Akka streamlet utilities


Use case

An GrpcServerLogic can be used to handle gRPC requests. You need to extend your streamlet from AkkaServerStreamlet so that Cloudflow will expose an HTTP endpoint in Kubernetes.

Additionally, you need to enable HTTP/2 by adding the following to your configuration:

akka.http.server.preview.enable-http2 = on


gRPC is a contract-first technology, so you start by adding the protobuf definition for the service you want to expose to src/main/protobuf. In this example we will implement a simple request-response service:

syntax = "proto3";

option java_multiple_files = true;
option java_package = "sensordata.grpc";
option java_outer_classname = "SensorDataProto";

package sensordata;

service SensorDataService {
    rpc Provide (SensorData) returns (SensorReply) {}

message SensorData {
    string payload = 1;

message SensorReply {
    string message = 1;

Because the Akka gRPC plugin is embedded in Cloudflow, the code for the service will automatically be generated when you compile this service. In this case, a sensordata.grpc.SensorDataService will be generated that you can implement.

To expose your implementation, extend AkkaServerStreamlet and use GrpcServerLogic to add your gRPC handlers:

  override def createLogic = new GrpcServerLogic(this) {
    override def handlers() =
      List(SensorDataServiceHandler.partial(new SensorDataServiceImpl(sinkRef(out))), ServerReflection.partial(List(SensorDataService)))
    public AkkaStreamletLogic createLogic() {
        return new GrpcServerLogic(this, getContext()) {
            public List<Function<HttpRequest, CompletionStage<HttpResponse>>> handlers() {
                return List.of(
                        SensorDataServiceHandlerFactory.partial(new SensorDataServiceImpl(), SensorDataService.name, system()),
                        ServerReflection.create(List.of(SensorDataService.description), system()));

Exposing through an ingress

gRPC services use HTTP/2 as a transport mechanism. Cloudflow supports both HTTP and HTTP/2 on the port exposed by the pod.

When you want to expose your gRPC service to external clients, you will need to expose it as a HTTP/2 service to the outside. Configuring an ingress to support HTTP/2 might be possible with the correct additional configuration, but is currently not officially supported, and might even require code changes.