Thanks! AH2: I see, and it would also be unsupported/operator-error to attempt to unregister a controller while it is still running.
On Fri, Apr 3, 2026 at 1:38 PM Kevin Wu <[email protected]> wrote: > Hi Alyssa, > > Thanks for the questions. > > RE AH2: You could also unregister a controller via the `kafka-cluster > unregister-controller` command I am proposing in this KIP. Invoking either > CLI command being introduced in this KIP with the wrong controller id can > result in an operator accidentally unregistering a controller which is > still running (has not been decommissioned). In this case, the controller > needs to re-register since it is still part of the kafka cluster. > > RE AH3: Let me fix this sentence. I mean "The intention for unregistration > is for it to occur after the operator decommissions a controller node. This > means the node is no longer part of the kafka cluster, and the controller > process associated with this node is not expected to come back." The > unregister CLI command will return something to the user based on the > UnregsiterControllerResponse. > > Best, > Kevin Wu > > On Fri, Apr 3, 2026 at 3:27 PM Alyssa Huang via dev <[email protected]> > wrote: > > > Few more questions actually > > > > AH1 > > Thanks, I was mainly trying to understand if dynamic reconfiguration > offers > > an incomplete downscaling UX without this KIP. Seems like that's the > case. > > I also missed the scenario with observer controllers so thanks for > > clarifying that part. > > > > AH2 > > > > > The registration manager of an unregistered controller should attempt > to > > > re-register with the active controller. This is to prevent accidental > > > unregistrations. > > > > I'm not sure if this makes sense to me, what would be an accidental > > unregistration? Is the only trigger for unregistration the new > > remove-controller command you're adding? > > > > AH3 > > > > > The intention for unregistration is for it to occur after the operator > > > decommissions a node which will no longer be part of the kafka cluster, > > and > > > is not expected to return. > > > > Why isn't the command expected to return? > > > > Thanks! > > > > On Fri, Apr 3, 2026 at 12:15 PM Alyssa Huang <[email protected]> > wrote: > > > > > Thanks for the KIP Kevin! > > > > > > AH1 > > > > > >> This means a stale controller registration from a controller that no > > >> longer exists can block feature upgrades. > > > > > > > > > And dynamic reconfiguration (specifically RemoveVoter) can cause stale > > > controller registrations? Meaning anyone who has used RemoveVoter to > > > permanently downsize their controller quorum would eventually need to > > > unregister the controller to unblock future feature upgrades? > > > > > > Best, > > > Alyssa > > > > > > On Fri, Apr 3, 2026 at 11:30 AM Kevin Wu <[email protected]> > wrote: > > > > > >> Hi all, > > >> > > >> I would like to start a discussion on KIP-1312: Support unregistering > > >> controllers. Below is the KIP link. > > >> > > >> > > >> > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-1312%3A+Support+unregistering+controllers > > >> > > >> Thanks, > > >> Kevin Wu > > >> > > > > > >
