code: func InitTracer() func() {
  	var opts []tracer.StartOption
  	// create a Tracer configuration
  	opts = append(opts, tracer.WithServiceName(fmt.Sprintf(
  		"%s.%s",
  		os.Getenv("EMPIRE_APPNAME"),
  		os.Getenv("EMPIRE_PROCESS"))))
  	if addr := os.Getenv("DDTRACE_ADDR"); addr != "" {
  		opts = append(opts, tracer.WithAgentAddr(addr))
  	}
  
  	// Initialize a Tracer and ensure a graceful shutdown
  	// using the `closer.Close()`
  	tracer := opentracer.New(opts...)
  
  	// set the Datadog tracer as a GlobalTracer
  	opentracing.SetGlobalTracer(tracer)
  
  	return func() {
  		// I can't find a way to flush in the new tracer API
  	}
  }
docs: // InitTracer configures a global datadog tracer.
  //
  // Env Vars:
  // * DDTRACE_ADDR - The host:port of the local trace agent server.
  // * EMPIRE_APPNAME - App name, used to construct the service name.
  // * EMPIRE_PROCESS - Process name, used to construct the service name.