Dapr’s gRPC Interface

Use the Dapr gRPC API in your application

Dapr and gRPC

Dapr implements both an HTTP and a gRPC API for local calls. gRPC is useful for low-latency, high performance scenarios and has language integration using the proto clients.

You can find a list of auto-generated clients here.

The Dapr runtime implements a proto service that apps can communicate with via gRPC.

In addition to calling Dapr via gRPC, Dapr can communicate with an application via gRPC. To do that, the app needs to host a gRPC server and implements the Dapr appcallback service

Configuring Dapr to communicate with an app via gRPC

Self hosted

When running in self hosted mode, use the --app-protocol flag to tell Dapr to use gRPC to talk to the app:

dapr run --app-protocol grpc --app-port 5005 node app.js

This tells Dapr to communicate with your app via gRPC over port 5005.

Kubernetes

On Kubernetes, set the following annotations in your deployment YAML:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
  namespace: default
  labels:
    app: myapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
      annotations:
        dapr.io/enabled: "true"
        dapr.io/app-id: "myapp"
        dapr.io/app-protocol: "grpc"
        dapr.io/app-port: "5005"
...

Invoking Dapr with gRPC - Go example

The following steps show you how to create a Dapr client and call the SaveStateData operation on it:

Import the package

package main
import (
    "context"
    "log"
    "os"
    dapr "github.com/dapr/go-sdk/client"
)

Create the client

// just for this demo
ctx := context.Background()
data := []byte("ping")
// create the client
client, err := dapr.NewClient()
if err != nil {
  logger.Panic(err)
}
defer client.Close()

Invoke the Save State method

// save state with the key key1
err = client.SaveStateData(ctx, "statestore", "key1", "1", data)
if err != nil {
  logger.Panic(err)
}
logger.Println("data saved")

Hooray!

Now you can explore all the different methods on the Dapr client.

Creating a gRPC app with Dapr

The following steps will show you how to create an app that exposes a server for Dapr to communicate with.

Import the package

package main
import (
    "context"
    "fmt"
    "log"
    "net"
    "github.com/golang/protobuf/ptypes/any"
    "github.com/golang/protobuf/ptypes/empty"
    commonv1pb "github.com/dapr/go-sdk/dapr/proto/common/v1"
    pb "github.com/dapr/go-sdk/dapr/proto/runtime/v1"
    "google.golang.org/grpc"
)

Implement the interface

// server is our user app
type server struct {
}
// EchoMethod is a simple demo method to invoke
func (s *server) EchoMethod() string {
    return "pong"
}
// This method gets invoked when a remote service has called the app through Dapr
// The payload carries a Method to identify the method, a set of metadata properties and an optional payload
func (s *server) OnInvoke(ctx context.Context, in *commonv1pb.InvokeRequest) (*commonv1pb.InvokeResponse, error) {
    var response string
    switch in.Method {
    case "EchoMethod":
        response = s.EchoMethod()
    }
    return &commonv1pb.InvokeResponse{
        ContentType: "text/plain; charset=UTF-8",
        Data:        &any.Any{Value: []byte(response)},
    }, nil
}
// Dapr will call this method to get the list of topics the app wants to subscribe to. In this example, we are telling Dapr
// To subscribe to a topic named TopicA
func (s *server) ListTopicSubscriptions(ctx context.Context, in *empty.Empty) (*pb.ListTopicSubscriptionsResponse, error) {
    return &pb.ListTopicSubscriptionsResponse{
        Subscriptions: []*pb.TopicSubscription{
            {Topic: "TopicA"},
        },
    }, nil
}
// Dapr will call this method to get the list of bindings the app will get invoked by. In this example, we are telling Dapr
// To invoke our app with a binding named storage
func (s *server) ListInputBindings(ctx context.Context, in *empty.Empty) (*pb.ListInputBindingsResponse, error) {
    return &pb.ListInputBindingsResponse{
        Bindings: []string{"storage"},
    }, nil
}
// This method gets invoked every time a new event is fired from a registerd binding. The message carries the binding name, a payload and optional metadata
func (s *server) OnBindingEvent(ctx context.Context, in *pb.BindingEventRequest) (*pb.BindingEventResponse, error) {
    fmt.Println("Invoked from binding")
    return &pb.BindingEventResponse{}, nil
}
// This method is fired whenever a message has been published to a topic that has been subscribed. Dapr sends published messages in a CloudEvents 0.3 envelope.
func (s *server) OnTopicEvent(ctx context.Context, in *pb.TopicEventRequest) (*empty.Empty, error) {
    fmt.Println("Topic message arrived")
    return &empty.Empty{}, nil
}

Create the server

func main() {
    // create listener
    lis, err := net.Listen("tcp", ":50001")
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }
    // create grpc server
    s := grpc.NewServer()
    pb.RegisterAppCallbackServer(s, &server{})
    fmt.Println("Client starting...")
    // and start...
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

This creates a gRPC server for your app on port 4000.

Run your app

To run locally, use the Dapr CLI:

dapr run --app-id goapp --app-port 4000 --app-protocol grpc go run main.go

On Kubernetes, set the required dapr.io/app-protocol: "grpc" and dapr.io/app-port: "4000 annotations in your pod spec template as mentioned above.

Other languages

You can use Dapr with any language supported by Protobuf, and not just with the currently available generated SDKs. Using the protoc tool you can generate the Dapr clients for other languages like Ruby, C++, Rust and others.

gRPC