Recently, I did regular patching of SQL Server, upgrading to SQL 2014 SP2 CU3. Normally this goes without any problems and we had tested it out in our test environments, but this time it took all reporting services offline.
What happened? We upgraded the DR server like normal, but in doing so it upgraded the SQL Reporting Services database which all of the other scale-out instances look to, taking them all offline at the same time.
Fortunately we were able to get the DR server back online and failover to it so the business could keep running, before patching the other instances in the scale-out deployment and bringing them back online.
Lesson learned: When applying CU’s to SQL, make sure that you can take an outage for all Reporting Services instances in the scale-out deployment.