Global 404 handler

Traefik Traefik v2 (latest)
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Back again to this topic, cause I realized that the solution I described in the previous post is sub-optimal. Indeed, that was just a redirection but not a proper handling of not found errors. To improve that, the solution is attaching the ErrorPage middleware to the low-priority catchall router (Yes, I was wrong, you can definitely do that!).

Ok, let's recap:

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In a nutshell: we are gonna define a low-priority catchall router rule that kicks in only if other routers for defined services can’t handle the request. Then, such an unknown request is handled by the ErrorPage middleware that tells Nginx to serve the error page.

This is how it works:

docker-compose.yml 
version: '3.7'

services:
  # A cool reverse-proxy / load balancer
  traefik:
    # The official v2 Traefik docker image
    image: traefik:v2.2.7
    container_name: traefik
    security_opt:
      - no-new-privileges:true
    restart: always
    volumes:
      # So that Traefik can listen to the Docker events
      - /var/run/docker.sock:/var/run/docker.sock:ro
    ports:
      # http
      - 80:80
    command:
      ###########################################
      #   Static Configuration harnessing CLI   #
      ###########################################
      # Activate dashboard.
      - --api.dashboard=true

      # Enable Docker backend with default settings.
      - --providers.docker=true
      # Do not expose containers by default.
      - --providers.docker.exposedbydefault=false
      # Default Docker network used.
      - --providers.docker.network=proxy

      # --entrypoints.<name>.address for ports
      # 80 (i.e., name = webinsercure)
      - --entrypoints.webinsecure.address=:80

    networks:
      # This is the network over which Traefik communicates with other containers.
      - proxy

    labels:
      ################################################
      #   Dynamic configuration with Docker Labels   #
      ################################################
      # You can tell Traefik to consider (or not) this container by setting traefik.enable to true or false.
      # We need it for the dashboard
      traefik.enable: true

      # Dashboard
      traefik.http.routers.traefik.rule: Host(`traefik.localhost`)
      traefik.http.routers.traefik.service: api@internal
      traefik.http.routers.traefik.entrypoints: webinsecure


  # The error pages server
  nginxError:
    image: nginx:latest
    volumes:
      - ./error-pages:/usr/share/nginx/error-pages # error pages
      - ./nginx/default.conf:/etc/nginx/conf.d/default.conf # default configuration
    networks:
      # This is the network over which Traefik communicates with other containers.
      - proxy
    labels:
      traefik.enable: true

      traefik.http.routers.error-router.rule: HostRegexp(`{host:.+}`)
      traefik.http.routers.error-router.priority: 1
      traefik.http.routers.error-router.entrypoints: webinsecure
      traefik.http.routers.error-router.middlewares: error-pages-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

      traefik.http.services.error-pages-service.loadbalancer.server.port: 80


  # A defined service
  my-test-app:
    image: containous/whoami
    networks:
      # This is the network over which Traefik communicates with other containers.
      - proxy
    labels:
      traefik.enable: true
      traefik.http.routers.my-test-app.rule: Host(`test.localhost`)
      traefik.http.routers.my-test-app.entrypoints: webinsecure
      traefik.http.services.my-test-app.loadbalancer.server.port: 80


networks:
  proxy:
    external: true

You need also to confiugure Nginx to serve error pages

default.conf 
server {
    listen       80;
    server_name  localhost;

    error_page  404    /404.html;
    # other error pages here:
    # error_page  403    /403.html;

    location / {
        root  /usr/share/nginx/error-pages;
        internal;
    }
}

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