On Wed, Oct 21, 2020, at 05:51, Tom Bentley wrote: > Hi Colin, > > On Mon, Oct 19, 2020, at 08:59, Ron Dagostino wrote: > > > Hi Colin. Thanks for the hard work on this KIP. > > > > > > I have some questions about what happens to a broker when it becomes > > > fenced (e.g. because it can't send a heartbeat request to keep its > > > lease). The KIP says "When a broker is fenced, it cannot process any > > > client requests. This prevents brokers which are not receiving > > > metadata updates or that are not receiving and processing them fast > > > enough from causing issues to clients." And in the description of the > > > FENCED(4) state it likewise says "While in this state, the broker does > > > not respond to client requests." It makes sense that a fenced broker > > > should not accept producer requests -- I assume any such requests > > > would result in NotLeaderOrFollowerException. But what about KIP-392 > > > (fetch from follower) consumer requests? It is conceivable that these > > > could continue. Related to that, would a fenced broker continue to > > > fetch data for partitions where it thinks it is a follower? Even if > > > it rejects consumer requests it might still continue to fetch as a > > > follower. Might it be helpful to clarify both decisions here? > > > > Hi Ron, > > > > Good question. I think a fenced broker should continue to fetch on > > partitions it was already fetching before it was fenced, unless it hits a > > problem. At that point it won't be able to continue, since it doesn't have > > the new metadata. For example, it won't know about leadership changes in > > the partitions it's fetching. The rationale for continuing to fetch is to > > try to avoid disruptions as much as possible. > > > > I don't think fenced brokers should accept client requests. The issue is > > that the fenced broker may or may not have any data it is supposed to > > have. It may or may not have applied any configuration changes, etc. that > > it is supposed to have applied. So it could get pretty confusing, and also > > potentially waste the client's time. > > > > > When fenced, how would the broker reply to a client which did make a > request? >
Hi Tom, The broker will respond with a retryable error in that case. Once the client has re-fetched its metadata, it will no longer see the fenced broker as part of the cluster. I added a note to the KIP. best, Colin > > Thanks, > > Tom >
