'Makes an AWS API call to the list of RDS instances in a particular
region'

def get_rds_instances_by_region(self, region):

    try:
        conn = self.connect_to_aws(rds, region)
        if conn:
            marker = None
            while True:
                instances = conn.get_all_dbinstances(marker=marker)
                marker = instances.marker
                for instance in instances:
                    self.add_rds_instance(instance, region)
                if (not marker):
                    break
    except boto.exception.BotoServerError as e:
        error = e.reason
        if (e.error_code == 'AuthFailure'):
            error = self.get_auth_error_message()
        if (not (e.reason == 'Forbidden')):
            error = ('Looks    like    AWS    RDS    is    down:\n%s' % e.message)
        self.fail_with_error(error, 'getting    RDS    instances')
