That depends on how you set up and do your monitoring. Not every failure needs to be indicated by an HTTP status code. For example, on a server I'm working on

That depends on how you set up and do your monitoring. Not every failure needs to be indicated by an HTTP status code. For example, on a server I'm working on there are helper functions that generate different types of responses. Responding in certain ways will produce a 200, but will also log a warning or error. On the client side, you can create request helpers that all requests go through and that can resolve requests appropriately, rendering error messages to the user etc. The main thing is to have a well defined, consistent approach.