Website monitoring is a process of supervision over the performance of the site. Usually it is used to keep an eye on commercial sites or other pages for which high availability is very important.

Companies, which provide website monitoring services, let their clients to check a website, a server, port or other available from the Internet entity. The responses are collected and analyzed. Usually, the monitoring is performed from different locations, distributed over the whole world or the specific continent or country. Such monitoring is called distributed monitoringand helps to detect network-related issues as well as site or server-related. Also, distributed monitoring often makes possible to analyze the site performance from the places which are close to the real customers, instead of some distant locations which could have high latencies. The collected information could be found in a different form: email reports, graphs and different smart dependencies, to help the client to get a comprehensive view of the site's performance. Parameters like load time, speed and others can help to optimize the site performance. In case of critical error, monitoring services use variety of notification methods to deliver the alert to the client: SMS, voice call, instant messengers, email and others. This, together with immediate diagnostics, helps responsible persons like server administrators or developers to fix the site as soon as possible and minimize the duration of the failure.

Why is this important? For commercial sites, working time is proportional to their income. Roughly speaking, 2 hours of failure per day means that 1/12 part of the potential clients are lost. Even more - loyal customers also can find a more reliable competitor in case they can not receive their services/goods when they want. For other types of sites, like government, educational, NGO this is very important too. If people can't find the information fast, they'll find another source. Some parameters like site speed are important for search engines, others - database connectivity, for example - can greatly affect the convenience of usage of the site. Monitoring of some internal values like CPU load, memory consumption and disk space are important for administrators in order to prevent performance degradation. Another important purpose is verification of SLA (service-level agreement) of hosting provider. For technical issues, no site can be available 100% of time during long enough period. Sometimes servers are rebooted, updated or upgraded. So each hosting provider guarantee some specific value, which is called uptime, that shows how long can a site be down for technical reasons. Uptime is usually measured in percent. In this table it is shown for how long a site could be down for each uptime value:

• 90%          876 hours
• 95%          438 hours
• 99%          87,5 hours
• 99.9%       8 hours 45 minutes
• 99.99%     52,5 minutes
• 99.999%   5 minutes 15 seconds

If the real site performance does not correspond to SLA, it could be a reason for claim and refund request. Also, it can help the customers to select the best hosting for their needs.

Monitoring companies often provide some additional services, like vulnerability check, virus scanning, domain and certificate expiration check and many others, in order to make a useful product for their customers.

Different ways to monitor

The monitoring, based on the purpose, can be performed in several ways. Internal monitoring tools require some software to be installed into the monitored system, for example, corporate network. It helps to detect network issues, system performance and exclude or catch hardware and performance issues. External monitoring is performed from outside. It's purpose is check the availability and performance of the system by the third-party's eyes. Real user monitoring is external monitoring which simulates the real visitor of a site. Depending on complexity, such monitoring can analyze the page loading, content, sometimes - even design problems. Most advanced monitoring can offer its client to create a scenario for a visitor. This is called transaction monitoring and can perform some steps one-by-one: like load the page, navigate through menu, make a purchase. Passive monitoring is performed by a code which is integrated into the website code and sends specific information to the collector server each time the page is loaded. It helps to analyze customers actions on the site and analyze the traffic.

Monitoring services usually support different check protocols, and can monitor not only the websites, but also other entities like a file servers, mail servers, specific ports etc. Depending on task, monitoring interval can vary from several seconds to once per day.