SQL Server 2014 (12.0.4439.1) to SP2 (12.5000) service start failure
We have SSISDB installed and it's in an AG. I ran the upgrade package on the secondary and received an error 


Secondary user databases in an availability group are not available to be written to (readable at best). Thus the upgrade failed as the database is part of the AG and not able to be written to.


  How do I go about bringing this thing back up? Do I actually need to restore the master DB?


I haven't tested it but you should be able to recover using -m, remove the SSISDB from the AG, then restart as normal.

Going forward you'll want to remove the SSISDB from the AG before running the upgrade and bringing it back in after the upgrade. Is it a pain? Yep. Will it stop you from having issues? Yep.