if ($app_port = 0) {
    return 502;
}

proxy_pass http://127.0.0.1:$app_port;
proxy_http_version 1.1;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;

proxy_connect_timeout 3s;
proxy_send_timeout 3600s;
proxy_read_timeout 3600s;

proxy_intercept_errors on;