'Returns information about provisioned RDS instances. This API
supports pagination.
:type db_instance_identifier: string
:param db_instance_identifier:
The user-supplied instance identifier. If this parameter is specified,
information from only the specific DB instance is returned. This
parameter isn\'t case sensitive.
Constraints:
+ Must contain from 1 to 63 alphanumeric characters or hyphens
+ First character must be a letter
+ Cannot end with a hyphen or contain two consecutive hyphens
:type filters: list
:param filters:
:type max_records: integer
:param max_records: The maximum number of records to include in the
response. If more records exist than the specified `MaxRecords`
value, a pagination token called a marker is included in the
response so that the remaining results may be retrieved.
Default: 100
Constraints: minimum 20, maximum 100
:type marker: string
:param marker: An optional pagination token provided by a previous
DescribeDBInstances request. If this parameter is specified, the
response includes only records beyond the marker, up to the value
specified by `MaxRecords` .'

def describe_db_instances(self, db_instance_identifier=None, filters=None, max_records=None, marker=None):

    params = {}
    if (db_instance_identifier is not None):
        params['DBInstanceIdentifier'] = db_instance_identifier
    if (filters is not None):
        self.build_complex_list_params(params, filters, 'Filters.member', ('FilterName', 'FilterValue'))
    if (max_records is not None):
        params['MaxRecords'] = max_records
    if (marker is not None):
        params['Marker'] = marker
    return self._make_request(action='DescribeDBInstances', verb='POST', path='/', params=params)
