def docker_routable_ip
      case @docker_url.scheme
      when 'tcp', 'http', 'https'
        docker_dns = @docker_url.host
        docker_port = @docker_url.port || 2376
      else
        # Cheap trick: for unix, file or other protocols, assume docker ports
        # are proxied to localhost in addition to other interfaces
        docker_dns = 'localhost'
        docker_port = 2376
      end

      addr = Addrinfo.getaddrinfo(
        docker_dns, docker_port,
        Socket::AF_INET, Socket::SOCK_STREAM).first

      addr && addr.ip_address
    end
def docker_routable_ip
      case @docker_url.scheme
      when 'tcp', 'http', 'https'
        docker_dns = @docker_url.host
        docker_port = @docker_url.port || 2376
      else
        # Cheap trick: for unix, file or other protocols, assume docker ports
        # are proxied to localhost in addition to other interfaces
        docker_dns = 'localhost'
        docker_port = 2376
      end

      addr = Addrinfo.getaddrinfo(
        docker_dns, docker_port,
        Socket::AF_INET, Socket::SOCK_STREAM).first

      addr && addr.ip_address
    end
Figure out the likely IP address of the host pointed to by
 self.docker_url.

 @return [String] host-reachable IPv4 address of docker host