Monitoring is the process of testing that end-users can interact with a website or application. It is often used by businesses and webmasters to ensure that the website or app is live and responding, making it critical to end-user experience.

There are numerous tools that can help to monitor the state of website and application, with testing of various elements:

  • web and email servers
  • security protocols
  • TCP ports
  • the integrity of web page content
  • HTTP password protection

The impact of downtime

If it’s up… A.K.A… It’s down… per year
90% n/a 876 hours
95% n/a 438 hours
99% two 9s 87 hours, 36 minutes
99.9% three 9s 8 hours, 45 minutes, 36 seconds
99.99% four 9s 52 minutes, 33.6 seconds
99.999% five 9s 5 minutes, 15.36 seconds
99.9999% six 9s 31.68 seconds

Source: Wikipedia