Introduce retry mechanism for SyslogEmitter with exponential backoff

 - Add a constant for maximum retries
 - Wrap the SyslogEmitter writer with a RetryWriter to handle retries with exponential backoff
 - Update tests to expect a RetryWriter instead of a TLSWriter or TCPWriter

src/autoscaler/metricsforwarder/forwarder/syslog_emitter.go

@@ -14,6 +14,8 @@ import (
 	"code.cloudfoundry.org/loggregator-agent-release/src/pkg/egress/syslog"
 )
 
+const maxRetries int = 22
+
 type SyslogEmitter struct {
 	logger lager.Logger
 	writer egress.WriteCloser
@@ -78,8 +80,19 @@ func NewSyslogEmitter(logger lager.Logger, conf *config.Config) (MetricForwarder
 		)
 	}
 
+	retryWriter, err := syslog.NewRetryWriter(
+		binding,
+		syslog.ExponentialDuration,
+		maxRetries,
+		writer,
+	)
+
+	if err != nil {
+		return nil, err
+	}
+
 	return &SyslogEmitter{
-		writer: writer,
+		writer: retryWriter,
 		logger: logger,
 	}, nil
 }

src/autoscaler/metricsforwarder/forwarder/syslog_emitter_test.go

@@ -112,7 +112,7 @@ var _ = Describe("SyslogEmitter", func() {
 			})
 
 			It("Writer should be TLS", func() {
-				Expect(emitter.(*forwarder.SyslogEmitter).GetWriter()).To(BeAssignableToTypeOf(&syslog.TLSWriter{}))
+				Expect(emitter.(*forwarder.SyslogEmitter).GetWriter()).To(BeAssignableToTypeOf(&syslog.RetryWriter{}))
 			})
 		})
 
@@ -122,7 +122,7 @@ var _ = Describe("SyslogEmitter", func() {
 			})
 
 			It("Writer should be TCP", func() {
-				Expect(emitter.(*forwarder.SyslogEmitter).GetWriter()).To(BeAssignableToTypeOf(&syslog.TCPWriter{}))
+				Expect(emitter.(*forwarder.SyslogEmitter).GetWriter()).To(BeAssignableToTypeOf(&syslog.RetryWriter{}))
 			})
 		})
 	})