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:
Dapr allows proxying all kinds of gRPC invocations, including unary and stream-based ones.
The following example is taken from the “hello world” grpc-go example. Although this example is in Go, the same concepts apply 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.
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.
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:
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", "server");
dapr run --app-id client --dapr-grpc-port 50007 -- go run main.go
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.
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"
...
The dapr.io/app-protocol: "grpc"
annotation tells Dapr to invoke the app using gRPC.
If your app uses a TLS connection, you can tell Dapr to invoke your app over TLS with the app-protocol: "grpcs"
annotation (full list here). Note that Dapr does not validate TLS certificates presented by the app.
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.
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.
When using Dapr to proxy streaming RPC calls using gRPC, you must set an additional metadata option dapr-stream
with value true
.
For example:
ctx = metadata.AppendToOutgoingContext(ctx, "dapr-app-id", "server")
ctx = metadata.AppendToOutgoingContext(ctx, "dapr-stream", "true")
Metadata headers = new Metadata();
Metadata.Key<String> jwtKey = Metadata.Key.of("dapr-app-id", "server");
Metadata.Key<String> jwtKey = Metadata.Key.of("dapr-stream", "true");
var metadata = new Metadata
{
{ "dapr-app-id", "server" },
{ "dapr-stream", "true" }
};
metadata = (('dapr-app-id', 'server'), ('dapr-stream', 'true'),)
const metadata = new grpc.Metadata();
metadata.add('dapr-app-id', 'server');
metadata.add('dapr-stream', 'true');
metadata = { 'dapr-app-id' : 'server' }
metadata = { 'dapr-stream' : 'true' }
grpc::ClientContext context;
context.AddMetadata("dapr-app-id", "server");
context.AddMetadata("dapr-stream", "true");
Currently, resiliency policies are not supported for service invocation via gRPC.
When proxying streaming gRPCs, due to their long-lived nature, resiliency policies are applied on the “initial handshake” only. As a consequence:
Watch this video on how to use Dapr’s gRPC proxying capability: