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

plugins/inputs/prometheus/prometheus.go

@@ -15,6 +15,8 @@ import (
 	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/internal/tls"
 	"github.com/influxdata/telegraf/plugins/inputs"
+	"k8s.io/apimachinery/pkg/fields"
+	"k8s.io/apimachinery/pkg/labels"
 )
 
 const acceptHeader = `application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,*/*;q=0.1`
@@ -29,6 +31,12 @@ type Prometheus struct {
 	// Location of kubernetes config file
 	KubeConfig string
 
+	// Label Selector/s for Kubernetes
+	KubernetesLabelSelector string `toml:"kubernetes_label_selector"`
+
+	// Field Selector/s for Kubernetes
+	KubernetesFieldSelector string `toml:"kubernetes_field_selector"`
+
 	// Bearer Token authorization file path
 	BearerToken       string `toml:"bearer_token"`
 	BearerTokenString string `toml:"bearer_token_string"`
@@ -90,6 +98,11 @@ var sampleConfig = `
   ## Restricts Kubernetes monitoring to a single namespace
   ##   ex: monitor_kubernetes_pods_namespace = "default"
   # monitor_kubernetes_pods_namespace = ""
+  # label selector to target pods which have the label
+  # kubernetes_label_selector = "env=dev,app=nginx"
+  # field selector to target pods
+  # eg. To scrape pods on a specific node
+  # kubernetes_field_selector = "spec.nodeName=$HOSTNAME"
 
   ## Use bearer token for authorization. ('bearer_token' takes priority)
   # bearer_token = "/path/to/bearer/token"
@@ -124,6 +137,21 @@ func (p *Prometheus) Init() error {
 	if p.MetricVersion != 2 {
 		p.Log.Warnf("Use of deprecated configuration: 'metric_version = 1'; please update to 'metric_version = 2'")
 	}
+
+	if len(p.KubernetesLabelSelector) > 0 {
+		_, err := labels.Parse(p.KubernetesLabelSelector)
+		if err != nil {
+			return fmt.Errorf("label selector validation failed %q: %v", p.KubernetesLabelSelector, err)
+		}
+	}
+
+	if len(p.KubernetesFieldSelector) > 0 {
+		_, err := fields.ParseSelector(p.KubernetesFieldSelector)
+		if err != nil {
+			return fmt.Errorf("field selector validation failed %s: %v", p.KubernetesFieldSelector, err)
+		}
+	}
+
 	return nil
 }