Recently, an Azure production application I was monitoring was experiencing a problem with stale/old data showing up intermittently as users navigated the website. I began to suspect a single instance of the application did not have a properly updated cache on it. I needed to know which Web Role Instance was causing the problem so I could restart it. Obviously, there was a bug that would need to be tracked down in the future, but the immediate need was to stop the problem.
For lack of other information, I had to restart each instance of the web role individually, waiting for that one to come back up and move on to the next. I couldn’t trust the situation until every single instance was restarted.