How to Access Kubernetes API Server

$ kubectl exec -n default devnetools -- env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=devnetools
KUBERNETES_PORT=tcp://172.20.0.1:443
KUBERNETES_PORT_443_TCP=tcp://172.20.0.1:443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_ADDR=172.20.0.1
KUBERNETES_SERVICE_HOST=172.20.0.1
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_PORT_HTTPS=443

$ kubectl cp -n default $(which kubectl) devnetools:tmp

$ kubectl exec -n default -it devnetools -- /tmp/kubectl cluster-info

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
Error from server (Forbidden): services is forbidden: User "system:serviceaccount:default:default" cannot list resource "services" in API group "" in the namespace "kube-
system"
command terminated with exit code 1

$ kubectl create clusterrolebinding default:default:view --clusterrole=view --serviceaccount=default:default
clusterrolebinding.rbac.authorization.k8s.io/default:default:view created

$ kubectl exec -n default -it devnetools -- /tmp/kubectl cluster-info
Kubernetes master is running at https://172.20.0.1:443
CoreDNS is running at https://172.20.0.1:443/api/v1/namespaces/kube-system/services/coredns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

$ kubectl delete clusterrolebindings.rbac.authorization.k8s.io default:default:view
clusterrolebinding.rbac.authorization.k8s.io "default:default:view" deleted

$ mkdir -p github.com/samples/gocli

$ cd github.com/samples/gocli/

$ go mod init github.com/samples/gocli
go: creating new go.mod: module github.com/samples/gocli

$ cat > main.go <<EOF
package main

import (
    "context"
    "flag"
    "fmt"
    "os"
    "path/filepath"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/rest"
    "k8s.io/client-go/tools/clientcmd"
    "k8s.io/client-go/util/homedir"
    "k8s.io/klog/v2"
)

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

    // try to create the in-cluster config
    config, err := rest.InClusterConfig()
    if err != nil {
        // use the current context in kubeconfig
        config, err = clientcmd.BuildConfigFromFlags("", *kubeconfig)
        if err != nil {
            klog.Error(err)
            os.Exit(1)
        }
    }

    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        klog.Error(err)
        os.Exit(1)
    }

    pods, err := clientset.CoreV1().Pods("").List(context.TODO(), metav1.ListOptions{})
    if err != nil {
        klog.Error(err)
        os.Exit(1)
    }
    fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
}
EOF

$ go mod tidy
go: finding module for package k8s.io/client-go/kubernetes
go: downloading k8s.io/client-go v0.23.1
go: finding module for package k8s.io/client-go/rest
go: finding module for package k8s.io/client-go/tools/clientcmd
go: finding module for package k8s.io/client-go/util/homedir
go: finding module for package k8s.io/klog/v2
go: downloading k8s.io/klog/v2 v2.40.1
...

$ go build

$ ./gocli
There are 138 pods in the cluster