separate hello and authenticate functions, force connection close at end of write cycle so we don't hold open idle connections, which has the benefit of mostly removing the chance of getting hopelessly connection lost

plugins/outputs/instrumental/instrumental.go

@@ -28,8 +28,9 @@ type Instrumental struct {
 }
 
 const (
-	DefaultHost = "collector.instrumentalapp.com"
+	DefaultHost     = "collector.instrumentalapp.com"
-	AuthFormat  = "hello version go/telegraf/1.0\nauthenticate %s\n"
+	HelloMessage    = "hello version go/telegraf/1.0\n"
+	AuthFormat      = "authenticate %s\n"
 )
 
 var (
@@ -52,6 +53,13 @@ var sampleConfig = `
 
 func (i *Instrumental) Connect() error {
 	connection, err := net.DialTimeout("tcp", i.Host+":8000", i.Timeout.Duration)
+
+	if err != nil {
+		i.conn = nil
+		return err
+	}
+
+	err = i.hello(connection)
 	if err != nil {
 		i.conn = nil
 		return err
@@ -151,6 +159,11 @@ func (i *Instrumental) Write(metrics []telegraf.Metric) error {
 		return err
 	}
 
+	// force the connection closed after sending data
+	// to deal with various disconnection scenarios and eschew holding
+	// open idle connections en masse
+	i.Close()
+
 	return nil
 }
 
@@ -162,19 +175,39 @@ func (i *Instrumental) SampleConfig() string {
 	return sampleConfig
 }
 
+func (i *Instrumental) hello(conn net.Conn) error {
+	_, err := fmt.Fprintf(conn, HelloMessage)
+	if err != nil {
+		return err
+	}
+
+	response := make([]byte, 512)
+	if _, err = conn.Read(response); err != nil {
+		fmt.Println("hello err", err)
+		return err
+	}
+
+	if string(response)[:3] != "ok\n" {
+		return fmt.Errorf("Hello failed: %s", response)
+	}
+
+	return nil
+}
+
 func (i *Instrumental) authenticate(conn net.Conn) error {
 	_, err := fmt.Fprintf(conn, AuthFormat, i.ApiToken)
 	if err != nil {
 		return err
 	}
 
-	// The response here will either be two "ok"s or an error message.
+	// The response here will either be an "ok" or an error message.
 	responses := make([]byte, 512)
 	if _, err = conn.Read(responses); err != nil {
+		fmt.Println("err was not nil: ", err)
 		return err
 	}
 
-	if string(responses)[:6] != "ok\nok\n" {
+	if string(responses)[:3] != "ok\n" {
 		return fmt.Errorf("Authentication failed: %s", responses)
 	}