Use default partition key when tag does not exist in kinesis output (#4904)

plugins/outputs/kinesis/README.md

@@ -71,7 +71,7 @@ All metrics will be mapped to the same shard which may limit throughput.
 #### tag
 
 This will take the value of the specified tag from each metric as the paritionKey.
-If the tag is not found an empty string will be used.
+If the tag is not found the `default` value will be used or `telegraf` if unspecified
 
 #### measurement
 

plugins/outputs/kinesis/kinesis.go

@@ -36,8 +36,9 @@ type (
 	}
 
 	Partition struct {
-		Method string `toml:"method"`
-		Key    string `toml:"key"`
+		Method  string `toml:"method"`
+		Key     string `toml:"key"`
+		Default string `toml:"default"`
 	}
 )
 
@@ -90,10 +91,11 @@ var sampleConfig = `
   #    method = "measurement"
   #
   ## Use the value of a tag for all writes, if the tag is not set the empty
-  ## string will be used:
+  ## default option will be used. When no default, defaults to "telegraf"
   #  [outputs.kinesis.partition]
   #    method = "tag"
   #    key = "host"
+  #    default = "mykey"
 
 
   ## Data format to output.
@@ -187,10 +189,13 @@ func (k *KinesisOutput) getPartitionKey(metric telegraf.Metric) string {
 		case "measurement":
 			return metric.Name()
 		case "tag":
-			if metric.HasTag(k.Partition.Key) {
-				return metric.Tags()[k.Partition.Key]
+			if t, ok := metric.GetTag(k.Partition.Key); ok {
+				return t
+			} else if len(k.Partition.Default) > 0 {
+				return k.Partition.Default
 			}
-			log.Printf("E! kinesis : You have configured a Partition using tag %+v which does not exist.", k.Partition.Key)
+			// Default partition name if default is not set
+			return "telegraf"
 		default:
 			log.Printf("E! kinesis : You have configured a Partition method of %+v which is not supported", k.Partition.Method)
 		}

plugins/outputs/kinesis/kinesis_test.go

@@ -29,13 +29,22 @@ func TestPartitionKey(t *testing.T) {
 	}
 	assert.Equal(testPoint.Tags()["tag1"], k.getPartitionKey(testPoint), "PartitionKey should be value of 'tag1'")
 
+	k = KinesisOutput{
+		Partition: &Partition{
+			Method:  "tag",
+			Key:     "doesnotexist",
+			Default: "somedefault",
+		},
+	}
+	assert.Equal("somedefault", k.getPartitionKey(testPoint), "PartitionKey should use default")
+
 	k = KinesisOutput{
 		Partition: &Partition{
 			Method: "tag",
 			Key:    "doesnotexist",
 		},
 	}
-	assert.Equal("", k.getPartitionKey(testPoint), "PartitionKey should be value of ''")
+	assert.Equal("telegraf", k.getPartitionKey(testPoint), "PartitionKey should be telegraf")
 
 	k = KinesisOutput{
 		Partition: &Partition{