Make sending server httpstartstopevents configurable

#159

Switching off these events reduces the CPU load on gorouter and
doppler VMS significantly.

These events are of type "timer".

config/config.go

@@ -275,6 +275,8 @@ type Config struct {
 	HTMLErrorTemplateFile string `yaml:"html_error_template_file,omitempty"`
 
 	PerRequestMetricsReporting bool `yaml:"per_request_metrics_reporting,omitempty"`
+
+	SendHttpStartStopServerEvent bool `yaml:"send_http_start_stop_server_event,omitempty"`
 }
 
 var defaultConfig = Config{
@@ -330,6 +332,8 @@ var defaultConfig = Config{
 	StickySessionCookieNames: StringSet{"JSESSIONID": struct{}{}},
 
 	PerRequestMetricsReporting: true,
+
+	SendHttpStartStopServerEvent: true,
 }
 
 func DefaultConfig() (*Config, error) {

config/config_test.go

@@ -628,6 +628,17 @@ backends:
 			Expect(config.PerRequestMetricsReporting).To(BeFalse())
 		})
 
+		It("defaults SendHttpStartStopServerEvent to true", func() {
+			Expect(config.SendHttpStartStopServerEvent).To(Equal(true))
+		})
+
+		It("sets SendHttpStartStopServerEvent", func() {
+			var b = []byte(`send_http_start_stop_server_event: false`)
+			err := config.Initialize(b)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(config.SendHttpStartStopServerEvent).To(BeFalse())
+		})
+
 	})
 
 	Describe("Process", func() {

proxy/proxy.go

@@ -164,7 +164,9 @@ func NewProxy(
 	n.Use(handlers.NewRequestInfo())
 	n.Use(handlers.NewProxyWriter(logger))
 	n.Use(handlers.NewVcapRequestIdHeader(logger))
-	n.Use(handlers.NewHTTPStartStop(dropsonde.DefaultEmitter, logger))
+	if cfg.SendHttpStartStopServerEvent {
+		n.Use(handlers.NewHTTPStartStop(dropsonde.DefaultEmitter, logger))
+	}
 	n.Use(handlers.NewAccessLog(accessLogger, headersToLog, logger))
 	n.Use(handlers.NewReporter(reporter, logger))
 	n.Use(handlers.NewHTTPRewriteHandler(cfg.HTTPRewrite, headersToAlwaysRemove))