I am currently developing a webapp with a gRPC backend. For this I am using gRPC-Web and the Envoy proxy between the webapp and the backend service. It is all going fine but now I wanted to deploy it to a digitalocean server and was setting up NGINX as a reverse proxy and to serve my index.html file. The following is basically my architecture with the ports of the individual services. The Envoy proxy and the gRPC backend are running in Docker containers:

My nginx.conf now looks like this:

server {
    listen 80;
    listen [::]:80;

    root /var/www/;

    index index.html index.htm;

    server_name myDomain.com

    location / {
        try_files $uri $uri /index.html?$args;
    }

    location /api {
        proxy_http_version 1.1;
        proxy_pass http://localhost:8000;
        proxy_set_header Connection "";
    }
}

Now I am getting the error

grpc-message: "unknown service api/proto.Service"
grpc-status: "12"

even if the method is implemented and it is running great locally. Any help is highly appreciated :)

EDIT: After some debugging, I am thinking that returning the answer from the service through Envoy and Nginx is the issue. For example, when I send the request while the Envoy proxy is running BUT the backend service is not running, I am getting the correct error 503 (Service Unavailable). As soon as the backend gRPC service is running again, I am reciving the unkown service api/proto.Service error.

As requested, my docker-compose.yaml file:

version: "3.9"
services:
  postgres:
    container_name: postgres
    hostname: postgres
    volumes:
      - ./management/postgres/postgres_data:/var/lib/postgresql/data
    build: ./management/postgres/
    ports: 
      - "5432:5432"
    environment:
      - POSTGRES_USER=$DB_USER
      - POSTGRES_PASSWORD=$DB_PWD
      - POSTGRES_DB=$DB_NAME

  backend:
    container_name: backend
    ports: 
      - "50051:50051"
    depends_on:
      - postgres
    build: ./service
    environment:
      - POSTGRES_PASSWORD=$DB_PWD

  envoy:
    build: ./management/proxies
    ports:
      - "8000:8000"

My envoy.yaml proxy:

admin:
  access_log_path: /tmp/admin_access.log
  address:
    socket_address: { address: 0.0.0.0, port_value: 9901 }

static_resources:
  listeners:
  - name: listener_0
    address:
      socket_address: { address: 0.0.0.0, port_value: 8000 }
    filter_chains:
    - filters:
      - name: envoy.filters.network.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          codec_type: auto
          stat_prefix: ingress_http
          route_config:
            name: local_route
            virtual_hosts:
            - name: local_service
              domains: ["*"]
              routes:
              - match: { prefix: "/" }
                route:
                  cluster: grpc_server 
                  timeout: 0s
                  max_stream_duration:
                    grpc_timeout_header_max: 0s
              cors:
                allow_origin_string_match:
                - prefix: "*"
                allow_methods: GET, PUT, DELETE, POST, OPTIONS
                allow_headers: keep-alive,user-agent,cache-control,content-type,content-transfer-encoding,custom-header-1,x-accept-content-transfer-encoding,x-accept-response-streaming,x-user-agent,x-grpc-web,grpc-timeout
                max_age: "1728000"
                expose_headers: custom-header-1,grpc-status,grpc-message
          http_filters:
          - name: envoy.filters.http.grpc_web
          - name: envoy.filters.http.cors
          - name: envoy.filters.http.router
  clusters:
  - name: grpc_server
    connect_timeout: 0.25s
    type: logical_dns
    http2_protocol_options: {}
    lb_policy: round_robin
    load_assignment:
      cluster_name: cluster_0
      endpoints:
        - lb_endpoints:
            - endpoint:
                address:
                  socket_address:
                    address: backend
                    port_value: 50051