# File lib/rds/right_rds_interface.rb, line 221
    def modify_db_instance(aws_id, params={})
      request_hash = {}
      # Mandatory
      request_hash['DBInstanceIdentifier'] = aws_id
      # Optional
      request_hash['MasterUserPassword']         = params[:master_user_password]           unless params[:master_user_password].blank?
      request_hash['DBInstanceClass']            = params[:instance_class].to_s.capitalize unless params[:instance_class].blank?
      request_hash['PreferredMaintenanceWindow'] = params[:preferred_maintenance_window]   unless params[:preferred_maintenance_window].blank?
      request_hash['BackupRetentionPeriod']      = params[:backup_retention_period]        unless params[:backup_retention_period].blank?
      request_hash['PreferredBackupWindow']      = params[:preferred_backup_window]        unless params[:preferred_backup_window].blank?
      request_hash['AllocatedStorage']           = params[:allocated_storage]              unless params[:allocated_storage].blank?
      request_hash['ApplyImmediately']           = params[:apply_immediately].to_s         unless params[:apply_immediately].blank?
      request_hash.merge!(amazonize_list('DBSecurityGroups.member',  params[:db_security_groups]))
#      request_hash.merge!(amazonize_list('DBParameterGroups.member', params[:db_parameter_groups]))
      request_hash['DBParameterGroupName']       = params[:db_parameter_group]             unless params[:db_parameter_group].blank?
      link = generate_request('ModifyDBInstance', request_hash)
      request_info(link, DescribeDbInstancesParser.new(:logger => @logger))[:db_instances].first
    end