add example/k8s-resolver/README.md
The description of the k8s resolver from
exporter/loadbalancingexporter/README.md can be jump-linked to example.

Signed-off-by: Yuan Fang <yuanfang@alauda.io>

.chloggen/add-k8s-resolver-docs.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: loadbalancingexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Added docs for k8s service resolver.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [24287]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

exporter/loadbalancingexporter/README.md

@@ -97,7 +97,7 @@ service:
         - loadbalancing
 ```
 
-Kubernetes resolver example
+Kubernetes resolver example (For a more specific example: [example/k8s-resolver](./example/k8s-resolver/README.md))
 ```yaml
 receivers:
   otlp:

exporter/loadbalancingexporter/example/k8s-resolver/README.md

@@ -0,0 +1,121 @@
+# Trace ID aware load-balancing exporter demo for kubernetes service resolver
+
+## How to run
+
+1. Pre-requirements:
+```shell
+kubectl apply -f https://github.com/open-telemetry/opentelemetry-operator/releases/latest/download/opentelemetry-operator.yaml
+```
+
+2. Once the opentelemetry-operator is deployed, create the OpenTelemetry Collector (otelcol) instances, ServiceAccount and other necessary resources, run:
+```shell
+kubectl apply -f - <<EOF
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: observability
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: loadbalancer-role
+  namespace: observability
+rules:
+- apiGroups:
+  - ""
+  resources:
+  - endpoints
+  verbs:
+  - list
+  - watch
+  - get
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: loadbalancer
+  namespace: observability
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: loadbalancer-rolebinding
+  namespace: observability
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: Role
+  name: loadbalancer-role
+subjects:
+- kind: ServiceAccount
+  name: loadbalancer
+  namespace: observability
+---
+apiVersion: opentelemetry.io/v1alpha1
+kind: OpenTelemetryCollector
+metadata:
+  name: loadbalancer
+  namespace: observability
+spec:
+  image: docker.io/jpkroehling/otelcol-with-k8sresolver:latest
+  serviceAccount: loadbalancer
+  config: |
+    receivers:
+      otlp:
+        protocols:
+          grpc:
+
+    processors:
+
+    exporters:
+      loadbalancing:
+        protocol:
+          otlp:
+            tls:
+              insecure: true
+        resolver:
+          k8s:
+            service: backends-collector-headless.observability
+
+    service:
+      pipelines:
+        traces:
+          receivers:
+            - otlp
+          processors: []
+          exporters:
+            - loadbalancing
+---
+apiVersion: opentelemetry.io/v1alpha1
+kind: OpenTelemetryCollector
+metadata:
+  name: backends
+  namespace: observability
+spec:
+  replicas: 5
+  config: |
+    receivers:
+      otlp:
+        protocols:
+          grpc:
+
+    processors:
+
+    exporters:
+      logging:
+
+    service:
+      pipelines:
+        traces:
+          receivers:
+            - otlp
+          processors: []
+          exporters:
+            - logging
+EOF
+```
+
+## How does it work
+- The `loadbalancer` and `backends` OpenTelemetryCollector are recognised by the opentelemetry-operator, which then creates the appropriate deployment resources.
+- The `loadbalancer` ServiceAccount is used to assign to the pods corresponding to the deployment loadbalancer and backends.
+- The `loadbalancer-role` Role grants `get`, `list`, and `watch` permissions on endpoint resources in its namespace. Having these permissions is essential for a kubernetes service resolver to work properly.
+- The `loadbalancer-rolebinding` RoleBinding is used to bind Role `loadbalancer-role` to ServiceAccount `loadbalancer`.