Add support for static and random routing keys in kafka output

plugins/outputs/kafka/README.md

@@ -50,6 +50,11 @@ This plugin writes to a [Kafka Broker](http://kafka.apache.org/07/quickstart.htm
   ##  ie, if this tag exists, its value will be used as the routing key
   routing_tag = "host"
 
+  ## Static routing key.  Used when no routing_tag is set or as a fallback
+  ## when the tag specified in routing tag is not found.  If set to "random",
+  ## a random value will be generated for each message.
+  routing_key = "random"
+
   ## CompressionCodec represents the various compression codecs recognized by
   ## Kafka in messages.
   ##  0 : No compression

plugins/outputs/kafka/kafka.go

@@ -10,6 +10,7 @@ import (
 	tlsint "github.com/influxdata/telegraf/internal/tls"
 	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	uuid "github.com/satori/go.uuid"
 
 	"github.com/Shopify/sarama"
 )
@@ -22,24 +23,16 @@ var ValidTopicSuffixMethods = []string{
 
 type (
 	Kafka struct {
-		// Kafka brokers to send metrics to
-		Brokers []string
-		// Kafka topic
-		Topic string
-		// Kafka client id
-		ClientID string `toml:"client_id"`
-		// Kafka topic suffix option
-		TopicSuffix TopicSuffix `toml:"topic_suffix"`
-		// Routing Key Tag
-		RoutingTag string `toml:"routing_tag"`
-		// Compression Codec Tag
+		Brokers          []string
+		Topic            string
+		ClientID         string      `toml:"client_id"`
+		TopicSuffix      TopicSuffix `toml:"topic_suffix"`
+		RoutingTag       string      `toml:"routing_tag"`
+		RoutingKey       string      `toml:"routing_key"`
 		CompressionCodec int
-		// RequiredAcks Tag
-		RequiredAcks int
-		// MaxRetry Tag
-		MaxRetry int
-		// Max Message Bytes
-		MaxMessageBytes int `toml:"max_message_bytes"`
+		RequiredAcks     int
+		MaxRetry         int
+		MaxMessageBytes  int `toml:"max_message_bytes"`
 
 		Version string `toml:"version"`
 
@@ -116,6 +109,11 @@ var sampleConfig = `
   ##  ie, if this tag exists, its value will be used as the routing key
   routing_tag = "host"
 
+  ## Static routing key.  Used when no routing_tag is set or as a fallback
+  ## when the tag specified in routing tag is not found.  If set to "random",
+  ## a random value will be generated for each message.
+  routing_key = "random"
+
   ## CompressionCodec represents the various compression codecs recognized by
   ## Kafka in messages.
   ##  0 : No compression
@@ -273,6 +271,22 @@ func (k *Kafka) Description() string {
 	return "Configuration for the Kafka server to send metrics to"
 }
 
+func (k *Kafka) routingKey(metric telegraf.Metric) string {
+	if k.RoutingTag != "" {
+		key, ok := metric.GetTag(k.RoutingTag)
+		if ok {
+			return key
+		}
+	}
+
+	if k.RoutingKey == "random" {
+		u := uuid.NewV4()
+		return u.String()
+	}
+
+	return k.RoutingKey
+}
+
 func (k *Kafka) Write(metrics []telegraf.Metric) error {
 	msgs := make([]*sarama.ProducerMessage, 0, len(metrics))
 	for _, metric := range metrics {
@@ -285,8 +299,9 @@ func (k *Kafka) Write(metrics []telegraf.Metric) error {
 			Topic: k.GetTopicName(metric),
 			Value: sarama.ByteEncoder(buf),
 		}
-		if h, ok := metric.GetTag(k.RoutingTag); ok {
-			m.Key = sarama.StringEncoder(h)
+		key := k.routingKey(metric)
+		if key != "" {
+			m.Key = sarama.StringEncoder(key)
 		}
 		msgs = append(msgs, m)
 	}

plugins/outputs/kafka/kafka_test.go

@@ -2,7 +2,9 @@ package kafka
 
 import (
 	"testing"
+	"time"
 
+	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/plugins/serializers"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/require"
@@ -96,3 +98,44 @@ func TestValidateTopicSuffixMethod(t *testing.T) {
 		require.NoError(t, err, "Topic suffix method used should be valid.")
 	}
 }
+
+func TestRoutingKeyStatic(t *testing.T) {
+	k := &Kafka{
+		RoutingKey: "static",
+	}
+
+	metric, err := metric.New(
+		"cpu",
+		map[string]string{},
+		map[string]interface{}{
+			"value": 42.0,
+		},
+		time.Unix(0, 0),
+	)
+	require.NoError(t, err)
+
+	expected := "static"
+	actual := k.routingKey(metric)
+	require.Equal(t, expected, actual)
+	require.NoError(t, err)
+}
+
+func TestRoutingKeyRandom(t *testing.T) {
+	k := &Kafka{
+		RoutingKey: "random",
+	}
+
+	metric, err := metric.New(
+		"cpu",
+		map[string]string{},
+		map[string]interface{}{
+			"value": 42.0,
+		},
+		time.Unix(0, 0),
+	)
+	require.NoError(t, err)
+
+	actual := k.routingKey(metric)
+	require.Equal(t, 36, len(actual))
+	require.NoError(t, err)
+}