fix(inputs.promethes): respect selectors when scraping pods (#12278)

plugins/inputs/prometheus/prometheus.go

@@ -134,7 +134,14 @@ func (p *Prometheus) Init() error {
 
 			p.NodeIP = envVarNodeIP
 		}
+		p.Log.Infof("Using pod scrape scope at node level to get pod list using cAdvisor.")
+	}
 
+	if p.MonitorKubernetesPodsMethod == MonitorMethodNone {
+		p.MonitorKubernetesPodsMethod = MonitorMethodAnnotations
+	}
+
+	if p.isNodeScrapeScope || p.MonitorKubernetesPodsMethod != MonitorMethodAnnotations {
 		// Parse label and field selectors - will be used to filter pods after cAdvisor call
 		var err error
 		p.podLabelSelector, err = labels.Parse(p.KubernetesLabelSelector)
@@ -150,14 +157,9 @@ func (p *Prometheus) Init() error {
 			return fmt.Errorf("the field selector %s is not supported for pods", invalidSelector)
 		}
 
-		p.Log.Infof("Using pod scrape scope at node level to get pod list using cAdvisor.")
 		p.Log.Infof("Using the label selector: %v and field selector: %v", p.podLabelSelector, p.podFieldSelector)
 	}
 
-	if p.MonitorKubernetesPodsMethod == MonitorMethodNone {
-		p.MonitorKubernetesPodsMethod = MonitorMethodAnnotations
-	}
-
 	ctx := context.Background()
 	client, err := p.HTTPClientConfig.CreateClient(ctx, p.Log)
 	if err != nil {

plugins/inputs/prometheus/prometheus_test.go

@@ -326,3 +326,22 @@ func TestInitConfigErrors(t *testing.T) {
 	expectedMessage = "the field selector spec.containerNames is not supported for pods"
 	require.Error(t, err, expectedMessage)
 }
+
+func TestInitConfigSelectors(t *testing.T) {
+	p := &Prometheus{
+		MetricVersion:               2,
+		Log:                         testutil.Logger{},
+		URLs:                        nil,
+		URLTag:                      "url",
+		MonitorPods:                 true,
+		MonitorKubernetesPodsMethod: MonitorMethodSettings,
+		PodScrapeInterval:           60,
+		KubernetesLabelSelector:     "app=test",
+		KubernetesFieldSelector:     "spec.nodeName=node-0",
+	}
+	err := p.Init()
+	require.NoError(t, err)
+
+	require.NotNil(t, p.podLabelSelector)
+	require.NotNil(t, p.podFieldSelector)
+}