gRPC

gRPC is a high-performance communication protocol based on HTTP/2 and protocol buffers. Its main benefits over using HTTP with JSON are:

• Protocol buffers are binary, high-performance serialization mechanism. Depending on implementation, it can be 8x faster and message size can be around 60% - 80% smaller
• Contract between service and client is explicit (by using proto files)

gRPC implementation in e-shop

In this current implementation, the communication between API Gateway and microservices leverages the usage of gRPC. gRPC is language agnostic: all services are defined using proto files. These files are based on the protobuffer language and can be found in the shared library grpc under libs/grpc/src/main/proto. Here is an example of a proto file:

syntax = "proto3";

package eshop.userService.grpc;

option java_multiple_files = true;
option java_package = "eshop.userService.grpc";
option java_outer_classname = "UserServiceProto";

service UserService {
  rpc getUserById(GetUserByIdRequest) returns (User) {}
}

message User {
  string id = 1;
  string email = 2;
  string username = 3;
}

message GetUserByIdRequest {
  string productId = 1;
}

Creating gRPC server

Each microservice is a gRPC server, which leverages grpc-server-spring-boot-starter to setup a gRPC server. In order to implement the endpoint, you need to annotate the service with GRPCService and implements the interface, which was auto-generated by the starter. Here's an example of a gRPC server in this application

@GrpcService
@RequiredArgsConstructor
public class InventoryServiceProtoServiceImpl extends InventoryServiceGrpc.InventoryServiceImplBase {

    @Override
    public void getInventoryByProductId(GetInventoryByProductIdRequest request,
                                        StreamObserver<Inventory> responseObserver) {
            // Your application code...
    }
}

Creating gRPC client

gRPC is language agnostic, though gRPC servers are implemented with Java, the clients can be implemented by any other programming language. In this case, the client is written in API gateway with Javascript/Node.js. This project uses Buf to auto generate typescript types from proto definition files. It ensures that the client is fully type-safe.