code: func (d *Driver) SetConfigFromFlags(flags drivers.DriverOptions) error {
  	d.ActiveTimeout = flags.Int("rackspace-active-timeout")
  	d.Username = flags.String("rackspace-username")
  	d.APIKey = flags.String("rackspace-api-key")
  	d.Region = flags.String("rackspace-region")
  	d.EndpointType = flags.String("rackspace-endpoint-type")
  	d.ImageId = flags.String("rackspace-image-id")
  	d.FlavorId = flags.String("rackspace-flavor-id")
  	d.SSHUser = flags.String("rackspace-ssh-user")
  	d.SSHPort = flags.Int("rackspace-ssh-port")
  	d.SetSwarmConfigFromFlags(flags)
  
  	if d.Region == "" {
  		return missingEnvOrOption("Region", "OS_REGION_NAME", "--rackspace-region")
  	}
  	if d.Username == "" {
  		return missingEnvOrOption("Username", "OS_USERNAME", "--rackspace-username")
  	}
  	if d.APIKey == "" {
  		return missingEnvOrOption("API key", "OS_API_KEY", "--rackspace-api-key")
  	}
  
  	if d.ImageId == "" {
  		// Default to the Ubuntu 16.04 image.
  		// This is done here, rather than in the option registration, to keep the default value
  		// from making "machine create --help" ugly.
  		d.ImageId = "821ba5f4-712d-4ec8-9c65-a3fa4bc500f9"
  	}
  
  	if d.EndpointType != "publicURL" && d.EndpointType != "adminURL" && d.EndpointType != "internalURL" {
  		return fmt.Errorf("invalid endpoint type %q (must be publicURL, adminURL or internalURL)", d.EndpointType)
  	}
  
  	return nil
  }
docs: // SetConfigFromFlags assigns and verifies the command-line arguments presented to the driver.