clair: better introspection server defaults

This change has the introspection server spin up on a random port if an
address is not provided, instead of the default of ":http".

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

cmd/clair/introspection.go

@@ -25,28 +25,26 @@ const (
 
 func introspection(ctx context.Context, cfg *config.Config, healthCheck func() bool) (*http.Server, error) {
 	mux := http.NewServeMux()
-	srv := http.Server{
-		Addr: cfg.IntrospectionAddr,
-	}
+	srv := http.Server{}
 	log := zerolog.Ctx(ctx).With().Logger()
 
 	// Metrics config
-	if n := cfg.Metrics.Name; n != "" {
-		log.Info().Str("sink", n).Msg("configuring metrics sink")
+	if cfg.Metrics.Name == "" {
+		cfg.Metrics.Name = "default"
 	}
+	log.Info().Str("sink", cfg.Metrics.Name).Msg("configuring metrics sink")
 	switch cfg.Metrics.Name {
-	case "":
-		log.Info().Str("sink", "default").Msg("configuring metrics sink")
-		fallthrough // will default to prometheus
+	case "default":
+		log.Info().Str("sink", "default").Msg("defaulting to prometheus")
+		fallthrough
 	case "prometheus":
-		log.Info().Str("sink", "prometheus").Msg("configuring metrics sink")
 		endpoint := "/metrics"
 		if cfg.Metrics.Prometheus.Endpoint != nil {
 			endpoint = *cfg.Metrics.Prometheus.Endpoint
 		}
 		log.Info().
-			Str("url", srv.Addr+endpoint).
-			Msg("configuring prometheus")
+			Str("endpoint", endpoint).
+			Msg("configuring prometheus on introspection server")
 		promlog := log.With().
 			Str("component", "metrics-exporter").
 			Logger()
@@ -61,7 +59,6 @@ func introspection(ctx context.Context, cfg *config.Config, healthCheck func() b
 		srv.RegisterOnShutdown(pipeline.Stop)
 		mux.HandleFunc(endpoint, hf)
 	case "dogstatsd":
-		log.Info().Str("sink", "dogstatsd").Msg("configuring metrics sink")
 		log.Info().
 			Str("endpoint", cfg.Metrics.Dogstatsd.URL).
 			Msg("configuring dogstatsd")

cmd/clair/main.go

@@ -70,20 +70,34 @@ func main() {
 
 	// Make sure to configure our metrics and tracing providers before creating
 	// any package objects that may close over a provider.
+	//
+	// This is structured in a non-idiomatic way because we don't want a failure
+	// to stop the program.
 	intro, err := introspection(ctx, &conf, func() bool { return true })
 	if err != nil {
 		logger.Error().Err(err).Msg("failed to create introspection server")
 	} else {
 		intro.BaseContext = logfunc
-		logger.Info().
-			Str("addr", intro.Addr).
-			Msgf("launching introspection via http")
-		go func() {
-			if err := intro.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-				logger.Error().Err(err).Msg("launching introspection via http failed")
-			}
-			defer intro.Shutdown(ctx)
-		}()
+		addr := conf.IntrospectionAddr
+		if addr == "" {
+			addr = ":0"
+		}
+		l, err := net.Listen("tcp", addr)
+		if err != nil {
+			l.Close()
+			logger.Error().Err(err).Msg("failed to create introspection server")
+		} else {
+			logger.Info().
+				Str("addr", l.Addr().String()).
+				Msgf("launching introspection via http")
+			// The Serve method closes the net.Listener.
+			go func() {
+				if err := intro.Serve(l); err != nil && err != http.ErrServerClosed {
+					logger.Error().Err(err).Msg("launching introspection via http failed")
+				}
+				defer intro.Shutdown(ctx)
+			}()
+		}
 	}
 
 	// return a http server with the correct handlers given the config's Mode attribute.