# Grpc-web middleware CORS headers

**URL:** <https://community.traefik.io/t/grpc-web-middleware-cors-headers/24346>\
**Category:** Traefik v3 (latest)\
**Tags:** docker, middleware\
**Created:** [September 7, 2024, 11:11am UTC](https://community.traefik.io/t/grpc-web-middleware-cors-headers/24346 "2024-09-07T11:11:33Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![scorpion-HF](https://sea2.discourse-cdn.com/flex020/user_avatar/community.traefik.io/scorpion-hf/32/9285_2.png) [@scorpion-HF](https://community.traefik.io/u/scorpion-HF)\
**Post date:** [September 7, 2024, 11:11am UTC](https://community.traefik.io/t/grpc-web-middleware-cors-headers/24346/1 "2024-09-07T11:11:33Z")

</div>

Hi everybody  
I just heard about the support for Grpc-web in treafik v3, so I tried to test it  
I have a python backend service which works with web blazor web client using envoy as reverse proxy but when I use treafik, I'm getting 405 Method not allowed error for OPTIONS preflight request on client side  
this is my docker-compose.yaml :

```auto
version: '3'
services:
  envoy-proxy:
    image: aibe-grpc-envoy-proxy:latest
    build:
      context: ./
      dockerfile: Dockerfile_envoy

    container_name: envoy-proxy
# network_mode: host

    depends_on:
      - grpc-server
    ports:
    - "7070:7070" # The port Envoy will listen on
    - "9901:9901" # Envoy admin port (optional)

  reverse-proxy:
    image: traefik:v3.1
    container_name: traefik
    ports:
      - "80:80" # Web traffic
      - "8080:8080" # The port Envoy will listen on
    command:
      - "--api.insecure=true"
      - "--providers.docker=true"
      - "--entrypoints.web.address=:80"
      - "--entrypoints.grpc.address=:5000"
      - "--log.level=DEBUG"
      - "--accesslog=true"
      - "--accesslog.filePath=/logs/access.log"
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"

  grpc-server:
    image: aibe-grpc-server:latest
    build:
      context: ./
      dockerfile: Dockerfile_server
    container_name: grpc-server

    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.grpc-server.rule=Host(`grpc.localhost`)"
      - "traefik.http.services.grpc-server.loadbalancer.server.port=9090"
      - "traefik.http.routers.grpc-server.entrypoints=grpc"
      - "traefik.http.services.grpc-server.loadbalancer.server.scheme=h2c"
      - "traefik.http.middlewares.grpc-middleware.grpcweb.allowOrigins=*"
      - "traefik.http.routers.grpc-server.middlewares=grpc-middleware"

```

As you can see, I also have envoy proxy and it works but my treafik container gives error; I saw that the response of OPTIONS request has header [Allow: GET, HEAD] but envoy response to OPTIONS request has more different headers [access-control-allow-origin: [http://localhost:5000](http://localhost:5000)  
access-control-allow-methods: GET, PUT, DELETE, POST, OPTIONS  
access-control-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, X-Requested-With, grpc-accept-encoding, Authorization  
access-control-max-age: 1728000  
access-control-expose-headers: custom-header-1,grpc-status,grpc-message  
date: Sat, 07 Sep 2024 10:42:38 GMT  
server: envoy  
content-length: 0]  
Can anybody help me how to solve this problem to make my treafik docker container work with my grpc web client?