Just have an endpoint in your API (like /health) that doesn’t do anything but return “ok”.

So if your database goes down, your filesystem is full, etc, that endpoint will always return “ok” with HTTP 200. That way you can setup a ping monitoring service that will trigger an alarm if the process itself is down.

You of course need more pinging for the database server etc. But at least you know which service is down instead of “the whole website is down and we don’t know which parts”.