Implementing a gRPC Service

gRPC service implementations exposed as CDI beans are automatically registered and served by quarkus-grpc.

Implementing a gRPC service requires the gRPC classes to be generated. Place your proto files in src/main/proto and run mvn compile.

Generated Code

Quarkus generates a few implementation classes for services declared in the proto file:

  1. A service interface using the Mutiny API

    • the class name is ${JAVA_PACKAGE}.${NAME_OF_THE_SERVICE}

  2. An implementation base class using the gRPC API

    • the class name is structured as follows: ${JAVA_PACKAGE}.${NAME_OF_THE_SERVICE}Grpc.${NAME_OF_THE_SERVICE}ImplBase

For example, if you use the following proto file snippet:

option java_package = "hello"; (1)

service Greeter { (2)
    rpc SayHello (HelloRequest) returns (HelloReply) {}
1 hello is the java package for the generated classes.
2 Greeter is the service name.

Then the service interface is hello.Greeter and the implementation base is the abstract static nested class: hello.GreeterGrpc.GreeterImplBase.

You’ll need to implement the service interface or extend the base class with your service implementation bean as described in the following sections.

Implementing a Service with the Mutiny API

To implement a gRPC service using the Mutiny API, create a class that implements the service interface. Then, implement the methods defined in the service interface. If you don’t want to implement a service method just throw an java.lang.UnsupportedOperationException from the method body (the exception will be automatically converted to the appropriate gRPC exception). Finally, implement the service and add the @GrpcService annotation:

import io.quarkus.grpc.GrpcService;
import hello.Greeter;

@GrpcService (1)
public class HelloService implements Greeter { (2)

    public Uni<HelloReply> sayHello(HelloRequest request) {
        return Uni.createFrom().item(() ->
                HelloReply.newBuilder().setMessage("Hello " + request.getName()).build()
1 A gRPC service implementation bean must be annotated with the @GrpcService annotation and should not declare any other CDI qualifier. All gRPC services have the javax.inject.Singleton scope. Additionally, the request context is always active during a service call.
2 hello.Greeter is the generated service interface.
The service implementation bean can also extend the Mutiny implementation base, where the class name is structured as follows: Mutiny${NAME_OF_THE_SERVICE}Grpc.${NAME_OF_THE_SERVICE}ImplBase.

Implementing a Service with the default gRPC API

To implement a gRPC service using the default gRPC API, create a class that extends the default implementation base. Then, override the methods defined in the service interface. Finally, implement the service and add the @GrpcService annotation:

import io.quarkus.grpc.GrpcService;

public class HelloService extends GreeterGrpc.GreeterImplBase {

    public void sayHello(HelloRequest request, StreamObserver<HelloReply> responseObserver) {
        String name = request.getName();
        String message = "Hello " + name;

Blocking Service Implementation

By default, all the methods from a gRPC service run on the event loop. As a consequence, you must not block. If your service logic must block, annotate the method with io.smallrye.common.annotation.Blocking:

public Uni<HelloReply> sayHelloBlocking(HelloRequest request) {
    // Do something blocking before returning the Uni

Handling Streams

gRPC allows receiving and returning streams:

service Streaming {
    rpc Source(Empty) returns (stream Item) {} // Returns a stream
    rpc Sink(stream Item) returns (Empty) {}   // Reads a stream
    rpc Pipe(stream Item) returns (stream Item) {}  // Reads a streams and return a streams

Using Mutiny, you can implement these as follows:

import io.quarkus.grpc.GrpcService;

public class StreamingService implements Streaming {

    public Multi<Item> source(Empty request) {
        // Just returns a stream emitting an item every 2ms and stopping after 10 items.
        return Multi.createFrom().ticks().every(Duration.ofMillis(2))
                .map(l -> Item.newBuilder().setValue(Long.toString(l)).build());

    public Uni<Empty> sink(Multi<Item> request) {
        // Reads the incoming streams, consume all the items.
        return request
                .map(l -> Empty.newBuilder().build());

    public Multi<Item> pipe(Multi<Item> request) {
        // Reads the incoming stream, compute a sum and return the cumulative results
        // in the outbound stream.
        return request
                .onItem().scan(() -> 0L, Long::sum)
                .onItem().transform(l -> Item.newBuilder().setValue(Long.toString(l)).build());

Health Check

For the implemented services, Quarkus gRPC exposes health information in the following format:

syntax = "proto3";


message HealthCheckRequest {
  string service = 1;

message HealthCheckResponse {
  enum ServingStatus {
    UNKNOWN = 0;
    SERVING = 1;
    NOT_SERVING = 2;
  ServingStatus status = 1;

service Health {
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse);

  rpc Watch(HealthCheckRequest) returns (stream HealthCheckResponse);

Clients can specify the fully qualified service name to get the health status of a specific service or skip specifying the service name to get the general status of the gRPC server.

For more details, check out the gRPC documentation

Additionally, if Quarkus SmallRye Health is added to the application, a readiness check for the state of the gRPC services will be added to the MicroProfile Health endpoint response, that is /q/health.

Reflection Service

Quarkus gRPC Server implements the reflection service. This service allows tools like grpcurl or grpcox to interact with your services.

The reflection service is enabled by default in dev mode. In test or production mode, you need to enable it explicitly by setting quarkus.grpc.server.enable-reflection-service to true.


By default, quarkus-grpc starts a single gRPC server running on a single event loop.

If you wish to scale your server, you can set the number of server instances by setting quarkus.grpc.server.instances.

Server Configuration

Configuration property fixed at build time - All other configuration properties are overridable at runtime

Configure the gRPC server



The gRPC Server port.



The gRPC Server port used for tests.



The gRPC server host.


The gRPC handshake timeout.


The max inbound message size in bytes.


The max inbound metadata size in bytes


The classpath path or file path to a server certificate or certificate chain in PEM format.


The classpath path or file path to the corresponding certificate private key file in PEM format.


An optional key store which holds the certificate information instead of specifying separate files. The key store can be either on classpath or an external file.


An optional parameter to specify the type of the key store file. If not given, the type is automatically detected based on the file name.


A parameter to specify the password of the key store file. If not given, the default ("password") is used.



An optional trust store which holds the certificate information of the certificates to trust The trust store can be either on classpath or an external file.


An optional parameter to specify type of the trust store file. If not given, the type is automatically detected based on the file name.


A parameter to specify the password of the trust store file.


The cipher suites to use. If none is given, a reasonable default is selected.

list of string

The list of protocols to explicitly enable.

list of string


Configures the engine to require/request client authentication. NONE, REQUEST, REQUIRED

none, request, required


Disables SSL, and uses plain text instead. If disabled, configure the ssl configuration.



Whether ALPN should be used.



The path to the certificate file.


The path to the private key file.


Enables the gRPC Reflection Service. By default, the reflection service is only exposed in dev mode. This setting allows overriding this choice and enable the reflection service every time.



Number of gRPC server verticle instances. This is useful for scaling easily across multiple cores. The number should not exceed the amount of event loops.



Sets a custom keep-alive duration. This configures the time before sending a keepalive ping when there is no read activity.


gRPC compression, e.g. "gzip"


About the Duration format

The format for durations uses the standard java.time.Duration format. You can learn more about it in the Duration#parse() javadoc.

You can also provide duration values starting with a number. In this case, if the value consists only of a number, the converter treats the value as seconds. Otherwise, PT is implicitly prepended to the value to obtain a standard java.time.Duration format.

Example of Configuration

Enabling TLS

To enable TLS, use the following configuration.

Note that all paths in the configuration may either specify a resource on the classpath (typically from src/main/resources or its subfolder) or an external file.

When SSL/TLS is configured, plain-text is automatically disabled.

TLS with Mutual Auth

To use TLS with mutual authentication, use the following configuration:


Server Interceptors

gRPC server interceptors let you perform logic, such as authentication, before your service is invoked.

You can implement a gRPC server interceptor by creating an @ApplicationScoped bean implementing io.grpc.ServerInterceptor:

// add @GlobalInterceptor for interceptors meant to be invoked for every service
public class MyInterceptor implements ServerInterceptor {

    public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> serverCall,
            Metadata metadata, ServerCallHandler<ReqT, RespT> serverCallHandler) {
        // ...
Check the ServerInterceptor JavaDoc to properly implement your interceptor.

To apply an interceptor to all exposed services, annotate it with @io.quarkus.grpc.GlobalInterceptor. To apply an interceptor to a single service, register it on the service with @io.quarkus.grpc.RegisterInterceptor:

import io.quarkus.grpc.GrpcService;
import io.quarkus.grpc.RegisterInterceptor;

public class StreamingService implements Streaming {
    // ...

When you have multiple server interceptors, you can order them by implementing the javax.enterprise.inject.spi.Prioritized interface. Please note that all the global interceptors are invoked before the service-specific interceptors.

public class MyInterceptor implements ServerInterceptor, Prioritized {

    public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> serverCall,
            Metadata metadata, ServerCallHandler<ReqT, RespT> serverCallHandler) {
        // ...

    public int getPriority() {
        return 10;

Interceptors with the highest priority are called first. The default priority, used if the interceptor does not implement the Prioritized interface, is 0.

Testing your services

The easiest way to test a gRPC service is to use a gRPC client as described in Consuming a gRPC Service.

Please note that in the case of using a client to test an exposed service that does not use TLS, there is no need to provide any configuration. E.g. to test the HelloService defined above, one could create the following test:

public class HelloServiceTest implements Greeter {

    Greeter client;

    void shouldReturnHello() {
        CompletableFuture<String> message = new CompletableFuture<>();
                .subscribe().with(reply -> message.complete(reply.getMessage()));
        assertThat(message.get(5, TimeUnit.SECONDS)).isEqualTo("Hello Quarkus");

Trying out your services manually

In the dev mode, you can try out your gRPC services in the Quarkus Dev UI. Just go to http://localhost:8080/q/dev and click on Services under the gRPC tile.

Please note that your application needs to expose the "normal" HTTP port for the Dev UI to be accessible. If your application does not expose any HTTP endpoints, you can create a dedicated profile with a dependency on quarkus-vertx-http:


Having it, you can run the dev mode with: mvn quarkus:dev -Pdevelopment.

If you use Gradle, you can simply add a dependency for the quarkusDev task:

dependencies {
    quarkusDev 'io.quarkus:quarkus-vertx-http'

gRPC Server metrics

Enabling metrics collection

gRPC server metrics are automatically enabled when the application also uses the quarkus-micrometer extension. Micrometer collects the metrics of all the gRPC services implemented by the application.

As an example, if you export the metrics to Prometheus, you will get:

# HELP grpc_server_responses_sent_messages_total The total number of responses sent
# TYPE grpc_server_responses_sent_messages_total counter
grpc_server_responses_sent_messages_total{method="SayHello",methodType="UNARY",service="helloworld.Greeter",} 6.0
# HELP grpc_server_processing_duration_seconds The total time taken for the server to complete the call
# TYPE grpc_server_processing_duration_seconds summary
grpc_server_processing_duration_seconds_count{method="SayHello",methodType="UNARY",service="helloworld.Greeter",statusCode="OK",} 6.0
grpc_server_processing_duration_seconds_sum{method="SayHello",methodType="UNARY",service="helloworld.Greeter",statusCode="OK",} 0.016216771
# HELP grpc_server_processing_duration_seconds_max The total time taken for the server to complete the call
# TYPE grpc_server_processing_duration_seconds_max gauge
grpc_server_processing_duration_seconds_max{method="SayHello",methodType="UNARY",service="helloworld.Greeter",statusCode="OK",} 0.007985236
# HELP grpc_server_requests_received_messages_total The total number of requests received
# TYPE grpc_server_requests_received_messages_total counter
grpc_server_requests_received_messages_total{method="SayHello",methodType="UNARY",service="helloworld.Greeter",} 6.0

The service name, method and type can be found in the tags.

Disabling metrics collection

To disable the gRPC server metrics when quarkus-micrometer is used, add the following property to the application configuration: