Setting Traefik to intercept traffic between Docker containers

Question

I have Traefik container (traefik v. 2.8) running as reverse proxy for local development. I also use docker-compose.yml file to define my services.

Also, I have exposed the services present in docker-compose.yml via host.docker.internal by setting these lines in my /etc/hosts file:

127.0.0.1       host.docker.internal
localhost       host.docker.internal

My setup is as such:

host.docker.internal:8443 used for service_a
host.docker.internal:8453 used for service_b

I have setup Traefik route from a.localhost that goes to host.docker.internal:8443. I can access a.localhost from the host outside the containers just fine, and Traefik does really route the traffic to host.docker.internal:8443 as I want.

Problem is that I have a reason to have service B (host.docker.internal:8453) call service A via the a.localhost hostname. This does not work, as in service B, I get unknown host when trying to access a.localhost

Here is extract from my docker-compose.yml file:

version: '3'
services:
  reverse_proxy:
  image: traefik:v2.8
    # Enables the web UI and tells Traefik to listen to docker
    command: --api.insecure=true --providers.docker
    ports:
      - "80:80"
      - "443:443"
      # The Web UI (enabled by --api.insecure=true)
      - "9000:8080"
    volumes:
      # So that Traefik can listen to the Docker events
      - /var/run/docker.sock:/var/run/docker.sock
      - ./dev-traefik/traefik.yml:/etc/traefik/traefik.yml
      - ./dev-traefik:/configurations
  
  service_a:
    ports:
      - "8443:8443"

  service_b:
    ports:
      - "8453:8453"

Also I'm using a yml-based configuration for Traefik, present in dynamic-config.yml:

http:
  routers:
    service-a-router:
      service: service-a
      rule: "Host(`a.localhost`)"
      tls: "true" # using tls
  services:
    service-a:
      loadBalancer:
        servers:
          - url: "https://host.docker.internal:8443" # service A

tls:
  certificates:
    - certFile: "/etc/https/tls.crt"
      keyFile: "/etc/https/tls.key"
  stores:
    default:
      defaultCertificate:
        certFile: "/etc/https/tls.crt"
        keyFile: "/etc/https/tls.key"

It seems like Traefik is able to listen to requests made from host network, as accessing https://a.localhost from browser outside the container network works just fine. On the other hand, requests made by service_a container don't seem to be caught by Traefik.

What I have also tried is to add a.localhost to /etc/hosts in the host machine running the containers like this:

127.0.0.1   a.localhost
localhost   a.localhost

And then using curl inside service B container to access service A.

This resulted in getting connection refused as opposed to Could not resolve host: a.localhost. This leads me to suggest that traefik couldn't intercept traffic from service b container

What am I doing wrong? Is there a way to make such setup work? I do have a legit reason for it, which relates to having as close setup as possible in local development as on other environments which are deployed to cloud.

Setting Traefik to intercept traffic between Docker containers

0 Answers