traefik permissions 777 for acme.json are too open, please use 600

I did finally find the solution thanks to Cooshals kind help,

we have to ssh into the virtualbox-machine and make the file there, and then point it out right from the docker-compose.yml, in this case I did like this:

docker-machine ssh default
touch /var/acme.json
chmod 600 /var/acme.json

Then in my docker-compose:

volumes:
 - /var/:/var/acme.json

Finally in traefik.toml:

[acme]
  storage = "acme.json"

I solved this problem with a named docker volume:

docker-compose.yml (only showing the relevant parts of the file)

services:
  traefik:
    environment:
    - TRAEFIK_CERTIFICATESRESOLVERS_LE_ACME_STORAGE=/acme/acme.json
    volumes:
      - acme:/acme
volumes:
  acme:

In addition to the above answer, to automate the creation of the acme.json file and assign the required permissions, create a Dockerfile and call it in your docker.compose.yml

FROM traefik:2.2

RUN touch /acme.json \
  && chmod 600 /acme.json