A recent installer change incidentally made it so we can no longer pass in an empty osImage when generating MachineSets for Azure. Per thread we're going to try gleaning that info from the ProviderSpec of an(y ) existing worker MachineSet, similar to how we grab the AMID from a master for AWS. A failure here – including not finding any existing workers (unlikely, but possible), will be bubbled up to the MachineSetsGenerated status condition. The error message might want to indicate that the user can specify the OSImage explicitly (mp.spec.platform.azure.osImage already exists for this purpose).