k8s: don't exit if not running in a kubernetes cluster

discovery/k8s.go

@@ -1,6 +1,7 @@
 package discovery
 
 import (
+	"errors"
 	"sync"
 
 	corev1 "k8s.io/api/core/v1"
@@ -9,6 +10,7 @@ import (
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/cache"
+	"k8s.io/klog"
 )
 
 type PodEventType int
@@ -41,6 +43,10 @@ type K8S struct {
 func NewK8S() (*K8S, error) {
 	config, err := rest.InClusterConfig()
 	if err != nil {
+		if errors.Is(err, rest.ErrNotInCluster) {
+			klog.Infoln("not running inside a kubernetes cluster")
+			return nil, nil
+		}
 		return nil, err
 	}
 
@@ -59,6 +65,9 @@ func NewK8S() (*K8S, error) {
 }
 
 func (k8s *K8S) Start() {
+	if len(k8s.subscribers) == 0 {
+		return
+	}
 	go k8s.start()
 }
 

main.go

@@ -37,11 +37,6 @@ func main() {
 		klog.Exitln(err)
 	}
 
-	k8s, err := discovery.NewK8S()
-	if err != nil {
-		klog.Exitln(err)
-	}
-
 	ms, err := metrics.NewMetrics()
 	if err != nil {
 		klog.Exitln(err)
@@ -51,20 +46,26 @@ func main() {
 		router.Handle("/metrics", ms.HttpHandler())
 	}
 
-	ps, err := profiles.NewProfiles()
+	cu.Start()
+	defer cu.Stop()
+
+	k8s, err := discovery.NewK8S()
 	if err != nil {
 		klog.Exitln(err)
 	}
-	if ps != nil {
-		k8s.Subscribe(ps)
-		ps.Start()
-	}
 
-	cu.Start()
-	defer cu.Stop()
-
-	k8s.Start()
-	defer k8s.Stop()
+	if k8s != nil {
+		ps, err := profiles.NewProfiles()
+		if err != nil {
+			klog.Exitln(err)
+		}
+		if ps != nil {
+			k8s.Subscribe(ps)
+			ps.Start()
+		}
+		k8s.Start()
+		defer k8s.Stop()
+	}
 
 	klog.Infoln("listening on", *flags.ListenAddress)
 	klog.Exitln(http.ListenAndServe(*flags.ListenAddress, router))