    # File lib/fog/aws/requests/rds/describe_db_instances.rb, line 15
            def describe_db_instances(identifier=nil, opts={})
              params = {}
              params['DBInstanceIdentifier'] = identifier if identifier
              if opts[:marker]
                params['Marker'] = opts[:marker]
              end
              if opts[:max_records]
                params['MaxRecords'] = opts[:max_records]
              end

              request({
                'Action'  => 'DescribeDBInstances',
                :parser   => Fog::Parsers::AWS::RDS::DescribeDBInstances.new
              }.merge(params))
            end