Add periodic reconnection functionality (#111)

This adds a new option "AsyncReconnectInterval" that defines the
interval at which an async connection to FluentdHost is refreshed.

This option is useful when FluentdHost is backed by a service pool,
where a set of healthy Fluentd workers are managed dynamically
behind a host name.

Signed-off-by: Conor Evans <coevans@tcd.ie>
Reviewed-by: Alex Hamlin <github@alexhamlin.co>
Signed-off-by: Fujimoto Seiji <fujimoto@ceptord.net>

Author: conorevans

README.md

@@ -132,6 +132,11 @@ When Async is enabled, if this is callback is provided, it will be called on eve
 takes two arguments - a `[]byte` of the message that was to be sent and an `error`. If the `error` is not nil this means the 
 delivery of the message was unsuccessful.
 
+### AsyncReconnectInterval
+When async is enabled, this option defines the interval (ms) at which the connection
+to the fluentd-address is re-established. This option is useful if the address
+may resolve to one or more IP addresses, e.g. a Consul service address.
+
 ### SubSecondPrecision
 
 Enable time encoding as EventTime, which contains sub-second precision values. The messages encoded with this option can be received only by Fluentd v0.14 or later.

fluent/fluent.go

@@ -65,6 +65,11 @@ type Config struct {
 	AsyncConnect  bool `json:"async_connect"`
 	MarshalAsJSON bool `json:"marshal_as_json"`
 
+	// AsyncReconnectInterval defines the interval (ms) at which the connection
+	// to the fluentd-address is re-established. This option is useful if the address
+	// may resolve to one or more IP addresses, e.g. a Consul service address.
+	AsyncReconnectInterval int `json:"async_reconnect_interval"`
+
 	// Sub-second precision timestamps are only possible for those using fluentd
 	// v0.14+ and serializing their messages with msgpack.
 	SubSecondPrecision bool `json:"sub_second_precision"`
@@ -108,6 +113,9 @@ type Fluent struct {
 	closed         bool
 	wg             sync.WaitGroup
 
+	// time at which the most recent connection to fluentd-address was established.
+	latestReconnectTime time.Time
+
 	muconn sync.RWMutex
 	conn   net.Conn
 }
@@ -447,6 +455,10 @@ func (f *Fluent) connect(ctx context.Context) (err error) {
 		err = NewErrUnknownNetwork(f.Config.FluentNetwork)
 	}
 
+	if err == nil {
+		f.latestReconnectTime = time.Now()
+	}
+
 	return err
 }
 
@@ -508,6 +520,15 @@ func (f *Fluent) run(ctx context.Context) {
 				return
 			}
 
+			if f.AsyncReconnectInterval > 0 {
+				if time.Since(f.latestReconnectTime) > time.Duration(f.AsyncReconnectInterval)*time.Millisecond {
+					f.muconn.Lock()
+					f.close()
+					f.connectWithRetry(ctx)
+					f.muconn.Unlock()
+				}
+			}
+
 			err := f.writeWithRetry(ctx, entry)
 			if err != nil && err != errIsClosing {
 				fmt.Fprintf(os.Stderr, "[%s] Unable to send logs to fluentd, reconnecting...\n", time.Now().Format(time.RFC3339))

fluent/version.go

@@ -1,3 +1,3 @@
 package fluent
 
-const Version = "1.4.0"
+const Version = "1.9.0"