How do I implement proper Flask server that contains Server-Sent-Event API?

Solution

resp = Response(
        send_event(),
        mimetype='text/event-stream'
    )
resp.headers['X-Accel-Buffering'] = 'no'
resp.headers['Cache-Control'] = 'no-cache'
return resp

 location '/' {
        proxy_buffering off;
        proxy_cache off;
        proxy_read_timeout 12h;
        ...
        proxy_pass {your_route};
    }

/{path_to}/gunicorn --workers {num_workers} --timeout 0 --bind {path} -m 007 {module}:{app_name}