Nginx configuration in OS X

I want to server-side load balance for gRPC client and server and trying to come up with simple Nginx config for the OS X. I have 2 servers running on the port 50051 and 50052 and this is I start the server:

Server server = ServerBuilder.forPort(50051)
                .addService(new ImageStreamingServerImpl())
                .addService(ProtoReflectionService.newInstance())
//                .useTransportSecurity(
//                        new File("ssl/server.crt"),
//                        new File("ssl/server.pem")
//                )
                .build();
        
        server.start();

This is my Nginx config:

worker_processes  1;

error_log  /usr/local/var/log/nginx/error.log;

events {
    worker_connections  10;
}

http {
    access_log  /usr/local/var/log/nginx/access.log;

    upstream backend {
        server 0.0.0.0:50051;
        server 0.0.0.0:50052;
    }

    server {
        listen 8080;

        location / {
            grpc_pass grpc://backend;
        }
    }
}

So my idea is the client can listen to the port of 8080 over the Nginx and perform the code as before. Client creation is below:

  ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 8080)
                .usePlaintext()
                .build();

//        ManagedChannel channel = NettyChannelBuilder.forAddress("localhost", 8080)
//                .sslContext(GrpcSslContexts.forClient().trustManager(new File("ssl/ca.crt")).build())
//                .build();
        
        FileServiceGrpc.FileServiceStub imageStreamingClient = FileServiceGrpc.newStub(channel);

Previously, the client and server can run decently in the same port (say, 50051 or 50052) without Nginx. Why does this not working now?

The proto file is provided below:

syntax = "proto3";

option java_multiple_files = true;
package com.grpc.protobuf;

message DownloadFileRequest {
  string url = 1;
}

message DataChunk {
  bytes data = 1;
  int32 size = 2;
}

service FileService {
  rpc downloadFile (DownloadFileRequest) returns (stream DataChunk);
}

I omit the TLS encryption for the simplification purpose.

It doesn't look like you have configured Nginx to enabled HTTP2, which is the protocol used by gRPC.

Try with:

server {
   listen 8080 http2; 
   ....
}