Your monitoring system has no need to integrate with nginx... It would monitor your actual systems, not nginx's ability to monitor your systems. Nginx shouldn't

Your monitoring system has no need to integrate with nginx... It would monitor your actual systems, not nginx's ability to monitor your systems. Nginx shouldn't be the first to tell you system x is down. A poor man's solution could be a bash while loop with wget and sleep, hitting the actual servers or just the nginx frontend. A better solution would be any one of the hundreds of monitoring systems you can pick from that do exactly that, and integrate with nginx. And yes, those are valid values for status codes. A tad surprising at first perhaps. Nginx exposes logs. Your monitoring system can handle those logs. A simple tail and a grep for 'Upstream server failed' in the error log would be fine. Better than manually opening some custom gui that offers the same info, just in a worse format you can't work with.