Page History

...

It is possible that brokers and controllers attempt to join the cluster or quorum, but cannot support the current metadata.version. For brokers, this is already handled by the controller during registration. If a broker attempts to register with the controller, but the controller determines that the broker cannot support the current set of finalized features (which includes metadata.version), it will reject the registration request. For controllers, it is more complicated since we need to allow the quorum to be established in order to allow records to be exchanged and learn about the new metadata.version. A controller running old software will join the quorum and begin replicating the metadata log. If this inactive controller encounters a FeatureLevelRecord for metadata.version that it cannot support, it should terminate.

In the unlikely even event that an active controller encounters an unsupported metadata.version, it should resign and terminate. 

...