Besides these basic items, many Web sites have a variety of other important components that are vital to the health of the site. Focused monitors, by comparison, indicate precisely when a given component is in trouble. In practice, a combination of holistic and focused monitors provides the most effective and understandable picture of a Web site's current state. This can be done manually, using a browser to retrieve the page, or automatically, using a monitoring tool. A successful retrieval is an indication that many of the critical components discussed previously in Section III are functioning properly.
Failures can occur for a number of reasons, some easier to diagnose than others.
If the retrieval was done from a client located remotely on the Internet, any of the Internet links or routers between the client and the server may have been congested or broken. Narrowing down the problem space is critical because there are some classes of problems over which a Web Administrator has no control. Using a series of more focused monitors in conjunction with the holistic monitors gives overlapping coverage and allows quicker diagnosis of problems. The following are examples of common focused monitors. Ping Monitor - tests whether a machine is reachable over the network, and whether the target machine is functioning well enough to send a simple reply.