Send messages in a batch in Kafka output

plugins/outputs/kafka/kafka.go

@@ -191,6 +191,7 @@ func (k *Kafka) GetTopicName(metric telegraf.Metric) string {
 	default:
 		topicName = k.Topic
 	}
+
 	return topicName
 }
 
@@ -272,21 +273,37 @@ func (k *Kafka) Description() string {
 }
 
 func (k *Kafka) Write(metrics []telegraf.Metric) error {
-	msgs := make([]*sarama.ProducerMessage, 0, len(metrics))
+	batches := make(map[string]map[string][]telegraf.Metric)
 	for _, metric := range metrics {
-		buf, err := k.serializer.Serialize(metric)
-		if err != nil {
-			return err
+		topicName := k.GetTopicName(metric)
+		if _, ok := batches[topicName]; !ok {
+			batches[topicName] = make(map[string][]telegraf.Metric)
 		}
 
-		m := &sarama.ProducerMessage{
-			Topic: k.GetTopicName(metric),
-			Value: sarama.ByteEncoder(buf),
+		key, _ := metric.GetTag(k.RoutingTag)
+		if _, ok := batches[topicName][key]; !ok {
+			batches[topicName][key] = make([]telegraf.Metric, 0)
 		}
-		if h, ok := metric.GetTag(k.RoutingTag); ok {
-			m.Key = sarama.StringEncoder(h)
+		batches[topicName][key] = append(batches[topicName][key], metric)
+	}
+
+	msgs := make([]*sarama.ProducerMessage, 0, len(metrics))
+	for topicName, v := range batches {
+		for routingKey, metrics := range v {
+
+			buf, err := k.serializer.SerializeBatch(metrics)
+			if err != nil {
+				return err
+			}
+
+			m := &sarama.ProducerMessage{
+				Topic: topicName,
+				Value: sarama.ByteEncoder(buf),
+				Key:   sarama.StringEncoder(routingKey),
+			}
+
+			msgs = append(msgs, m)
 		}
-		msgs = append(msgs, m)
 	}
 
 	err := k.producer.SendMessages(msgs)
@@ -299,7 +316,6 @@ func (k *Kafka) Write(metrics []telegraf.Metric) error {
 		}
 		return err
 	}
-
 	return nil
 }