Make Prometheus cAdvisor metrics labels consistent

Prometheus requires that all metrics in the same family have the same
labels, so we arrange to supply blank strings for missing labels

See google/cadvisor#1704

Author: bboreham

pkg/kubelet/cadvisor/cadvisor_linux.go

@@ -74,21 +74,29 @@ func init() {
 }
 
 func containerLabels(c *cadvisorapi.ContainerInfo) map[string]string {
-	set := map[string]string{metrics.LabelID: c.Name}
+	// Prometheus requires that all metrics in the same family have the same labels,
+	// so we arrange to supply blank strings for missing labels
+	var name, image, podName, namespace, containerName string
 	if len(c.Aliases) > 0 {
-		set[metrics.LabelName] = c.Aliases[0]
-	}
-	if image := c.Spec.Image; len(image) > 0 {
-		set[metrics.LabelImage] = image
+		name = c.Aliases[0]
 	}
+	image = c.Spec.Image
 	if v, ok := c.Spec.Labels[types.KubernetesPodNameLabel]; ok {
-		set["pod_name"] = v
+		podName = v
 	}
 	if v, ok := c.Spec.Labels[types.KubernetesPodNamespaceLabel]; ok {
-		set["namespace"] = v
+		namespace = v
 	}
 	if v, ok := c.Spec.Labels[types.KubernetesContainerNameLabel]; ok {
-		set["container_name"] = v
+		containerName = v
+	}
+	set := map[string]string{
+		metrics.LabelID:    c.Name,
+		metrics.LabelName:  name,
+		metrics.LabelImage: image,
+		"pod_name":         podName,
+		"namespace":        namespace,
+		"container_name":   containerName,
 	}
 	return set
 }

pkg/kubelet/server/server.go

@@ -816,21 +816,29 @@ func (a prometheusHostAdapter) GetMachineInfo() (*cadvisorapi.MachineInfo, error
 
 // containerPrometheusLabels maps cAdvisor labels to prometheus labels.
 func containerPrometheusLabels(c *cadvisorapi.ContainerInfo) map[string]string {
-	set := map[string]string{metrics.LabelID: c.Name}
+	// Prometheus requires that all metrics in the same family have the same labels,
+	// so we arrange to supply blank strings for missing labels
+	var name, image, podName, namespace, containerName string
 	if len(c.Aliases) > 0 {
-		set[metrics.LabelName] = c.Aliases[0]
-	}
-	if image := c.Spec.Image; len(image) > 0 {
-		set[metrics.LabelImage] = image
+		name = c.Aliases[0]
 	}
+	image = c.Spec.Image
 	if v, ok := c.Spec.Labels[kubelettypes.KubernetesPodNameLabel]; ok {
-		set["pod_name"] = v
+		podName = v
 	}
 	if v, ok := c.Spec.Labels[kubelettypes.KubernetesPodNamespaceLabel]; ok {
-		set["namespace"] = v
+		namespace = v
 	}
 	if v, ok := c.Spec.Labels[kubelettypes.KubernetesContainerNameLabel]; ok {
-		set["container_name"] = v
+		containerName = v
+	}
+	set := map[string]string{
+		metrics.LabelID:    c.Name,
+		metrics.LabelName:  name,
+		metrics.LabelImage: image,
+		"pod_name":         podName,
+		"namespace":        namespace,
+		"container_name":   containerName,
 	}
 	return set
 }