This incident was caused by Microsoft changing their domains before the announced date. Therefore, this incident was not handled as a Schoolyear service incident. Nevertheless, it is valuable to reflect and share our findings formally in this way.
Incident Summary
Last Wednesday, September 30, starting 7:28 AM UTC, our support team received a report from a customer about students getting stuck on a white screen while trying to access their exam with Schoolyear AVD enabled. All students participating in the exam were unable to enter the AVD session, facing a blank screen. An internal test and log check informed that likely all AVD exams were impacted.
The Schoolyear application uses a URL whitelist to make sure students only have access to their Azure Virtual Desktop session. A white, empty screen can occur when the Schoolyear application is redirected to a URL that is not on this whitelist. In this case, Microsoft changed the URLs for the Azure Virtual Desktop sessions before the announced date. Since the URLs were not on the whitelist yet, it resulted in blank, empty screens.
At 08:10 UTC, the Schoolyear development team patched all ongoing exams, adding the new URLs to the whitelist. The patch was instant, meaning restarts or new sessions could continue exams.
At 8:30 UTC, the Schoolyear development team implemented a fix to automatically add the URLs to the whitelists, for any exams planned in the future.
Fault
Schoolyear AVD-enabled exams, require granular URL whitelisting to prevent communication between students and the use of unauthorized materials during exams. This requires careful consideration, testing and maintenance of the whitelist after it is published by Microsoft.
While Microsoft announced the URL change, they implemented the changes earlier than announced. Since we had not updated the URLs yet, the whitelist did not contain the URLs that were needed for the changes.
Reflection
We have to be prepared for Microsoft pushing changes before the announced dates. Preparing the changes on our side as soon as possible.