Today society requires services available 24×7, IT management requires knowledge of the state of the services offered. This necessity have created a lot of tools, products and services. The main approach for this is the external web monitoring.
External web monitoring approach a tries to simulate the actions done by the clients, that is if the clients visits webpages, the monitor software will simulate as a client a request to the webserver, there are some pitfalls on that approach, let’s review them:
Where is located the monitor? Is it representative of the location of clients? Could it detect WAN Network problems? Normally this is solved with monitors distributed across continents being representative of Internet world availability
-Which is the url being monitored? It is very difficult to find a always representative URL, if you simply test a static web page the monitor will miss when the database is not working, the disk is full, or the application server is failing, even is difficult for the monitor to know if the answer of the page is right or not. If the monitor detects the page is failing that is true, but there could be a lot of times that the web is failing and the monitors didn’t notice it.
The first approach:
#wget http://www.bpmalert.com/index.html
A better approach
#wget http://www.bpmalert.com/register.php?user=test&data=test
but the response from the webserver could be “200 OK” but the webpage could say “Database error”.
Even accessing a simple url doesn’t emulate today web complexities, pages are not a simple url, it have a lot of components, and there are things like cookies, session id, ajax, that are not emulated.
-Simulating user flow: As we explain if we limit the monitoring to only a url, you dind’t see the full flow of a web process, for example a real customer will register, receive a mail, click a link and then make a purchase. There are very complex tools that uses real browsers, with a recorded user session and so on, but is impossible to simulate a real user, only a real person could confirm that the web is working ok.
There are some tools that emulates user behaviour but are more used to load tests than for availability monitoring, some of these tools are:
As a conclusion the external monitoring of webservers are a necessary but they are imperfect, and must be completed with other business monitors in order to know that everything is working ok.
