Traefik custom error middleware for HTTP status 502 doesn't work

Traefik Traefik v2
,
1

I would like to serve custom error pages for common HTTP error codes. I was following this tutorial. For this purpose, I created the following docker-compose.yml file to test the functionality. It consists of:

  1. errorPageHandler which is a nginx server which is able to return static HTML pages (404.html and 502.html).

  2. whoami1 which routes the request to port 80 of traefik/whoami image

  3. whoami2 which routes the request to non-existent port 81 of traefik/whoami image which results in 502 - Bad Gateway

version: "3.7"

services:
  errorPageHandler:
    image: "nginx:latest"
    networks:
      - traefik-net
    volumes:
      - "./ErrorPages:/usr/share/nginx/ErrorPages"
      - "./default.conf:/etc/nginx/conf.d/default.conf"
    deploy:
      replicas: 1
      labels:
        # enable Traefik for this service
        - "traefik.enable=true"
        - "traefik.docker.network=traefik-net"

        # router (catches all requests with lowest possible priority)
        - "traefik.http.routers.error-router.rule=HostRegexp(`{catchall:.*}`)"
        - "traefik.http.routers.error-router.priority=1"
        - "traefik.http.routers.error-router.middlewares=error-pages-middleware"

        # middleware
        - "traefik.http.middlewares.error-pages-middleware.errors.status=400-599"
        - "traefik.http.middlewares.error-pages-middleware.errors.service=error-pages-service"
        - "traefik.http.middlewares.error-pages-middleware.errors.query=/{status}.html"

        # service
        - "traefik.http.services.error-pages-service.loadbalancer.server.port=80"
  
  whoami1:
    image: "traefik/whoami"
    networks:
      - traefik-net
    deploy:
      replicas: 1
      labels:
        # enable Traefik for this service
        - "traefik.enable=true"
        - "traefik.docker.network=traefik-net"

        # router
        - "traefik.http.routers.whoami1.rule=HostRegexp(`whoami1.local`)"
        - "traefik.http.routers.whoami1.service=whoami1"
        
        # service
        - "traefik.http.services.whoami1.loadbalancer.server.port=80"
        - "traefik.http.services.whoami1.loadbalancer.server.scheme=http"
        
  whoami2:
    image: "traefik/whoami"
    networks:
      - traefik-net
    deploy:
      replicas: 1
      labels:
        # enable Traefik for this service
        - "traefik.enable=true"
        - "traefik.docker.network=traefik-net"

        # router
        - "traefik.http.routers.whoami2.rule=HostRegexp(`whoami2.local`)"
        - "traefik.http.routers.whoami2.service=whoami2"
        
        # service
        - "traefik.http.services.whoami2.loadbalancer.server.port=81" # purposely wrong port
        - "traefik.http.services.whoami2.loadbalancer.server.scheme=http"

networks:
  traefik-net:
    external: true
    name: traefik-net

Folder ErrorPages contains two static HTML files, 404.html and 502.html. Content of default.conf is:

server {
    listen       80;
    server_name  localhost;

    error_page  404    /404.html;
    error_page  502    /502.html;

    location / {
        root  /usr/share/nginx/ErrorPages;
        internal;
    }
}

I added the following entries to my hosts file (172.15.16.17 is IP of the server where Traefik and all of the mentioned services are deployed) :

172.15.16.17 error404.local
172.15.16.17 whoami1.local
172.15.16.17 whoami2.local

My observations:

  1. When I visit http://error404.local, Traefik routes the request to nginx and 404.html is returned. This is expected behavior because http://error404.local doesn't match any of the routes defined in Traefik.

  2. When I visit http://whoami1.local, Traefik routes request to whoami1 service and information about container is displayed on the page (expected behavior).

  3. When I visit http://whoami2.local, Traefik doesn't route request to nginx service, but it displays its default Bad Gateway page. Why doesn't it route the request to the nginx?