# File lib/fog/aws/requests/rds/promote_read_replica.rb, line 36
        def promote_read_replica(identifier, backup_retention_period = nil, preferred_backup_window = nil)
          server = self.data[:servers][identifier]
          server || raise(Fog::AWS::RDS::NotFound.new("DBInstance #{identifier} not found"))

          if server["ReadReplicaSourceDBInstanceIdentifier"].nil?
            raise(Fog::AWS::RDS::Error.new("InvalidDBInstanceState => DB Instance is not a read replica."))
          end

          self.data[:modify_time] = Time.now

          data = {
            'BackupRetentionPeriod' => backup_retention_period || 1,
            'PreferredBackupWindow' => preferred_backup_window || '08:00-08:30',
            'DBInstanceIdentifier'  => identifier,
            'DBInstanceStatus'      => "modifying",
            'PendingModifiedValues' => {
              'ReadReplicaSourceDBInstanceIdentifier' => nil,
            }
          }

          server.merge!(data)

          response = Excon::Response.new
          response.body = {
            "ResponseMetadata"         => { "RequestId"  => Fog::AWS::Mock.request_id },
            "PromoteReadReplicaResult" => { "DBInstance" => server }
          }
          response.status = 200
          response
        end