'Registers an Amazon EBS volume with a specified stack. A
volume can be registered with only one stack at a time. If the
volume is already registered, you must first deregister it by
calling DeregisterVolume. For more information, see `Resource
Management`_.
**Required Permissions**: To use this action, an IAM user must
have a Manage permissions level for the stack, or an attached
policy that explicitly grants permissions. For more
information on user permissions, see `Managing User
Permissions`_.
:type ec_2_volume_id: string
:param ec_2_volume_id: The Amazon EBS volume ID.
:type stack_id: string
:param stack_id: The stack ID.'

def register_volume(self, stack_id, ec_2_volume_id=None):

    params = {'StackId': stack_id}
    if (ec_2_volume_id is not None):
        params['Ec2VolumeId'] = ec_2_volume_id
    return self.make_request(action='RegisterVolume', body=json.dumps(params))
