Enable profiler and profile-guided builds

I used the chance to simplify the Makefile, as this is required for the file check to work correctly. Variables should not contain quotes, as these will be included in the value otherwise.

cmd/poseidon/main.go

@@ -15,6 +15,8 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"runtime/pprof"
+	"strconv"
 	"syscall"
 	"time"
 )
@@ -22,9 +24,21 @@ import (
 var (
 	gracefulShutdownWait = 15 * time.Second
 	log                  = logging.GetLogger("main")
+	// If pgoEnabled is true, the binary was built with PGO enabled.
+	// This is set during compilation with our Makefile as a STRING.
+	pgoEnabled = "false"
 )
 
-func initSentry(options *sentry.ClientOptions) {
+func initSentry(options *sentry.ClientOptions, profilingEnabled bool) {
+	options.BeforeSendTransaction = func(event *sentry.Event, _ *sentry.EventHint) *sentry.Event {
+		if event.Tags == nil {
+			event.Tags = make(map[string]string)
+		}
+		event.Tags["go_pgo"] = pgoEnabled
+		event.Tags["go_profiling"] = strconv.FormatBool(profilingEnabled)
+		return event
+	}
+
 	if err := sentry.Init(*options); err != nil {
 		log.Errorf("sentry.Init: %s", err)
 	}
@@ -37,6 +51,33 @@ func shutdownSentry() {
 	}
 }
 
+func initProfiling(options config.Profiling) (cancel func()) {
+	if options.Enabled {
+		profile, err := os.Create(options.File)
+		if err != nil {
+			log.WithError(err).Error("Error while opening the profile file")
+		}
+
+		log.Debug("Starting CPU profiler")
+		if err := pprof.StartCPUProfile(profile); err != nil {
+			log.WithError(err).Error("Error while starting the CPU profiler!!")
+		}
+
+		cancel = func() {
+			if options.Enabled {
+				log.Debug("Stopping CPU profiler")
+				pprof.StopCPUProfile()
+				if err := profile.Close(); err != nil {
+					log.WithError(err).Error("Error while closing profile file")
+				}
+			}
+		}
+	} else {
+		cancel = func() {}
+	}
+	return cancel
+}
+
 func runServer(server *http.Server) {
 	log.WithField("address", server.Addr).Info("Starting server")
 	var err error
@@ -139,9 +180,12 @@ func main() {
 		log.WithError(err).Warn("Could not initialize configuration")
 	}
 	logging.InitializeLogging(config.Config.Logger.Level)
-	initSentry(&config.Config.Sentry)
+	initSentry(&config.Config.Sentry, config.Config.Profiling.Enabled)
 	defer shutdownSentry()
 
+	stopProfiling := initProfiling(config.Config.Profiling)
+	defer stopProfiling()
+
 	cancel := monitoring.InitializeInfluxDB(&config.Config.InfluxDB)
 	defer cancel()