https://github.com/traefik/traefik/issues/5833

docker-compose.yml

version: '3'
services:
  dockersockwatcher:
    build: .
    tty: true
    stdin_open: true

    # WORKING
    volumes:
      - "/var/run:/var/run:ro"

    # NOT WORKING
    #volumes:
    #  - "/var/run/docker.sock:/var/run/docker.sock:ro"

docker-sock-info

GET /info HTTP/1.1
Host: localhost

Dockerfile

FROM ubuntu

RUN apt-get update && apt-get install -y netcat-openbsd

COPY ./docker-sock-info /

COPY ./watcher.sh /
RUN chmod +x /watcher.sh

CMD /watcher.sh

watcher.sh

#/bin/bash
watch "nc -q 0 -U /var/run/docker.sock < docker-sock-info"