# File lib/rds/rds.rb, line 89
    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