Testing in production

http://searchsoftwarequality.techtarget.com/answer/Release-management-Software-testing-in-production raise the question of whether it is okay to test in production. Some say "never", the author is more nuanced in his answer. So far, I've never had the chance to work in projects where the pre-production or QA environment were conform replicas to the production environment and therefor I've always seen the need to test in production.

A new vulnerability is discovered in a library on the application server or the database server or IT has to make a change in the production environment, etc. There are a large number of reasons why we not only can but must test in production. It does need to be bounded by processes and communication streams more stringent than in the development environment so that tests don't triggers alarms (DoS for exemple) or don't skew the stats but planning for test in production is a must if one does not want to have very unpleasant conversation with the CSO...