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docker-gen for Docker Cloud

This is an enhancment to the docker-gen image that adds support for Docker Cloud.

This image is used in context of this post on using JrCs/docker-letsencrypt-nginx-proxy-companion to generate Let's Encrypt certificates for a Ghost specific stack.

The problem

The usual way of using docker-gen in conjunction with docker-letsencrypt-nginx-proxy-companion using the separate container method, is as follows (as per the docs):

$ docker run -d \
    --name nginx-gen \
    --volumes-from nginx \
    -v /path/to/nginx.tmpl:/etc/docker-gen/templates/nginx.tmpl:ro \
    -v /var/run/docker.sock:/tmp/docker.sock:ro \
    jwilder/docker-gen \
    -notify-sighup nginx -watch -only-exposed -wait 5s:30s /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf

however, within a Docker Cloud based environment we cannot use -notify-sighup nginx due to the fact that the container names (on the actual nodes) do not match their Service names. The result is that the nginx container (Service) never get's reloaded to take advantage of the generated Nginx configuration.

The solution

How we get around this is to add the Docker Cloud CLI to the docker-gen image and add a script (restart_service.sh) that uses the CLI to redeploy a Service. For example, the following configuration, using Docker Cloud Stack file format, would be used to achieve the desired affect:

nginx-gen:
  image: donovanmuller/docker-gen-docker-cloud:1
  volumes:
    - "/var/run/docker.sock:/tmp/docker.sock:ro"
  volumes_from:
    - nginx-proxy
    - ghost-nginx-proxy-config
  entrypoint: /usr/local/bin/docker-gen -notify-output -notify "./restart_service.sh" -watch -only-exposed -wait 10s:30s /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf
  environment:
    - PROXY_SERVICE_ENV_VAR=nginx-proxy
  roles:
   - global

Note the use of the restart_service.sh script with -notify-output -notify "./restart_service.sh". Instead of using -notify-sighup the script is executed which uses the docker-cloud CLI to redeploy the Service indicated by the environment variable PROXY_SERVICE_ENV_VAR. This variable represents the Service name (nginx-proxy in the example above) to redeploy, not the container name.

We also need the global role so that Docker Cloud can inject the DOCKERCLOUD_AUTH details needed by docker-cloud CLI to authenticate against.