# File lib/rds/rds.rb, line 82
        def create_db_instance(identifier, instance_class, allocated_storage, master_username, master_password, options={})
            params = {}
            params['DBInstanceIdentifier'] = identifier
            params['DBInstanceClass'] = instance_class
            params['AllocatedStorage'] = allocated_storage
            params['MasterUsername'] = master_username
            params['MasterUserPassword'] = master_password

            params['Engine'] = options[:engine] || "MySQL5.1"
            params['DBName'] = options[:db_name] if options[:db_name]
            params['AvailabilityZone'] = options[:availability_zone] if options[:availability_zone]
            params['PreferredMaintenanceWindow'] = options[:preferred_maintenance_window] if options[:preferred_maintenance_window]
            params['BackupRetentionPeriod'] = options[:preferred_retention_period] if options[:preferred_retention_period]
            params['PreferredBackupWindow'] = options[:preferred_backup_window] if options[:preferred_backup_window]

            @logger.info("Creating DB Instance called #{identifier}")

            link = do_request("CreateDBInstance", params, :pull_out_single=>[:create_db_instance_result, :db_instance])

        rescue Exception
            on_exception
        end