Make Traefik see containers from other networks? - docker

Question

I'm trying to make Traefik notice a container that belongs to a different network. Consider the following docker-compose.yml, which is the only file in that directory:
version: '3.7'
services:
traefik:
image: "traefik:v2.1"
container_name: "traefik"
hostname: "traefik"
ports:
- "80:80"
volumes:
- "/var/run/docker.sock:/var/run/docker.sock:ro"
command:
- '--providers.docker.defaultRule=Host(`{{ index .Labels "com.docker.compose.service" }}.docker.localhost`)'
- '--providers.docker.exposedbydefault=false'
- '--entrypoints.web.address=:80'
And the following project, sitting in a directory flask:
flask/docker-compose.yml
version: '3.7'
services:
flaskapp:
container_name: flaskapp
build: flask_app
expose:
- 5000
labels:
traefik.enable: true
traefik.docker.network: traefik_default
traefik.http.routers.flaskapp.rule: Host(`flaskapp.localhost`)
traefik.http.routers.flaskapp.entrypoints: web
flask/flask_app/Dockerfile
FROM python:3.8
RUN python3.8 -m pip install flask
ADD ./main.py .
EXPOSE 5000
ENTRYPOINT ./main.py
flask/flask_app/main.py
#!/usr/bin/env python3.8
import flask
app = flask.Flask(__name__)
#app.route('/')
def main():
return "hello, world"
app.run(host='0.0.0.0')
I basically did sudo docker-compose up in both of the directories and found that flaskapp.localhost receives the connection, but then times out. So I tried sudo docker network connect traefik_default flaskapp to connect flaskapp to the traefik_default network, but this didn't seem change anything. Why doesn't sudo docker network connect traefik_default flaskapp help? Is there a way to make Traefik see containers from all networks without plugging it in to theirs?

Answer 1

It appears that one way to make Traefik able to access all docker-compose networks is to run it in --net host mode, by adding network_mode: "host" to its flags. Here's the modified docker-compose.yml:
version: '3.7'
services:
traefik:
image: "traefik:v2.1"
container_name: "traefik"
hostname: "traefik"
network_mode: "host"
ports:
- "80:80"
volumes:
- "/var/run/docker.sock:/var/run/docker.sock:ro"
command:
- '--providers.docker.defaultRule=Host(`{{ index .Labels "com.docker.compose.service" }}.docker.localhost`)'
- '--providers.docker.exposedbydefault=false'
- '--entrypoints.web.address=:80'
I don't unfortunately understand the security implications of this setup and thus can't tell if it's fit for production usage, but it seems to solve this particular problem.