Use container vars environment in docker-compose command key

Question

I have two services in mine docker-compose.yml: docker-gen and nginx. Docker-gen is associated with nginx. For docker-gen to work, I have to pass the actual name or hash of the nginx container so that docker-gen can restart nginx when it changes.

When I bind docker-gen with nginx, a set of environment variables appears in the docker-gen container, the most interesting for me is NGINX_NAMEthe name of the nginx container.

Thus, it should be easy to put $NGINX_NAMEin the service field commandand make it work. But it $NGINX_NAMEdoes not expand when I start the services. Looking through the docker logs, I see the lines:

2015/04/24 12:54:27 Sending container '$NGINX_NAME' signal '1'
2015/04/24 12:54:27 Error sending signal to container: No such container: $NGINX_NAME

My docker_config.ymllooks like this:

nginx:
  image: nginx:latest
  ports:
    - '80:80'
  volumes:
    - /tmp/nginx:/etc/nginx/conf.d

dockergen:
  image: jwilder/docker-gen:latest
  links:
    - nginx
  volumes_from:
    - nginx
  volumes:
    - /var/run/docker.sock:/tmp/docker.sock
    - ./extra:/etc/docker-gen/templates
    - /etc/nginx/certs
  tty: true
  command: >
    -watch
    -only-exposed
    -notify-sighup "$NGINX_NAME"
    /etc/docker-gen/templates/nginx.tmpl
    /etc/nginx/conf.d/default.conf

, , ?

Answer 1

entrypoint dockergen command:

dockergen:
  image: jwilder/docker-gen:latest
  links:
    - nginx
  volumes_from:
    - nginx
  volumes:
    - /var/run/docker.sock:/tmp/docker.sock
    - ./extra:/etc/docker-gen/templates
    - /etc/nginx/certs
  tty: true
  entrypoint: ["/bin/sh", "-c"]
  command: >
    "
    docker-gen
    -watch
    -only-exposed
    -notify-sighup $(echo $NGINX_NAME | tail -c +2)
    /etc/docker-gen/templates/nginx.tmpl
    /etc/nginx/conf.d/default.conf
    "

, Docker, '/', SIGHUP , :

$ docker kill -s SIGHUP /myproject_dockergen_1/nginx

, nginx , . , $(echo $NGINX_NAME | tail -c +2) , char $NGINX_NAME.