I am working on a dynamic kubernetes informer to watch over my kubernetes cluster for events and the discovery of all kubernetes components.

But, When I am trying to access the KUBECONFIG via the InClusterConfig method, I am getting the following error:

// go run main.go
FATA[0000] could not get config                          error="unable to load in-cluster configuration, KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT must be defined"
exit status 1

I found various similar issues related to this on kubernetes repo on github as well as stackoverflow but couldn't find any solution or workaround. [kubernetes issue, kubernetes issue, stackoverflow similar question, stackoverflow similar question]

Following is the go code and go.mod file

Go Code:

package main

import (
	"os"
	"os/signal"

	"github.com/sirupsen/logrus"
	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/dynamic"
	"k8s.io/client-go/dynamic/dynamicinformer"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/tools/clientcmd"
)

func main() {
	cfg, err := restConfig()
	if err != nil {
		logrus.WithError(err).Fatal("could not get config")
	}

	// Grab a dynamic interface that we can create informers from
	dc, err := dynamic.NewForConfig(cfg)
	if err != nil {
		logrus.WithError(err).Fatal("could not generate dynamic client for config")
	}

	// Create a factory object that we can say "hey, I need to watch this resource"
	// and it will give us back an informer for it
	f := dynamicinformer.NewFilteredDynamicSharedInformerFactory(dc, 0, v1.NamespaceAll, nil)

	// Retrieve a "GroupVersionResource" type that we need when generating our informer from our dynamic factory
	gvr, _ := schema.ParseResourceArg("deployments.v1.apps")

	// Finally, create our informer for deployments!
	i := f.ForResource(*gvr)

	stopCh := make(chan struct{})
	go startWatching(stopCh, i.Informer())

	sigCh := make(chan os.Signal, 0)
	signal.Notify(sigCh, os.Kill, os.Interrupt)

	<-sigCh
	close(stopCh)
}

func restConfig() (*rest.Config, error) {
	kubeCfg, err := rest.InClusterConfig()
	if kubeconfig := os.Getenv("KUBECONFIG"); kubeconfig != "" {
		kubeCfg, err = clientcmd.BuildConfigFromFlags("", kubeconfig)
	}

	// var kubeCfg *string
	// if home := homedir.HomeDir(); home != "" {
	// 	kubeCfg = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
	// } else {
	// 	kubeCfg = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
	// }
	// flag.Parse()

	// kubeCfg, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)

	//testing-ends

	if err != nil {
		return nil, err
	}

	return kubeCfg, nil
}

func startWatching(stopCh <-chan struct{}, s cache.SharedIndexInformer) {
	handlers := cache.ResourceEventHandlerFuncs{
		AddFunc: func(obj interface{}) {
			u := obj.(*unstructured.Unstructured)

			logrus.WithFields(logrus.Fields{
				"name":      u.GetName(),
				"namespace": u.GetNamespace(),
				"labels":    u.GetLabels(),
			}).Info("received add event!")
		},
		UpdateFunc: func(oldObj, obj interface{}) {
			logrus.Info("received update event!")
		},
		DeleteFunc: func(obj interface{}) {
			logrus.Info("received update event!")
		},
	}

	s.AddEventHandler(handlers)
	s.Run(stopCh)
}

go.mod file:

module discovery-test

go 1.15

require (
	github.com/googleapis/gnostic v0.5.3 // indirect
	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 // indirect
	github.com/imdario/mergo v0.3.11 // indirect
	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
	github.com/sirupsen/logrus v1.7.0
	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 // indirect
	golang.org/x/net v0.0.0-20201029055024-942e2f445f3c // indirect
	golang.org/x/oauth2 v0.0.0-20200902213428-5d25da1a8d43 // indirect
	golang.org/x/time v0.0.0-20200630173020-3af7569d3a1e // indirect
	k8s.io/apimachinery v0.17.0
	k8s.io/client-go v0.17.0
	k8s.io/klog v1.0.0 // indirect
	k8s.io/utils v0.0.0-20201027101359-01387209bb0d // indirect
)