Trouble using exec provider type with Lets Encrypt Go and docker

Traefik Traefik v2 (latest)
1

I am trying to use the exec provider type with the lets encrypt go in a docker container. The error I am getting is:

2019-07-25T07:18:04.711127150Z time="2019-07-25T07:18:04Z" level=error msg="Unable to obtain ACME certificate for domains \"[domain]\" : unable to generate a certificate for the domains [domain]: acme: Error -> One or more domains had a problem:\n[domain] [domain] acme: error presenting token: fork/exec \"/etc/traefik/dynu.py\": no such file or directory\n"

I have a python script (dynu.py) that works correctly on the host - I have copied the script into my ${USERFOLDER}/traefik folder on the host and re-run docker-compose. My compose yaml specifies the EXEC_PATH environment variable and the volume linking /etc/traefik in the container to the path on the host. I've copied my compose details below. Any ideas?

  traefik:
    hostname: traefik
    image: traefik:latest
    container_name: traefik
    restart: always
    domainname: ${DOMAINNAME}
    networks:
      - default
      - traefik_proxy
    ports:
      - "80:80"
      - "443:443"
      - "8080:8080"
    environment:
      - EXEC_PATH="/etc/traefik/dynu.py"
    labels:
      - "traefik.enable=true"
      - "traefik.backend=traefik"
      - "traefik.frontend.rule=Host:traefik.${DOMAINNAME}"
      - "traefik.port=8080"
      - "traefik.docker.network=traefik_proxy"
    volumes:
          - /var/run/docker.sock:/var/run/docker.sock:ro
          - ${USERDIR}/docker/traefik:/etc/traefik
          - ${USERDIR}/docker/shared:/shared
2

The Traefik docker image is based on a scratch image. There is no shell, no extras.

If you need to run a python script, you will have to build your own docker image with python.
You may be able to use the alpine image and install python there.

That is why you are getting the exec failures.