Add to migration doc steps regards changes over metrics to the scaffolded files.

doc/migration/version-upgrade-guide.md

@@ -812,6 +812,104 @@ See the [CHANGELOG](https://github.com/operator-framework/operator-sdk/blob/mast
 
 ## Unreleased
 
+### Bug Fixes and Improvements for Metrics
+
+There were some changes to the default implementation of the metrics export. These changes require the `cmd/main.go` be updated as follows.
+
+Replace:
+
+```
+func main() {
+    ...
+	// Add the Metrics Service
+	addMetrics(ctx, cfg, namespace)
+``` 
+
+With:
+
+```
+func main() {
+    ...
+	// Add the Metrics Service
+	addMetrics(ctx, cfg)
+``` 
+
+And then, update the default implementation of `addMetrics` and `serveCRMetrics` with:
+
+```go
+// addMetrics will create the Services and Service Monitors to allow the operator export the metrics by using
+// the Prometheus operator
+func addMetrics(ctx context.Context, cfg *rest.Config) {
+	// Get the namespace the operator is currently deployed in.
+	operatorNs, err := k8sutil.GetOperatorNamespace()
+	if err != nil {
+		if errors.Is(err, k8sutil.ErrRunLocal) {
+			log.Info("Skipping CR metrics server creation; not running in a cluster.")
+			return
+		}
+	}
+
+	if err := serveCRMetrics(cfg, operatorNs); err != nil {
+		log.Info("Could not generate and serve custom resource metrics", "error", err.Error())
+	}
+
+	// Add to the below struct any other metrics ports you want to expose.
+	servicePorts := []v1.ServicePort{
+		{Port: metricsPort, Name: metrics.OperatorPortName, Protocol: v1.ProtocolTCP, TargetPort: intstr.IntOrString{Type: intstr.Int, IntVal: metricsPort}},
+		{Port: operatorMetricsPort, Name: metrics.CRPortName, Protocol: v1.ProtocolTCP, TargetPort: intstr.IntOrString{Type: intstr.Int, IntVal: operatorMetricsPort}},
+	}
+
+	// Create Service object to expose the metrics port(s).
+	service, err := metrics.CreateMetricsService(ctx, cfg, servicePorts)
+	if err != nil {
+		log.Info("Could not create metrics Service", "error", err.Error())
+	}
+
+	// CreateServiceMonitors will automatically create the prometheus-operator ServiceMonitor resources
+	// necessary to configure Prometheus to scrape metrics from this operator.
+	services := []*v1.Service{service}
+
+	// The ServiceMonitor is created in the same namespace where the operator is deployed
+	_, err = metrics.CreateServiceMonitors(cfg, operatorNs, services)
+	if err != nil {
+		log.Info("Could not create ServiceMonitor object", "error", err.Error())
+		// If this operator is deployed to a cluster without the prometheus-operator running, it will return
+		// ErrServiceMonitorNotPresent, which can be used to safely skip ServiceMonitor creation.
+		if err == metrics.ErrServiceMonitorNotPresent {
+			log.Info("Install prometheus-operator in your cluster to create ServiceMonitor objects", "error", err.Error())
+		}
+	}
+}
+
+// serveCRMetrics gets the Operator/CustomResource GVKs and generates metrics based on those types.
+// It serves those metrics on "http://metricsHost:operatorMetricsPort".
+func serveCRMetrics(cfg *rest.Config, operatorNs string) error {
+	// The function below returns a list of filtered operator/CR specific GVKs. For more control, override the GVK list below
+	// with your own custom logic. Note that if you are adding third party API schemas, probably you will need to
+	// customize this implementation to avoid permissions issues.
+	filteredGVK, err := k8sutil.GetGVKsFromAddToScheme(apis.AddToScheme)
+	if err != nil {
+		return err
+	}
+
+	// The metrics will be generated from the namespaces which are returned here.
+	// NOTE that passing nil or an empty list of namespaces in GenerateAndServeCRMetrics will result in an error.
+	ns, err := kubemetrics.GetNamespacesForMetrics(operatorNs)
+	if err != nil {
+		return err
+	}
+
+	// Generate and serve custom resource specific metrics.
+	err = kubemetrics.GenerateAndServeCRMetrics(cfg, ns, filteredGVK, metricsHost, operatorMetricsPort)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+```
+
+**NOTE**: For more information check the PRs which are responsible for the above changes [#2606](https://github.com/operator-framework/operator-sdk/pull/2606),[#2603](https://github.com/operator-framework/operator-sdk/pull/2603) and [#2601](https://github.com/operator-framework/operator-sdk/pull/2601).
+
 ### Breaking changes
 
 #### Remove Ansible container sidecar