Add label and field selectors to prometheus input k8s discovery (#6969)

plugins/inputs/prometheus/kubernetes_test.go

@@ -1,6 +1,7 @@
 package prometheus
 
 import (
+	"github.com/ericchiang/k8s"
 	"testing"
 
 	"github.com/influxdata/telegraf/testutil"
@@ -95,8 +96,54 @@ func TestDeletePods(t *testing.T) {
 	assert.Equal(t, 0, len(prom.kubernetesPods))
 }
 
+func TestPodSelector(t *testing.T) {
+
+	cases := []struct {
+		expected      []k8s.Option
+		labelselector string
+		fieldselector string
+	}{
+		{
+			expected: []k8s.Option{
+				k8s.QueryParam("labelSelector", "key1=val1,key2=val2,key3"),
+				k8s.QueryParam("fieldSelector", "spec.nodeName=ip-1-2-3-4.acme.com"),
+			},
+			labelselector: "key1=val1,key2=val2,key3",
+			fieldselector: "spec.nodeName=ip-1-2-3-4.acme.com",
+		},
+		{
+			expected: []k8s.Option{
+				k8s.QueryParam("labelSelector", "key1"),
+				k8s.QueryParam("fieldSelector", "spec.nodeName=ip-1-2-3-4.acme.com"),
+			},
+			labelselector: "key1",
+			fieldselector: "spec.nodeName=ip-1-2-3-4.acme.com",
+		},
+		{
+			expected: []k8s.Option{
+				k8s.QueryParam("labelSelector", "key1"),
+				k8s.QueryParam("fieldSelector", "somefield"),
+			},
+			labelselector: "key1",
+			fieldselector: "somefield",
+		},
+	}
+
+	for _, c := range cases {
+		prom := &Prometheus{
+			Log:                     testutil.Logger{},
+			KubernetesLabelSelector: c.labelselector,
+			KubernetesFieldSelector: c.fieldselector,
+		}
+
+		output := podSelector(prom)
+
+		assert.Equal(t, len(output), len(c.expected))
+	}
+}
+
 func pod() *v1.Pod {
-	p := &v1.Pod{Metadata: &metav1.ObjectMeta{}, Status: &v1.PodStatus{}}
+	p := &v1.Pod{Metadata: &metav1.ObjectMeta{}, Status: &v1.PodStatus{}, Spec: &v1.PodSpec{}}
 	p.Status.PodIP = str("127.0.0.1")
 	p.Metadata.Name = str("myPod")
 	p.Metadata.Namespace = str("default")