# File lib/rds/right_rds_interface.rb, line 190
    def create_db_instance(aws_id, master_username, master_user_password, params={})
      request_hash = {}
      # Mandatory
      request_hash['DBInstanceIdentifier'] = aws_id
      request_hash['MasterUsername']       = master_username
      request_hash['MasterUserPassword']   = master_user_password
      # Mandatory with default values
      request_hash['DBInstanceClass']  = params[:instance_class].blank?    ? DEFAULT_INSTANCE_CLASS : params[:instance_class].to_s
      request_hash['AllocatedStorage'] = params[:allocated_storage].blank? ? 25            : params[:allocated_storage]
      request_hash['Engine']           = params[:engine].blank?            ? 'MySQL5.1'    : params[:engine]
      # Optional
      request_hash['EndpointPort']               = params[:endpoint_port]                unless params[:endpoint_port].blank?
      request_hash['DBName']                     = params[:db_name]                      unless params[:db_name].blank?
      request_hash['AvailabilityZone']           = params[:availability_zone]            unless params[:availability_zone].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.merge!(amazonize_list('DBSecurityGroups.member',  params[:db_security_groups]))
#      request_hash.merge!(amazonize_list('DBParameterGroups.member', params[:db_parameter_groups]))
      request_hash['DBParameterGroup']           = params[:db_parameter_group]           unless params[:db_parameter_group].blank?
      link = generate_request('CreateDBInstance', request_hash)
      request_info(link, DescribeDbInstancesParser.new(:logger => @logger))[:db_instances].first
    end