def start_wsgi_server(port, addr='', registry=REGISTRY):
    """Starts a WSGI server for prometheus metrics as a daemon thread."""
    app = make_wsgi_app(registry)
    httpd = make_server(addr, port, app, handler_class=_SilentHandler)
    t = threading.Thread(target=httpd.serve_forever)
    t.daemon = True
    t.start()