upstream nnapibackends {
        server 127.0.0.1:18090;
        server 127.0.0.1:18091;
}
server {
        listen 18088;
        server_name nnapi;
        client_max_body_size 64m;
        location / {
                proxy_pass http://nnapibackends;
                proxy_next_upstream error;
        }
        access_log /var/log/nginx/nnapi.access_log;
        error_log /var/log/nginx/nnapi.error_log;
}