docs: def register_instances(name, instances, region=None, key=None, keyid=None,
                         profile=None):
      '''
      Register instances with an ELB.  Instances is either a string
      instance id or a list of string instance id's.
  
      Returns:
  
      - ``True``: instance(s) registered successfully
      - ``False``: instance(s) failed to be registered
  
      CLI example:
  
      .. code-block:: bash
  
          salt myminion boto_elb.register_instances myelb instance_id
          salt myminion boto_elb.register_instances myelb "[instance_id,instance_id]"
      '''
      # convert instances to list type, enabling consistent use of instances
      # variable throughout the register_instances method
      if isinstance(instances, six.string_types) or isinstance(instances, six.text_type):
          instances = [instances]
      conn = _get_conn(region=region, key=key, keyid=keyid, profile=profile)
  
      try:
          registered_instances = conn.register_instances(name, instances)
      except boto.exception.BotoServerError as error:
          log.warning(error)
          return False
      registered_instance_ids = [instance.id for instance in
                                 registered_instances]
      # register_failues is a set that will contain any instances that were not
      # able to be registered with the given ELB
      register_failures = set(instances).difference(set(registered_instance_ids))
      if register_failures:
          log.warning('Instance(s): %s not registered with ELB %s.',
                      list(register_failures), name)
          register_result = False
      else:
          register_result = True
      return register_result