The monitoring is often conducted from several locations around the world to a specific website, or server, to detect issues related to general Internet latency, and network hop issues, and to prevent false positives caused by local or inter-connect problems.
When an error is detected monitoring services send out alerts via email, SMS, phone, SNMP trap, a pager that may include diagnostic information, such as a network traceroute, code capture of a web page's HTML file, a screenshot of a webpage, and even a video of a website failing.
Monitoring is essential to ensure that a website is available to users, downtime is minimized, and performance can be optimized.
[1] Monitoring can cover many things that an application needs to function, like network connectivity, Domain Name System records, database connectivity, bandwidth, and computer resources like free RAM, CPU load, disk space, events, etc.
Measuring a website's availability and reliability under various amounts of traffic is often referred to as load testing.
[2] Website monitoring can be used to hold web hosting providers accountable for their service-level agreements.
A website monitoring service can check other internet protocols besides HTTP pages and HTTPS such as FTP, SMTP, POP3, ActiveSync, IMAP, DNS, SSH, Telnet, SSL, TCP, PING, UDP, SOAP, Domain Name Expiry, SSL Certificate Expiry and a range of ports.
Typically, most website monitoring services test a server, or application, between a once-per-hour per once-per-minute.