One more thing I would like to see deprecated (hopefully no one mentioned before) is the zk based consumer offset support.
On Mon, May 11, 2020 at 2:15 PM Colin McCabe <cmcc...@apache.org> wrote: > Hi Michael, > > It would be better to discuss the background behind KIP-500 in a separate > thread, since this thread is about the Kafka 3.0 release. As others have > said, your questions are answered in the KIP. For example, "what is the > actual goal?" is addressed in the motivation section. > > I agree that Kafka's usage of Apache ZooKeeper could be optimized. But > there are fundamental limitations to this approach compared to storing our > metadata internally. For example, having to contact a remote server to > reload all your metadata on a controller failover simply doesn't scale past > a certain point. > > Apache Curator is a nice API, and if we were starting again today we would > certainly consider using it. But it doesn't allow us to do anything more > efficiently than ZooKeeper could already do it. > > Finally, Kafka's core competence is logs. While our replication protocol > is not Raft, it shares many similarities with that protocol. So I think > it's a bit unfair to say that it is "catastrophic hubris" to believe we can > implement the protocol. > > best, > Colin > > > On Sun, May 10, 2020, at 11:02, Michael K. Edwards wrote: > > Yes, I've read the KIP. But all it really says to me is "we have never > > gotten around to using ZooKeeper properly." To the extent that any of > the > > distributed-state-maintenance problems discussed in "Metadata as an Event > > Log" can be solved — and some of them intrinsically can't, because CAP > > theorem — most of them are already implemented very effectively in > Curator > > recipes. (For instance, Curator's Tree Cache > > https://curator.apache.org/curator-recipes/tree-cache.html is a good > fit to > > some of the state-maintenance needs.) > > > > Kafka does have some usage patterns that don't map neatly onto existing > > Curator recipes. For instance, neither LeaderSelector nor LeaderLatch > > implements leader preference in the way that the existing Kafka partition > > leadership election procedure does. But why not handle that by improving > > and extending Curator? That way, other Curator users benefit, and we get > > additional highly experienced reviewers' eyes on the distributed > > algorithms, which are very very tricky to get right. > > > > > > On Sun, May 10, 2020 at 10:47 AM Ron Dagostino <rndg...@gmail.com> > wrote: > > > > > Hi Michael. This is discussed in the KIP. > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-500%3A+Replace+ZooKeeper+with+a+Self-Managed+Metadata+Quorum#KIP-500:ReplaceZooKeeperwithaSelf-ManagedMetadataQuorum-Motivation > > > > > > Ron > > > > > > > On May 10, 2020, at 1:35 PM, Michael K. Edwards < > m.k.edwa...@gmail.com> > > > wrote: > > > > > > > > What is the actual goal of removing the ZooKeeper dependency? In my > > > > experience, if ZooKeeper is properly provisioned and deployed, it's > > > largely > > > > trouble-free. (You do need to know how to use observers properly.) > > > There > > > > are some subtleties about timeouts and leadership changes, but > they're > > > > pretty small stuff. Why go to all the trouble of building a new > > > > distributed-consensus system that's going to have catastrophic bugs > for > > > > years to come? It seems like such an act of hubris to me, as well > as a > > > > massive waste of engineering effort. What is there to be gained? > > > > > > > >> On Fri, May 8, 2020 at 4:11 PM Matthias J. Sax <mj...@apache.org> > > > wrote: > > > >> > > > >> Sure, we can compile a list for Kafka Streams. But the KIP would be > for > > > >> 3.0, so I don't think it's urgent to do it now? > > > >> > > > >> > > > >> -Matthias > > > >> > > > >>> On 5/8/20 3:47 PM, Colin McCabe wrote: > > > >>> Thanks, Guozhang-- sounds like a good plan. > > > >>> > > > >>> I think it would be good to have a list of deprecated streams APIs > that > > > >> we want to remove in 3.0. Maybe it's easiest to do that as its own > KIP? > > > >>> > > > >>> For MirrorMaker 1, we should have a KIP to deprecate its use in > 2.6 if > > > >> we want to remove it in 3.0. I don't have a good sense of how > > > practical it > > > >> is to deprecate this now, so I will defer to others here. But the > KIP > > > >> freeze for 2.6 is coming soon, so if we want to make the case, now > is > > > the > > > >> time. > > > >>> > > > >>> best, > > > >>> Colin > > > >>> > > > >>> > > > >>>> On Thu, May 7, 2020, at 16:28, Guozhang Wang wrote: > > > >>>> Hey folks, > > > >>>> > > > >>>> Sorry for stating that the bridge release would not break any > > > >> compatibility > > > >>>> before, which is incorrect and confused many people. > > > >>>> > > > >>>> I think one way to think about the versioning is that: > > > >>>> > > > >>>> 0) In a 2.x version moving ahead we would deprecate the > ZK-dependent > > > >> tools > > > >>>> such as --zookeeper flags from various scripts (KIP-555) > > > >>>> > > > >>>> 1) In 3.0 we would at least make one incompatible change for > example > > > to > > > >>>> remove the deprecated ZK flags. > > > >>>> > > > >>>> 2) In a future major version (e.g. 4.0) we would drop ZK entirely, > > > >>>> including usages such as security credentials / broker > registration / > > > >> etc > > > >>>> which are via ZK today as well. > > > >>>> > > > >>>> Then for the bridge release(s), it can be any or all of 3.x. > > > >>>> > > > >>>> > > > >>>> For 1), I'd love to add a few more incompatibility changes in 3.0 > from > > > >>>> Kafka Streams: we evolve Streams public APIs by deprecating and > then > > > >> remove > > > >>>> in major releases, and since 2.0 we've accumulated quite a few > > > >> deprecated > > > >>>> APIs, and I can compile a list of KIPs that contain those if > people > > > are > > > >>>> interested. > > > >>>> > > > >>>> > > > >>>> Guozhang > > > >>>> > > > >>>> > > > >>>>> On Thu, May 7, 2020 at 3:53 PM Colin McCabe <cmcc...@apache.org> > > > wrote: > > > >>>>> > > > >>>>> On Wed, May 6, 2020, at 21:33, Ryanne Dolan wrote: > > > >>>>>>> In fact, we know that the bridge release will involve at least > one > > > >>>>>>> incompatible change. We will need to drop support for the > > > >> --zookeeper > > > >>>>>>> flags in the command-line tools. > > > >>>>>> > > > >>>>>> If the bridge release(s) and the subsequent post-ZK release are > > > _both_ > > > >>>>>> breaking changes, I think we only have one option: the 3.x line > are > > > >> the > > > >>>>>> bridge release(s), and ZK is removed in 4.0, as suggested by > Andrew > > > >>>>>> Schofield. > > > >>>>>> > > > >>>>>> Specifically: > > > >>>>>> - in order to _remove_ (not merely deprecate) the --zookeeper > args, > > > we > > > >>>>> will > > > >>>>>> need a major release. > > > >>>>>> - in oder to drop support for ZK entirely (e.g. break a bunch of > > > >> external > > > >>>>>> tooling like Cruise Control), we will need a major release. > > > >>>>>> > > > >>>>>> I count two major releases. > > > >>>>> > > > >>>>> Hi Ryanne, > > > >>>>> > > > >>>>> I agree that dropping ZK completely will need a new major release > > > after > > > >>>>> 3.0. I think that's OK and in keeping with how we've handled > > > >> deprecation > > > >>>>> and removal in the past. It's important for users to have a > smooth > > > >> upgrade > > > >>>>> path. > > > >>>>> > > > >>>>> best, > > > >>>>> Colin > > > >>>>> > > > >>>>>> > > > >>>>>> Ryanne > > > >>>>>> > > > >>>>>> - > > > >>>>>> > > > >>>>>> On Wed, May 6, 2020 at 10:52 PM Colin McCabe < > cmcc...@apache.org> > > > >> wrote: > > > >>>>>> > > > >>>>>>>> On Mon, May 4, 2020, at 17:12, Ryanne Dolan wrote: > > > >>>>>>>> Hey Colin, I think we should wait until after KIP-500's > "bridge > > > >>>>>>>> release" so there is a clean break from Zookeeper after 3.0. > The > > > >>>>>>>> bridge release by definition is an attempt to not break > anything, > > > so > > > >>>>>>>> it theoretically doesn't warrant a major release. > > > >>>>>>> > > > >>>>>>> Hi Ryanne, > > > >>>>>>> > > > >>>>>>> I think it's important to clarify this a little bit. The > bridge > > > >>>>> release > > > >>>>>>> (really, releases, plural) allow you to upgrade from a cluster > that > > > >> is > > > >>>>>>> using ZooKeeper to one that is not using ZooKeeper. But, that > > > >> doesn't > > > >>>>>>> imply that the bridge release itself doesn't break anything. > > > >> Upgrading > > > >>>>>>> to the bridge release itself might involve some minor > > > >> incompatibility. > > > >>>>>>> > > > >>>>>>> Kafka does occasionally have incompatible changes. In those > cases, > > > >> we > > > >>>>>>> bump the major version number. One example is that when we > went > > > from > > > >>>>>>> Kafka 1.x to Kafka 2.0, we dropped support for JDK7. This is > an > > > >>>>>>> incompatible change. > > > >>>>>>> > > > >>>>>>> In fact, we know that the bridge release will involve at least > one > > > >>>>>>> incompatible change. We will need to drop support for the > > > >> --zookeeper > > > >>>>>>> flags in the command-line tools. > > > >>>>>>> > > > >>>>>>> We've been preparing for this change for a long time. People > have > > > >>>>> spent > > > >>>>>>> a lot of effort designing new APIs that can be used instead of > the > > > >> old > > > >>>>>>> zookeeper-based code that some of the command-line tools > used. We > > > >> have > > > >>>>>>> also deprecated the old ZK-based flags. But at the end of the > day, > > > >> it > > > >>>>>>> is still an incompatible change. So it's unfortunately not > > > possible > > > >>>>> for > > > >>>>>>> the > > > >>>>>>> bridge release to be a 2.x release. > > > >>>>>>> > > > >>>>>>>> If that's not the case (i.e. if a single "bridge release" > turns > > > out > > > >>>>> to > > > >>>>>>>> be impractical), we should consider forking 3.0 while > maintaining > > > a > > > >>>>>>>> line of Zookeeper-dependent Kafka in 2.x. That way 3.x can > evolve > > > >>>>>>>> dramatically without breaking the 2.x line. In particular, > > > anything > > > >>>>>>>> related to removing Zookeeper could land in pre-3.0 while > every > > > >> other > > > >>>>>>>> feature targets 2.6. > > > >>>>>>> > > > >>>>>>> Just to be super clear about this, what we want to do here is > > > support > > > >>>>>>> operating in __either__ KIP-500 mode and legacy mode for a > while. > > > So > > > >>>>> the > > > >>>>>>> same branch will have support for both the old way and the new > way > > > of > > > >>>>>>> managing metadata. > > > >>>>>>> > > > >>>>>>> This will allow us to get an "alpha" version of the KIP-500 > mode > > > out > > > >>>>> early > > > >>>>>>> for people to experiment with. It also greatly reduces the > number > > > of > > > >>>>> Kafka > > > >>>>>>> releases we have to make, and the amount of backporting we > have to > > > >> do. > > > >>>>>>> > > > >>>>>>>> > > > >>>>>>>> If you are proposing 2.6 should be the "bridge release", I > think > > > >> this > > > >>>>>>>> is premature given Kafka's time-based release schedule. If the > > > >> bridge > > > >>>>>>>> features happen to be merged before 2.6's feature freeze, then > > > sure > > > >>>>> -- > > > >>>>>>>> let's make that the bridge release in retrospect. And if we > get > > > all > > > >>>>>>>> the post-Zookeeper features merged before 2.7, I'm onboard > with > > > >>>>> naming > > > >>>>>>>> it "3.0" instead. > > > >>>>>>>> > > > >>>>>>>> That said, we should aim to remove legacy MirrorMaker before > 3.0 > > > as > > > >>>>>>>> well. I'm happy to drive that additional breaking change. > Maybe > > > 2.6 > > > >>>>>>>> can be the "bridge" for MM2 as well. > > > >>>>>>> > > > >>>>>>> I don't have a strong opinion either way about this, but if we > want > > > >> to > > > >>>>>>> remove the original MirrorMaker, we have to deprecate it first, > > > >>>>> right? Are > > > >>>>>>> we ready to do that? > > > >>>>>>> > > > >>>>>>> best, > > > >>>>>>> Colin > > > >>>>>>> > > > >>>>>>>> > > > >>>>>>>> Ryanne > > > >>>>>>>> > > > >>>>>>>> On Mon, May 4, 2020, 5:05 PM Colin McCabe <cmcc...@apache.org > > > > > >>>>> wrote: > > > >>>>>>>> > > > >>>>>>>>> Hi all, > > > >>>>>>>>> > > > >>>>>>>>> We've had a few proposals recently for incompatible > changes. One > > > >>>>> of > > > >>>>>>>>> them is my KIP-604: Remove ZooKeeper Flags from the > > > Administrative > > > >>>>>>>>> Tools. The other is Boyang's KIP-590: Redirect ZK Mutation > > > >>>>>>>>> Protocols to the Controller. I think it's time to start > thinking > > > >>>>>>>>> about Kafka 3.0. Specifically, I think we should move to 3.0 > > > after > > > >>>>>>>>> the 2.6 release. > > > >>>>>>>>> > > > >>>>>>>>> From the perspective of KIP-500, in Kafka 3.x we'd like to > make > > > >>>>>>>>> running in a ZooKeeper-less mode possible (but not yet the > > > >>>>> default.) > > > >>>>>>>>> This is the motivation behind KIP-590 and KIP-604, as well as > > > some > > > >>>>>>>>> of the other KIPs we've done recently. Since it will take > some > > > >>>>> time > > > >>>>>>>>> to stabilize the new ZooKeeper-free Kafka code, we will hide > it > > > >>>>>>>>> behind an option initially. (We'll have a KIP describing > this all > > > >>>>> in > > > >>>>>>>>> detail soon.) > > > >>>>>>>>> > > > >>>>>>>>> What does everyone think about having Kafka 3.0 come up next > > > after > > > >>>>>>>>> 2.6? Are there any other things we should change in the 2.6 > -> > > > 3.0 > > > >>>>>>>>> transition? > > > >>>>>>>>> > > > >>>>>>>>> best, Colin > > > >>>>>>>>> > > > >>>>>>>> > > > >>>>>>> > > > >>>>>> > > > >>>>> > > > >>>> > > > >>>> > > > >>>> -- > > > >>>> -- Guozhang > > > >>>> > > > >> > > > >> > > > > > >
