Software Architect's Handbook

Calculating availability based on request success rate

If your software is globally distributed, perhaps by taking advantage of cloud services provided by companies such as Amazon, Microsoft, or Google, you may be experiencing very high availability, such that at least some traffic is being served at any given time. As a result, calculating availability based on time as we did previously may not be very meaningful.

An alternate calculation would be to base availability on the request success rate. This can be calculated as follows:

Your software system will have a variety of requests, some of which are more important than others, but looking ...