In Cloudmon DEM, the system monitors a website's availability by sending an HTTP request to the webserver and examining the status code of the response. A 200 OK response code signifies that the website is accessible. However, there are several reasons an application may be considered unreachable, including:
Inaccessibility of the website.
Response time exceeding 5000ms.
HTTP response codes of 4XX or 5XX.
Issues like an invalid URL, blocked TCP, or blocked HTTP ports.
When an application is not reachable, DEM displays an Apdex score of 0 and grades it as "unacceptable." This provides a clear indication of the application's unavailability.