F5 performs health-checks or monitors by utilizing the status code or the content in the response from the servers to mark the server as UP or DOWN.
It is relatively easy to mark the server UP/DOWN by using a single status code in the “Receive String” attribute within the Monitor:
200 OK
If you want to mark a server up for multiple status code like using 200-209, you can use this:
HTTP/1.[01] [2]0[0-9]
In order to mark the server UP for status code 200-209 or 401
HTTP/1.[01] ([2]0[0-9]|401)
