func main()

in prometheus-to-sd/main.go [96:204]
85 lines of code
15 McCabe index (conditional complexity)

func main() {
	flag.Set("logtostderr", "true")
	flag.Var(&source, "source", "source(s) to watch in [component-name]:[http|https]://host:port/path?whitelisted=a,b,c&podIdLabel=d&namespaceIdLabel=e&containerNameLabel=f&metricsPrefix=prefix&authToken=token&authUsername=user&authPassword=password format. Can be specified multiple times")
	flag.Var(&dynamicSources, "dynamic-source",
		`dynamic source(s) to watch in format: "[component-name]:[http|https]://:port/path?whitelisted=metric1,metric2&podIdLabel=label1&namespaceIdLabel=label2&containerNameLabel=label3&metricsPrefix=prefix&authToken=token&authUsername=user&authPassword=password". Dynamic sources are components (on the same node) discovered dynamically using the kubernetes api.`,
	)

	defer glog.Flush()
	flag.Parse()

	if *delayedShutdownTimeout < 0 {
		signal.Ignore(syscall.SIGTERM)
	} else {
		sigTermChannel := make(chan os.Signal, 1)
		signal.Notify(sigTermChannel, syscall.SIGTERM)

		go func() {
			<-sigTermChannel
			glog.Infof("SIGTERM has been received, Waiting %s before the shutdown.", delayedShutdownTimeout.String())

			time.Sleep(*delayedShutdownTimeout)
			glog.Info("Shutting down after receiving SIGTERM.")
			os.Exit(0)
		}()
	}

	gceConf, err := config.GetGceConfig(*projectOverride, *clusterNameOverride, *clusterLocationOverride, *zoneOverride, *nodeOverride)
	if err != nil {
		glog.Fatalf("Failed to get GCE config: %v", err)
	}
	glog.Infof("GCE config: %+v", gceConf)

	sourceConfigs := getSourceConfigs(*metricsPrefix, gceConf)
	glog.Infof("Built the following source configs: %v", sourceConfigs)

	monitoredResourceLabels := parseMonitoredResourceLabels(*monitoredResourceLabels)
	if len(monitoredResourceLabels) > 0 {
		if *monitoredResourceTypePrefix == "" {
			glog.Fatalf("When 'monitored-resource-labels' is specified, 'monitored-resource-type-prefix' cannot be empty.")
		}
		glog.Infof("Monitored resource labels: %v", monitoredResourceLabels)
	}

	go func() {
		http.Handle("/metrics", promhttp.Handler())
		glog.Error(http.ListenAndServe(fmt.Sprintf("%s:%d", *listenAddress, *metricsPort), nil))
	}()

	go func() {
		glog.Error(http.ListenAndServe(fmt.Sprintf("%s:%d", *debugAddress, *debugPort), expvar.Handler()))
	}()

	var options []option.ClientOption
	if *gceTokenURL != "" {
		ts := config.NewAltTokenSource(*gceTokenURL, *gceTokenBody)
		options = append(options, option.WithTokenSource(ts))
	}

	uDomain := ""
	if *apioverride != "" {
		glog.Infof("Stackdriver API endpoint is overridden to %s", *apioverride)

		// option.WithEndpoint() only works with "host:port"
		endpoint, err := getEndpoint(*apioverride)
		if err != nil {
			glog.Fatalf("Error parsing --api-override: %s, with error: %v", *apioverride, err)
		}
		options = append(options, option.WithEndpoint(endpoint))

		// infer universe domain from Stackdriver api endpoint
		_, domain, found := strings.Cut(*apioverride, ".")
		if found {
			uDomain = strings.TrimSuffix(domain, "/")
		}
	}
	// override inferred universe domain with specified value
	if *universeDomain != "" {
		uDomain = *universeDomain
	}
	if uDomain != "" {
		glog.Infof("Universe domain is %s", uDomain)
		options = append(options, option.WithUniverseDomain(uDomain))
	}

	ctx := context.Background()
	client, err := monitoring.NewMetricClient(ctx, options...)
	if err != nil {
		glog.Fatalf("Failed to create client: %v", err)
	}
	glog.V(4).Infof("Successfully created gcm client")

	if len(sourceConfigs) == 0 {
		glog.Fatalf("No sources defined. Please specify at least one --source flag.")
	}

	if *scrapeInterval > *exportInterval {
		glog.Fatalf("--scrape-interval cannot be bigger than --export-interval")
	}

	for _, sourceConfig := range sourceConfigs {
		glog.V(4).Infof("Starting goroutine for %+v", sourceConfig)

		// Pass sourceConfig as a parameter to avoid using the last sourceConfig by all goroutines.
		go readAndPushDataToStackdriver(ctx, client, gceConf, sourceConfig, monitoredResourceLabels, *monitoredResourceTypePrefix)
	}

	// As worker goroutines work forever, block main thread as well.
	<-make(chan int)
}