How-To: Invoke services using gRPC

How-To: Invoke services using gRPC

Call between services using service invocation

This article describe how to use Dapr to connect services using gRPC. By using Dapr’s gRPC proxying capability, you can use your existing proto based gRPC services and have the traffic go through the Dapr sidecar. Doing so yields the following Dapr service invocation benefits to developers:

Mutual authentication
Tracing
Metrics
Access lists
Network level resiliency
API token based authentication

Step 1: Run a gRPC server

The following example is taken from the hello world grpc-go example.

Note this example is in Go, but applies to all programming languages supported by gRPC.

package main
import (
    "context"
    "log"
    "net"
    "google.golang.org/grpc"
    pb "google.golang.org/grpc/examples/helloworld/helloworld"
)
const (
    port = ":50051"
)
// server is used to implement helloworld.GreeterServer.
type server struct {
    pb.UnimplementedGreeterServer
}
// SayHello implements helloworld.GreeterServer
func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
    log.Printf("Received: %v", in.GetName())
    return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
}
func main() {
    lis, err := net.Listen("tcp", port)
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }
    s := grpc.NewServer()
    pb.RegisterGreeterServer(s, &server{})
    log.Printf("server listening at %v", lis.Addr())
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

This Go app implements the Greeter proto service and exposes a SayHello method.

Run the gRPC server using the Dapr CLI

dapr run --app-id server --app-port 50051 -- go run main.go

Using the Dapr CLI, we’re assigning a unique id to the app, server, using the --app-id flag.

Step 2: Invoke the service

The following example shows you how to discover the Greeter service using Dapr from a gRPC client. Notice that instead of invoking the target service directly at port 50051, the client is invoking its local Dapr sidecar over port 50007 which then provides all the capabilities of service invocation including service discovery, tracing, mTLS and retries.

package main
import (
    "context"
    "log"
    "time"
    "google.golang.org/grpc"
    pb "google.golang.org/grpc/examples/helloworld/helloworld"
    "google.golang.org/grpc/metadata"
)
const (
    address = "localhost:50007"
)
func main() {
    // Set up a connection to the server.
    conn, err := grpc.Dial(address, grpc.WithInsecure(), grpc.WithBlock())
    if err != nil {
        log.Fatalf("did not connect: %v", err)
    }
    defer conn.Close()
    c := pb.NewGreeterClient(conn)
    ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
    defer cancel()
    ctx = metadata.AppendToOutgoingContext(ctx, "dapr-app-id", "server")
    r, err := c.SayHello(ctx, &pb.HelloRequest{Name: "Darth Tyrannus"})
    if err != nil {
        log.Fatalf("could not greet: %v", err)
    }
    log.Printf("Greeting: %s", r.GetMessage())
}

The following line tells Dapr to discover and invoke an app named server:

ctx = metadata.AppendToOutgoingContext(ctx, "dapr-app-id", "server")

All languages supported by gRPC allow for adding metadata. Here are a few examples:

Java
Dotnet
Python
JavaScript
Ruby
C++

Metadata headers = new Metadata();
Metadata.Key<String> jwtKey = Metadata.Key.of("dapr-app-id", "server");
GreeterService.ServiceBlockingStub stub = GreeterService.newBlockingStub(channel);
stub = MetadataUtils.attachHeaders(stub, header);
stub.SayHello(new HelloRequest() { Name = "Darth Malak" });

var metadata = new Metadata
{
    { "dapr-app-id", "server" }
};
var call = client.SayHello(new HelloRequest { Name = "Darth Nihilus" }, metadata);

metadata = (('dapr-app-id', 'server'),)
response = stub.SayHello(request={ name: 'Darth Revan' }, metadata=metadata)

const metadata = new grpc.Metadata();
metadata.add('dapr-app-id', 'server');
client.sayHello({ name: "Darth Malgus" }, metadata)

metadata = { 'dapr-app-id' : 'server' }
response = service.sayHello({ 'name': 'Darth Bane' }, metadata)

grpc::ClientContext context;
context.AddMetadata("dapr-app-id", "Darth Sidious");

Run the client using the Dapr CLI

dapr run --app-id client --dapr-grpc-port 50007 -- go run main.go

View telemetry

If you’re running Dapr locally with Zipkin installed, open the browser at http://localhost:9411 and view the traces between the client and server.

Deploying to Kubernetes

Set the following Dapr annotations on your deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: grpc-app
  namespace: default
  labels:
    app: grpc-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: grpc-app
  template:
    metadata:
      labels:
        app: grpc-app
      annotations:
        dapr.io/enabled: "true"
        dapr.io/app-id: "server"
        dapr.io/app-protocol: "grpc"
        dapr.io/app-port: "50051"
...

If your app uses an SSL connection, you can tell Dapr to invoke your app over an insecure SSL connection with the app-ssl: "true" annotation (full list here)

The dapr.io/app-protocol: "grpc" annotation tells Dapr to invoke the app using gRPC.

Namespaces

When running on namespace supported platforms, you include the namespace of the target app in the app ID: myApp.production

For example, invoking the gRPC server on a different namespace:

ctx = metadata.AppendToOutgoingContext(ctx, "dapr-app-id", "server.production")

See the Cross namespace API spec for more information on namespaces.

Step 3: View traces and logs

The example above showed you how to directly invoke a different service running locally or in Kubernetes. Dapr outputs metrics, tracing and logging information allowing you to visualize a call graph between services, log errors and optionally log the payload body.

For more information on tracing and logs see the observability article.