traefik sample for route to an external URL - add a blog.mondomain.com route to http://blog:4000

docker-compose-traefik-route-to-url.yml

traefik:
    image: traefik:v2.1.6
    container_name: traefik
    volumes:
      - "traefik.enable=true"
      - /var/run/docker.sock:/var/run/docker.sock:ro
      - ./traefik-conf.yml:/etc/traefik/traefik.yml
      - ./traefik-services.yml:/etc/traefik/services.yml
    labels:
      - "traefik.http.routers.blog.entrypoints=web_main"
      - "traefik.http.routers.blog.rule=HostRegexp(`{subdomain:blog}.{domain:moncomain.com}`)"
      - "traefik.http.routers.blog.service=blog@file"
    networks:
      - default
    expose:
      # web_main entrypoints
      - 80
    ports:
      - 80:80

traefik-conf.yml

# NOTE : conf in this file are not cumulative and cancel any option passed to traefik at launch with command in docker compose file

api:
  dashboard: true
  debug: false
  insecure: true

log:
  level: "DEBUG"


entryPoints:
  web_main:
    address: ":80"

providers:
  docker:
    endpoint: unix:///var/run/docker.sock
    # If set to false, containers that don't have a traefik.enable=true label will be ignored from the resulting routing configuration
    exposedByDefault: false
  file:
    filename: /etc/traefik/services.yml

traefik-services.yml

http:
  services:
    blog:
      loadBalancer:
        servers:
        - url: "http://blog:4000/"