client side load balancing

build/deploy/greet.svc.yaml

@@ -13,4 +13,4 @@ spec:
       targetPort: 50051
   selector:
     run: greetserver
-  type: ClusterIP
+  clusterIP: None

build/deploy/greetclient-deploy.yaml

@@ -18,8 +18,6 @@ spec:
           ports:
             - containerPort: 9091
           env:
-            - name: GRPC_SERVER_HOST
-              value: greetserver.default.svc.cluster.local
             - name: GRPC_SVC
               value: greetserver
             - name: POD_NAMESPACE

internal/app/greetclient/app.go

@@ -8,6 +8,7 @@ import (
 	"os"
 
 	"github.com/gin-gonic/gin"
+	"github.com/hiteshrepo/grpc-loadbalancing/internal/pkg/kubernetes"
 	"github.com/hiteshrepo/grpc-loadbalancing/internal/pkg/proto"
 	"google.golang.org/grpc"
 )
@@ -53,20 +54,27 @@ func (a *App) setupGreetClient() error {
 	serverHost := "localhost"
 	serverPort := "50051"
 
-	if host, ok := os.LookupEnv("GRPC_SERVER_HOST"); ok {
-		serverHost = host
-	}
-
 	if port, ok := os.LookupEnv("GRPC_SERVER_PORT"); ok {
 		serverPort = port
 	}
 
+	client, err := kubernetes.GetClusterClient()
+	if err != nil {
+		fmt.Printf("error while creating client: %s\n", err.Error())
+	}
+
+	if host := kubernetes.GetServiceDnsName(client, os.Getenv("GRPC_SVC"), os.Getenv("POD_NAMESPACE")); len(host) > 0 {
+		serverHost = host
+	}
+
 	servAddr := fmt.Sprintf("%s:%s", serverHost, serverPort)
 
 	fmt.Println("dialing", servAddr)
 
 	a.conn, err = grpc.Dial(
 		servAddr,
+		grpc.WithDefaultServiceConfig(`{"loadBalancingPolicy":"round_robin"}`),
+		grpc.WithBlock(),
 		opts,
 	)
 	if err != nil {

internal/pkg/kubernetes/client.go

@@ -0,0 +1,50 @@
+package kubernetes
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
+)
+
+const DefaultKubeConfigPath = "/home/hitesh/.kube/config"
+
+func GetClusterClient() (*kubernetes.Clientset, error) {
+	kubeconfig := flag.String("kubeconfig", "/home/hitesh/.kube/config", "location of your kubeconfig file")
+	config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
+	if err != nil {
+		log.Printf("error while building config from kubeconfig file location : %s\n", err.Error())
+		log.Println("fetching config within cluster")
+		config, err = rest.InClusterConfig()
+		if err != nil {
+			fmt.Printf("error while getting inclusterconfig : %s\n", err.Error())
+			return nil, fmt.Errorf("error while creating clusterconfig : %s", err.Error())
+		}
+	}
+
+	return kubernetes.NewForConfig(config)
+}
+
+func GetServiceDnsName(clientset *kubernetes.Clientset, serviceName, namespace string) string {
+	service, err := clientset.CoreV1().Services(namespace).Get(context.Background(), serviceName, metav1.GetOptions{})
+	if err != nil {
+		panic(err.Error())
+	}
+	var hostname string
+	if len(service.Status.LoadBalancer.Ingress) > 0 {
+		hostname = service.Status.LoadBalancer.Ingress[0].Hostname
+	} else {
+		fmt.Printf("Service %s in namespace %s has no external IP address or hostname\n", serviceName, namespace)
+	}
+
+	if hostname == "" {
+		hostname = service.Name + "." + service.Namespace + ".svc.cluster.local"
+	}
+
+	return fmt.Sprintf("dns:///%s", hostname)
+}