Every company that relies on web business should invest in web monitoring platforms. Web monitoring platforms connect to a web site and measure KPI’s such as DNS resolution time, page download time and page consistency. (Checking a specific header or content value). These synthetic transactions, that are run by the probes, help to identify server reachability.
The term “reachability” is important in here as it is not the same as “availability”. There may be some cases where your web application and it’s dependent infrastructure (Web server, DB server, Application server etc) seems to be running smoothly from your side but not the customer’s. This is usually due to routing problems on the network and problems on the remote DNS server.
It is important to know these downtime scenarios when supporting your customers. In some situations you may even take some corrective actions such as guiding users to change their DNS server settings or even opening a ticket to the remote ISP for investigation.
There are 2 important selection criteria to consider when investing in web monitoring service.
First, the service should have local probes. If your business resides in Istanbul/Turkey but your probe resides in Philadelphia/US, the response times or availability calculations may not reflect the truth. Suppose the country has a problem reaching Internet. Your probe will notify you about a downtime. However most of your local users will still be able to reach you.
Second, the service should do parallel calculations. This is for covering the load balancer scenarios. Load balancers will typically work in a round robin fashion to distribute the load across a web server farm. So, if you measure 1 time and the current web server on the queue does not have any problems, you will measure the service as “up”.
However, the next server on the pool may suffer from performance problems or even downtime. If you make at least 3 measurements at relatively same time, you would catch individual server problem within a pool. This is a very important feature you would be seeking when deciding on a web monitoring tool.
Local and parallel calculations will help you identify web server problems and troubleshoot them more quickly.