Demonstrate connecting to GKE cluster from outside, starting pod, grabbing logs

example

$ go run main.go -tok=$(gcloud auth print-access-token) -project=$(gcloud config get-value core/project)
There are 41 pods in the cluster
...
There are 3 nodes in the cluster
-> gke-cluster-1-default-pool-968a07e0-bw9p
-> gke-cluster-1-default-pool-968a07e0-gxzx
-> gke-cluster-1-default-pool-968a07e0-xrdh
Created pod foo-k4twr
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
container "noop" in pod "foo-k4twr" is waiting to start: ContainerCreating
hello
rpc error: code = Unknown desc = Error: No such container: fb338e4172d6827b4f61feab1982fa236f3faf053ddc17607c271a15d733b807
took 6.152402206s

main.go

package main

import (
	"context"
	"encoding/base64"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"strings"
	"time"

	"golang.org/x/oauth2"
	gke "google.golang.org/api/container/v1beta1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
)

var (
	projectID   = flag.String("project", "", "GCP project")
	zone        = flag.String("zone", "us-east1-b", "GCP zone")
	clusterName = flag.String("cluster", "cluster-1", "GKE cluster name")
	tok         = flag.String("tok", "", "OAuth2 token")
)

func main() {
	flag.Parse()
	ctx := context.Background()

	svc, err := gke.New(oauth2.NewClient(ctx, oauth2.StaticTokenSource(&oauth2.Token{AccessToken: *tok})))
	if err != nil {
		log.Fatalf("New service: %v", err)
	}
	cluster, err := svc.Projects.Zones.Clusters.Get(*projectID, *zone, *clusterName).Do()
	if err != nil {
		log.Fatalf("Get cluster: %v", err)
	}

	caBytes, err := base64.StdEncoding.DecodeString(cluster.MasterAuth.ClusterCaCertificate)
	if err != nil {
		log.Fatal(err)
	}
	config := &rest.Config{
		Host:            "https://" + cluster.Endpoint,
		Username:        cluster.MasterAuth.Username,
		Password:        cluster.MasterAuth.Password,
		TLSClientConfig: rest.TLSClientConfig{CAData: caBytes},
	}

	clientset, err := kubernetes.NewForConfig(config)
	if err != nil {
		log.Fatal(err)
	}

	// Get pods
	pods, err := clientset.CoreV1().Pods("").List(metav1.ListOptions{})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))

	for _, p := range pods.Items {
		fmt.Println("->", p.Namespace, p.Name)
	}

	// Get nodes
	nodes, err := clientset.CoreV1().Nodes().List(metav1.ListOptions{})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("There are %d nodes in the cluster\n", len(nodes.Items))
	for _, n := range nodes.Items {
		fmt.Println("->", n.Name)
	}

	// Start a pod
	pod, err := clientset.CoreV1().Pods("default").Create(&corev1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			GenerateName: "foo-",
		},
		Spec: corev1.PodSpec{
			Containers: []corev1.Container{{
				Name:    "noop",
				Image:   "busybox",
				Command: []string{"/bin/echo"},
				Args:    []string{"hello"},
			}},
		},
	})
	if err != nil {
		fmt.Println("error creating pod: %v", err)
	}
	fmt.Println("Created pod", pod.Name)
	podStart := time.Now()

	// Read pod logs
	req := clientset.CoreV1().RESTClient().Get().Namespace("default").Name(pod.Name).Resource("pods").SubResource("log").Param("follow", "true")
	for {
		rc, err := req.Stream()
		if err != nil {
			fmt.Println(err)
			continue
		}
		b, err := ioutil.ReadAll(rc)
		rc.Close()
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(string(b))
		if strings.Contains(string(b), "hello") {
			fmt.Println("took", time.Since(podStart))
			break
		}
	}
}