A few additional questions: 1. Currently the IBP tells us what version of individual inter-broker RPCs will be used. I think the plan in this KIP is to use ApiVersions request instead to find the highest compatible version (just like clients). Do I have that right?
2. The following wasn't very clear to me: > Brokers will be able to observe changes to metadata.version by observing the metadata log, and could then submit a new ApiVersionsRequest to the other Kafka nodes. Is the purpose of submitting new ApiVersions requests to update the features or the RPC versions? Does metadata.version also influence the versions that a broker advertises? It would help to have more detail about this. 3. I imagine users will want to know before performing an upgrade whether downgrading will be safe. Would the --dry-run flag tell them this? Thanks, Jason On Wed, Nov 17, 2021 at 3:55 PM Colin McCabe <cmcc...@apache.org> wrote: > On Wed, Nov 17, 2021, at 11:28, Jason Gustafson wrote: > > Hi David, > > > > Forgive me if this ground has been covered already. Today, we have a few > > other things that we have latched onto the IBP, such as upgrades to the > > format of records in __consumer_offsets. I've been assuming that > > metadata.version is not covering this. Is that right or is there some > other > > plan to take care of cases like this? > > > > I think metadata.version could cover changes to things like > __consumer_offsets, if people want it to. Or to put it another way, that is > out of scope for this KIP. > > Like David said, basically it boils down to creating a feature flag for > the new proposed __consumer_offsets version, or using a new > IBP/metadata.version for it. Both approaches have pros and cons. Using an > IBP/metadata.version bump reduces the size of the testing matrix. But using > a feature flag allows people to avoid any bugs or pain associated with the > change if they don't care about enabling it. This is basically the classic > "should I use a feature flag or not?" discussion and we need to have it on > a case-by-case basis. > > I think it's worth calling out that having a 1:1 mapping between IBP > versions and metadata.versions will result in some metadata.versions that > "don't do anything" (aka they do the same thing as the previous > metadata.version). For example, if we change StopReplicaRequest again, that > will not affect KRaft mode, but probably would require an IBP bump and > hence a metadata.version bump. I think that's OK. It's not that different > from updating your IBP and getting support for ZStandard, when your > deployment doesn't use ZStandard compression. > > best, > Colin > > > Thanks, > > Jason > > > > > > > > On Wed, Nov 17, 2021 at 10:17 AM Jun Rao <j...@confluent.io.invalid> > wrote: > > > >> Hi, Colin, > >> > >> Thanks for the reply. > >> > >> For case b, I am not sure that I understand your suggestion. Does "each > >> subsequent level for metadata.version corresponds to an IBP version" > mean > >> that we need to keep IBP forever? Could you describe the upgrade > process in > >> this case? > >> > >> Jun > >> > >> On Tue, Nov 16, 2021 at 3:45 PM Colin McCabe <cmcc...@apache.org> > wrote: > >> > >> > On Tue, Nov 16, 2021, at 15:13, Jun Rao wrote: > >> > > Hi, David, Colin, > >> > > > >> > > Thanks for the reply. > >> > > > >> > > 16. Discussed with David offline a bit. We have 3 cases. > >> > > a. We upgrade from an old version where the metadata.version has > >> already > >> > > been finalized. In this case it makes sense to stay with that > feature > >> > > version after the upgrade. > >> > > >> > +1 > >> > > >> > > b. We upgrade from an old version where no metadata.version has been > >> > > finalized. In this case, it makes sense to leave metadata.version > >> > disabled > >> > > since we don't know if all brokers have been upgraded. > >> > > >> > This is the scenario I was hoping to avoid by saying that ALL KRaft > >> > clusters have metadata.version of at least 1, and each subsequent > level > >> for > >> > metadata.version corresponds to an IBP version. The existing KRaft > >> clusters > >> > in 3.0 and earlier are preview (not for production) so I think this > >> change > >> > is OK for 3.x (given that it affects only KRaft). Then IBP is > irrelevant > >> > for KRaft clusters (the config is ignored, possibly with a WARN or > ERROR > >> > message generated if it is set). > >> > > >> > > c. We are starting from a brand new cluster and of course no > >> > > metadata.version has been finalized. In this case, the KIP says it > will > >> > > pick the metadata.version in meta.properties. In the common case, > >> people > >> > > probably won't set the metadata.version in the meta.properties file > >> > > explicitly. So, it will be useful to put a default (stable) version > >> there > >> > > when the meta.properties. > >> > > >> > Hmm. I was assuming that clusters where the admin didn't specify any > >> > metadata.version during formatting would get the latest > metadata.version. > >> > Partly, because this is what we do for IBP today. It would be good to > >> > clarify this... > >> > > >> > > > >> > > Also, it would be useful to clarify that if a FeatureLevelRecord > exists > >> > for > >> > > metadata.version, the metadata.version in meta.properties will be > >> > ignored. > >> > > > >> > > >> > Yeah, I agree. > >> > > >> > best, > >> > Colin > >> > > >> > > Thanks, > >> > > > >> > > Jun > >> > > > >> > > > >> > > On Tue, Nov 16, 2021 at 12:39 PM Colin McCabe <cmcc...@apache.org> > >> > wrote: > >> > > > >> > >> On Fri, Nov 5, 2021, at 15:18, Jun Rao wrote: > >> > >> > Hi, David, > >> > >> > > >> > >> > Thanks for the reply. > >> > >> > > >> > >> > 16. My first concern is that the KIP picks up meta.version > >> > inconsistently > >> > >> > during the deployment. If a new cluster is started, we pick up > the > >> > >> highest > >> > >> > version. If we upgrade, we leave the feature version unchanged. > >> > >> > >> > >> Hi Jun, > >> > >> > >> > >> Thanks again for taking a look. > >> > >> > >> > >> The proposed behavior in KIP-778 is consistent with how it works > >> today. > >> > >> Upgrading the software is distinct from upgrading the IBP. > >> > >> > >> > >> I think it is important to keep these two operations ("upgrading > >> > >> IBP/metadata version" and "upgrading software version") separate. > If > >> > they > >> > >> are coupled it will create a situation where software upgrades are > >> > >> difficult and dangerous. > >> > >> > >> > >> Consider a situation where you find some bug in your current > software, > >> > and > >> > >> you want to upgrade to new software that fixes the bug. If upgrades > >> and > >> > IBP > >> > >> bumps are coupled, you can't do this without also bumping the IBP, > >> > which is > >> > >> usually considered a high-risk change. That means that either you > have > >> > to > >> > >> make a special build that includes only the fix (time-consuming and > >> > >> error-prone), live with the bug for longer, or be very conservative > >> > about > >> > >> ever introducing new IBP/metadata versions. None of those are > really > >> > good > >> > >> choices. > >> > >> > >> > >> > Intuitively, it seems that independent of how a cluster is > deployed, > >> > we > >> > >> > should always pick the same feature version. > >> > >> > >> > >> I think it makes sense to draw a distinction between upgrading an > >> > existing > >> > >> cluster and deploying a new one. What most people want out of > upgrades > >> > is > >> > >> that things should keep working, but with bug fixes. If we change > >> that, > >> > it > >> > >> just makes people more reluctant to upgrade (which is always a > >> > problem...) > >> > >> > >> > >> > I think we need to think this through in this KIP. My second > concern > >> > is > >> > >> > that as a particular version matures, it's inconvenient for a > user > >> to > >> > >> manually > >> > >> > upgrade every feature version. As long as we have a path to > achieve > >> > that > >> > >> in > >> > >> > the future, we don't need to address that in this KIP. > >> > >> > >> > >> If people are managing a large number of Kafka clusters, they will > >> want > >> > to > >> > >> do some sort of A/B testing with IBP/metadata versions. So if you > have > >> > 1000 > >> > >> Kafka clusters, you roll out the new IBP version to 10 of them and > see > >> > how > >> > >> it goes. If that goes well, you roll it out to more, etc. > >> > >> > >> > >> So, the automation needs to be at the cluster management layer, > not at > >> > the > >> > >> Kafka layer. Each Kafka cluster doesn't know how well things went > in > >> the > >> > >> other 999 clusters. Automatically upgrading is a bad thing for the > >> same > >> > >> reason Kafka automatically upgrading its own software version would > >> be a > >> > >> bad thing -- it could lead to a disruption to a sensitive cluster > at > >> the > >> > >> wrong time. > >> > >> > >> > >> For people who are just managing one or two Kafka clusters, > >> > automatically > >> > >> upgrading feature versions isn't a big burden and can be done > >> manually. > >> > >> This is all consistent with how IBP works today. > >> > >> > >> > >> Also, we already have a command-line option to the feature tool > which > >> > >> upgrades all features to the latest available, if that is what the > >> > >> administrator desires. Perhaps we could add documentation saying > that > >> > this > >> > >> should be done as the last step of the upgrade. > >> > >> > >> > >> best, > >> > >> Colin > >> > >> > >> > >> > > >> > >> > 21. "./kafka-features.sh delete": Deleting a feature seems a bit > >> weird > >> > >> > since the logic is always there. Would it be better to use > disable? > >> > >> > > >> > >> > Jun > >> > >> > > >> > >> > On Fri, Nov 5, 2021 at 8:11 AM David Arthur > >> > >> > <david.art...@confluent.io.invalid> wrote: > >> > >> > > >> > >> >> Colin and Jun, thanks for the additional comments! > >> > >> >> > >> > >> >> Colin: > >> > >> >> > >> > >> >> > We've been talking about having an automated RPC compatibility > >> > checker > >> > >> >> > >> > >> >> Do we have a way to mark fields in schemas as deprecated? It can > >> > stay in > >> > >> >> the RPC, it just complicates the logic a bit. > >> > >> >> > >> > >> >> > It would be nice if the active controller could validate that > a > >> > >> majority > >> > >> >> of the quorum could use the proposed metadata.version. The > active > >> > >> >> controller should have this information, right? If we don't have > >> > recent > >> > >> >> information from a quorum of voters, we wouldn't be active. > >> > >> >> > >> > >> >> I believe we should have this information from the > >> > ApiVersionsResponse. > >> > >> It > >> > >> >> would be good to do this validation to avoid a situation where a > >> > >> >> quorum leader can't be elected due to unprocessable records. > >> > >> >> > >> > >> >> > Do we need delete as a command separate from downgrade? > >> > >> >> > >> > >> >> I think from an operator's perspective, it is nice to > distinguish > >> > >> between > >> > >> >> changing a feature flag and unsetting it. It might be > surprising to > >> > an > >> > >> >> operator to see the flag's version set to nothing when they > >> requested > >> > >> the > >> > >> >> downgrade to version 0 (or less). > >> > >> >> > >> > >> >> > it seems like we should spell out that metadata.version > begins at > >> > 1 in > >> > >> >> KRaft clusters > >> > >> >> > >> > >> >> I added this text: > >> > >> >> > >> > >> >> Introduce an IBP version to indicate the lowest software version > >> that > >> > >> >> > supports *metadata.version*. Below this IBP, the > >> > *metadata.version* is > >> > >> >> > undefined and will not be examined. At or above this IBP, the > >> > >> >> > *metadata.version* must be *0* for ZooKeeper clusters and > will be > >> > >> >> > initialized as *1* for KRaft clusters. > >> > >> >> > >> > >> >> > >> > >> >> > We probably also want an RPC implemented by both brokers and > >> > >> controllers > >> > >> >> that will reveal the min and max supported versions for each > >> feature > >> > >> level > >> > >> >> supported by the server > >> > >> >> > >> > >> >> This is available in ApiVersionsResponse (we include the > server's > >> > >> supported > >> > >> >> features as well as the cluster's finalized features) > >> > >> >> > >> > >> >> -------- > >> > >> >> > >> > >> >> Jun: > >> > >> >> > >> > >> >> 12. I've updated the KIP with AdminClient changes > >> > >> >> > >> > >> >> 14. You're right, it looks like I missed a few sections > regarding > >> > >> snapshot > >> > >> >> generation. I've corrected it > >> > >> >> > >> > >> >> 16. This feels more like an enhancement to KIP-584. I agree it > >> could > >> > be > >> > >> >> useful, but perhaps we could address it separately from KRaft > >> > upgrades? > >> > >> >> > >> > >> >> 20. Indeed snapshots are not strictly necessary during an > upgrade, > >> > I've > >> > >> >> reworded this > >> > >> >> > >> > >> >> > >> > >> >> Thanks! > >> > >> >> David > >> > >> >> > >> > >> >> > >> > >> >> On Thu, Nov 4, 2021 at 6:51 PM Jun Rao <j...@confluent.io.invalid > > > >> > >> wrote: > >> > >> >> > >> > >> >> > Hi, David, Jose and Colin, > >> > >> >> > > >> > >> >> > Thanks for the reply. A few more comments. > >> > >> >> > > >> > >> >> > 12. It seems that we haven't updated the AdminClient > accordingly? > >> > >> >> > > >> > >> >> > 14. "Metadata snapshot is generated and sent to the other > >> inactive > >> > >> >> > controllers and to brokers". I thought we wanted each broker > to > >> > >> generate > >> > >> >> > its own snapshot independently? If only the controller > generates > >> > the > >> > >> >> > snapshot, how do we force other brokers to pick it up? > >> > >> >> > > >> > >> >> > 16. If a feature version is new, one may not want to enable it > >> > >> >> immediately > >> > >> >> > after the cluster is upgraded. However, if a feature version > has > >> > been > >> > >> >> > stable, requiring every user to run a command to upgrade to > that > >> > >> version > >> > >> >> > seems inconvenient. One way to improve this is for each > feature > >> to > >> > >> define > >> > >> >> > one version as the default. Then, when we upgrade a cluster, > we > >> > will > >> > >> >> > automatically upgrade the feature to the default version. An > >> admin > >> > >> could > >> > >> >> > use the tool to upgrade to a version higher than the default. > >> > >> >> > > >> > >> >> > 20. "The quorum controller can assist with this process by > >> > generating > >> > >> a > >> > >> >> > metadata snapshot after a metadata.version increase has been > >> > >> committed to > >> > >> >> > the metadata log. This snapshot will be a convenient way to > let > >> > broker > >> > >> >> and > >> > >> >> > controller components rebuild their entire in-memory state > >> > following > >> > >> an > >> > >> >> > upgrade." The new version of the software could read both the > new > >> > and > >> > >> the > >> > >> >> > old version. Is generating a new snapshot during upgrade > needed? > >> > >> >> > > >> > >> >> > Jun > >> > >> >> > > >> > >> >> > > >> > >> >> > On Wed, Nov 3, 2021 at 5:42 PM Colin McCabe < > cmcc...@apache.org> > >> > >> wrote: > >> > >> >> > > >> > >> >> > > On Tue, Oct 12, 2021, at 10:34, Jun Rao wrote: > >> > >> >> > > > Hi, David, > >> > >> >> > > > > >> > >> >> > > > One more comment. > >> > >> >> > > > > >> > >> >> > > > 16. The main reason why KIP-584 requires finalizing a > feature > >> > >> >> manually > >> > >> >> > is > >> > >> >> > > > that in the ZK world, the controller doesn't know all > brokers > >> > in a > >> > >> >> > > cluster. > >> > >> >> > > > A broker temporarily down is not registered in ZK. in the > >> KRaft > >> > >> >> world, > >> > >> >> > > the > >> > >> >> > > > controller keeps track of all brokers, including those > that > >> are > >> > >> >> > > temporarily > >> > >> >> > > > down. This makes it possible for the controller to > >> > automatically > >> > >> >> > > finalize a > >> > >> >> > > > feature---it's safe to do so when all brokers support that > >> > >> feature. > >> > >> >> > This > >> > >> >> > > > will make the upgrade process much simpler since no manual > >> > >> command is > >> > >> >> > > > required to turn on a new feature. Have we considered > this? > >> > >> >> > > > > >> > >> >> > > > Thanks, > >> > >> >> > > > > >> > >> >> > > > Jun > >> > >> >> > > > >> > >> >> > > Hi Jun, > >> > >> >> > > > >> > >> >> > > I guess David commented on this point already, but I'll > comment > >> > as > >> > >> >> well. > >> > >> >> > I > >> > >> >> > > always had the perception that users viewed rolls as > >> potentially > >> > >> risky > >> > >> >> > and > >> > >> >> > > were looking for ways to reduce the risk. Not enabling > features > >> > >> right > >> > >> >> > away > >> > >> >> > > after installing new software seems like one way to do > that. If > >> > we > >> > >> had > >> > >> >> a > >> > >> >> > > feature to automatically upgrade during a roll, I'm not sure > >> > that I > >> > >> >> would > >> > >> >> > > recommend that people use it, because if something fails, it > >> > makes > >> > >> it > >> > >> >> > > harder to tell if the new feature is at fault, or something > >> else > >> > in > >> > >> the > >> > >> >> > new > >> > >> >> > > software. > >> > >> >> > > > >> > >> >> > > We already tell users to do a "double roll" when going to a > new > >> > IBP. > >> > >> >> > (Just > >> > >> >> > > to give background to people who haven't heard that phrase, > the > >> > >> first > >> > >> >> > roll > >> > >> >> > > installs the new software, and the second roll updates the > >> IBP). > >> > So > >> > >> >> this > >> > >> >> > > KIP-778 mechanism is basically very similar to that, except > the > >> > >> second > >> > >> >> > > thing isn't a roll, but just an upgrade command. So I think > >> this > >> > is > >> > >> >> > > consistent with what we currently do. > >> > >> >> > > > >> > >> >> > > Also, just like David said, we can always add auto-upgrade > >> later > >> > if > >> > >> >> there > >> > >> >> > > is demand... > >> > >> >> > > > >> > >> >> > > best, > >> > >> >> > > Colin > >> > >> >> > > > >> > >> >> > > > >> > >> >> > > > > >> > >> >> > > > On Thu, Oct 7, 2021 at 5:19 PM Jun Rao <j...@confluent.io> > >> > wrote: > >> > >> >> > > > > >> > >> >> > > >> Hi, David, > >> > >> >> > > >> > >> > >> >> > > >> Thanks for the KIP. A few comments below. > >> > >> >> > > >> > >> > >> >> > > >> 10. It would be useful to describe how the controller > node > >> > >> >> determines > >> > >> >> > > the > >> > >> >> > > >> RPC version used to communicate to other controller > nodes. > >> > There > >> > >> >> seems > >> > >> >> > > to > >> > >> >> > > >> be a bootstrap problem. A controller node can't read the > log > >> > and > >> > >> >> > > >> therefore the feature level until a quorum leader is > >> elected. > >> > But > >> > >> >> > leader > >> > >> >> > > >> election requires an RPC. > >> > >> >> > > >> > >> > >> >> > > >> 11. For downgrades, it would be useful to describe how to > >> > >> determine > >> > >> >> > the > >> > >> >> > > >> downgrade process (generating new snapshot, propagating > the > >> > >> >> snapshot, > >> > >> >> > > etc) > >> > >> >> > > >> has completed. We could block the UpdateFeature request > >> until > >> > the > >> > >> >> > > process > >> > >> >> > > >> is completed. However, since the process could take time, > >> the > >> > >> >> request > >> > >> >> > > could > >> > >> >> > > >> time out. Another way is through DescribeFeature and the > >> > server > >> > >> only > >> > >> >> > > >> reports downgraded versions after the process is > completed. > >> > >> >> > > >> > >> > >> >> > > >> 12. Since we are changing UpdateFeaturesRequest, do we > need > >> to > >> > >> >> change > >> > >> >> > > the > >> > >> >> > > >> AdminClient api for updateFeatures too? > >> > >> >> > > >> > >> > >> >> > > >> 13. For the paragraph starting with "In the absence of an > >> > >> operator > >> > >> >> > > >> defined value for metadata.version", in KIP-584, we > >> described > >> > >> how to > >> > >> >> > > >> finalize features with New cluster bootstrap. In that > case, > >> > it's > >> > >> >> > > >> inconvenient for the users to have to run an admin tool > to > >> > >> finalize > >> > >> >> > the > >> > >> >> > > >> version for each feature. Instead, the system detects > that > >> the > >> > >> >> > /features > >> > >> >> > > >> path is missing in ZK and thus automatically finalizes > every > >> > >> feature > >> > >> >> > > with > >> > >> >> > > >> the latest supported version. Could we do something > similar > >> in > >> > >> the > >> > >> >> > KRaft > >> > >> >> > > >> mode? > >> > >> >> > > >> > >> > >> >> > > >> 14. After the quorum leader generates a new snapshot, > how do > >> > we > >> > >> >> force > >> > >> >> > > >> other nodes to pick up the new snapshot? > >> > >> >> > > >> > >> > >> >> > > >> 15. I agree with Jose that it will be useful to describe > >> when > >> > >> >> > > generating a > >> > >> >> > > >> new snapshot is needed. To me, it seems the new snapshot > is > >> > only > >> > >> >> > needed > >> > >> >> > > >> when incompatible changes are made. > >> > >> >> > > >> > >> > >> >> > > >> 7. Jose, what control records were you referring? > >> > >> >> > > >> > >> > >> >> > > >> Thanks, > >> > >> >> > > >> > >> > >> >> > > >> Jun > >> > >> >> > > >> > >> > >> >> > > >> > >> > >> >> > > >> On Tue, Oct 5, 2021 at 8:53 AM David Arthur < > >> > >> davidart...@apache.org > >> > >> >> > > >> > >> >> > > >> wrote: > >> > >> >> > > >> > >> > >> >> > > >>> Jose, thanks for the thorough review and comments! > >> > >> >> > > >>> > >> > >> >> > > >>> I am out of the office until next week, so I probably > won't > >> > be > >> > >> able > >> > >> >> > to > >> > >> >> > > >>> update the KIP until then. Here are some replies to your > >> > >> questions: > >> > >> >> > > >>> > >> > >> >> > > >>> 1. Generate snapshot on upgrade > >> > >> >> > > >>> > > Metadata snapshot is generated and sent to the other > >> > nodes > >> > >> >> > > >>> > Why does the Active Controller need to generate a new > >> > snapshot > >> > >> >> and > >> > >> >> > > >>> > force a snapshot fetch from the replicas (inactive > >> > controller > >> > >> and > >> > >> >> > > >>> > brokers) on an upgrade? Isn't writing the > >> > FeatureLevelRecord > >> > >> good > >> > >> >> > > >>> > enough to communicate the upgrade to the replicas? > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> You're right, we don't necessarily need to _transmit_ a > >> > >> snapshot, > >> > >> >> > since > >> > >> >> > > >>> each node can generate its own equivalent snapshot > >> > >> >> > > >>> > >> > >> >> > > >>> 2. Generate snapshot on downgrade > >> > >> >> > > >>> > > Metadata snapshot is generated and sent to the other > >> > >> inactive > >> > >> >> > > >>> > controllers and to brokers (this snapshot may be > lossy!) > >> > >> >> > > >>> > Why do we need to send this downgraded snapshot to the > >> > >> brokers? > >> > >> >> The > >> > >> >> > > >>> > replicas have seen the FeatureLevelRecord and noticed > the > >> > >> >> > downgrade. > >> > >> >> > > >>> > Can we have the replicas each independently generate a > >> > >> downgraded > >> > >> >> > > >>> > snapshot at the offset for the downgraded > >> > FeatureLevelRecord? > >> > >> I > >> > >> >> > > assume > >> > >> >> > > >>> > that the active controller will guarantee that all > >> records > >> > >> after > >> > >> >> > the > >> > >> >> > > >>> > FatureLevelRecord use the downgraded version. If so, > it > >> > would > >> > >> be > >> > >> >> > good > >> > >> >> > > >>> > to mention that explicitly. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> Similar to above, yes a broker that detects a downgrade > via > >> > >> >> > > >>> FeatureLevelRecord could generate its own downgrade > >> snapshot > >> > and > >> > >> >> > reload > >> > >> >> > > >>> its > >> > >> >> > > >>> state from that. This does get a little fuzzy when we > >> > consider > >> > >> >> cases > >> > >> >> > > where > >> > >> >> > > >>> brokers are on different software versions and could be > >> > >> generating > >> > >> >> a > >> > >> >> > > >>> downgrade snapshot for version X, but using different > >> > versions > >> > >> of > >> > >> >> the > >> > >> >> > > >>> code. > >> > >> >> > > >>> It might be safer to let the controller generate the > >> > snapshot so > >> > >> >> each > >> > >> >> > > >>> broker (regardless of software version) gets the same > >> > records. > >> > >> >> > However, > >> > >> >> > > >>> for > >> > >> >> > > >>> upgrades (or downgrades) we expect the whole cluster to > be > >> > >> running > >> > >> >> > the > >> > >> >> > > >>> same > >> > >> >> > > >>> software version before triggering the metadata.version > >> > change, > >> > >> so > >> > >> >> > > perhaps > >> > >> >> > > >>> this isn't a likely scenario. Thoughts? > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> 3. Max metadata version > >> > >> >> > > >>> > >For the first release that supports > metadata.version, we > >> > can > >> > >> >> > simply > >> > >> >> > > >>> > initialize metadata.version with the current (and > only) > >> > >> version. > >> > >> >> > For > >> > >> >> > > >>> future > >> > >> >> > > >>> > releases, we will need a mechanism to bootstrap a > >> > particular > >> > >> >> > version. > >> > >> >> > > >>> This > >> > >> >> > > >>> > could be done using the meta.properties file or some > >> > similar > >> > >> >> > > mechanism. > >> > >> >> > > >>> The > >> > >> >> > > >>> > reason we need the allow for a specific initial > version > >> is > >> > to > >> > >> >> > support > >> > >> >> > > >>> the > >> > >> >> > > >>> > use case of starting a Kafka cluster at version X > with an > >> > >> older > >> > >> >> > > >>> > metadata.version. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> I assume that the Active Controller will learn the > metadata > >> > >> version > >> > >> >> > of > >> > >> >> > > >>> > the broker through the BrokerRegistrationRequest. How > >> will > >> > the > >> > >> >> > Active > >> > >> >> > > >>> > Controller learn about the max metadata version of the > >> > >> inactive > >> > >> >> > > >>> > controller nodes? We currently don't send a > registration > >> > >> request > >> > >> >> > from > >> > >> >> > > >>> > the inactive controller to the active controller. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> This came up during the design, but I neglected to add > it > >> to > >> > the > >> > >> >> KIP. > >> > >> >> > > We > >> > >> >> > > >>> will need a mechanism for determining the supported > >> features > >> > of > >> > >> >> each > >> > >> >> > > >>> controller similar to how brokers use > >> > BrokerRegistrationRequest. > >> > >> >> > > Perhaps > >> > >> >> > > >>> controllers could write a FeatureLevelRecord (or > similar) > >> to > >> > the > >> > >> >> > > metadata > >> > >> >> > > >>> log indicating their supported version. WDYT? > >> > >> >> > > >>> > >> > >> >> > > >>> Why do you need to bootstrap a particular version? Isn't > >> the > >> > >> intent > >> > >> >> > > >>> > that the broker will learn the active metadata > version by > >> > >> reading > >> > >> >> > the > >> > >> >> > > >>> > metadata before unfencing? > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> This bootstrapping is needed for when a KRaft cluster is > >> > first > >> > >> >> > > started. If > >> > >> >> > > >>> we don't have this mechanism, the cluster can't really > do > >> > >> anything > >> > >> >> > > until > >> > >> >> > > >>> the operator finalizes the metadata.version with the > tool. > >> > The > >> > >> >> > > >>> bootstrapping will be done by the controller and the > >> brokers > >> > >> will > >> > >> >> see > >> > >> >> > > this > >> > >> >> > > >>> version as a record (like you say). I'll add some text > to > >> > >> clarify > >> > >> >> > this. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> 4. Reject Registration - This is related to the bullet > >> point > >> > >> above. > >> > >> >> > > >>> > What will be the behavior of the active controller if > the > >> > >> broker > >> > >> >> > > sends > >> > >> >> > > >>> > a metadata version that is not compatible with the > >> cluster > >> > >> wide > >> > >> >> > > >>> > metadata version? > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> If a broker starts up with a lower supported version > range > >> > than > >> > >> the > >> > >> >> > > >>> current > >> > >> >> > > >>> cluster metadata.version, it should log an error and > >> > shutdown. > >> > >> This > >> > >> >> > is > >> > >> >> > > in > >> > >> >> > > >>> line with KIP-584. > >> > >> >> > > >>> > >> > >> >> > > >>> 5. Discover upgrade > >> > >> >> > > >>> > > This snapshot will be a convenient way to let broker > >> and > >> > >> >> > controller > >> > >> >> > > >>> > components rebuild their entire in-memory state > following > >> > an > >> > >> >> > upgrade. > >> > >> >> > > >>> > Can we rely on the presence of the FeatureLevelRecord > for > >> > the > >> > >> >> > > metadata > >> > >> >> > > >>> > version for this functionality? If so, it avoids > having > >> to > >> > >> reload > >> > >> >> > the > >> > >> >> > > >>> > snapshot. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> For upgrades, yes probably since we won't need to > "rewrite" > >> > any > >> > >> >> > > records in > >> > >> >> > > >>> this case. For downgrades, we will need to generate the > >> > snapshot > >> > >> >> and > >> > >> >> > > >>> reload > >> > >> >> > > >>> everything. > >> > >> >> > > >>> > >> > >> >> > > >>> 6. Metadata version specification > >> > >> >> > > >>> > > V4(version=4, isBackwardsCompatible=false, > >> > description="New > >> > >> >> > > metadata > >> > >> >> > > >>> > record type Bar"), > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> Very cool. Do you have plans to generate Apache Kafka > HTML > >> > >> >> > > >>> > documentation for this information? Would be helpful > to > >> > >> display > >> > >> >> > this > >> > >> >> > > >>> > information to the user using the kafka-features.sh > and > >> > >> feature > >> > >> >> > RPC? > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> Hm good idea :) I'll add a brief section on > documentation. > >> > This > >> > >> >> would > >> > >> >> > > >>> certainly be very useful > >> > >> >> > > >>> > >> > >> >> > > >>> 7.Downgrade records > >> > >> >> > > >>> > I think we should explicitly mention that the > downgrade > >> > >> process > >> > >> >> > will > >> > >> >> > > >>> > downgrade both metadata records and controller > records. > >> In > >> > >> >> KIP-630 > >> > >> >> > we > >> > >> >> > > >>> > introduced two control records for snapshots. > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> Yes, good call. Let me re-read that KIP and include some > >> > >> details. > >> > >> >> > > >>> > >> > >> >> > > >>> Thanks again for the comments! > >> > >> >> > > >>> -David > >> > >> >> > > >>> > >> > >> >> > > >>> > >> > >> >> > > >>> On Wed, Sep 29, 2021 at 5:09 PM José Armando García > Sancio > >> > >> >> > > >>> <jsan...@confluent.io.invalid> wrote: > >> > >> >> > > >>> > >> > >> >> > > >>> > One more comment. > >> > >> >> > > >>> > > >> > >> >> > > >>> > 7.Downgrade records > >> > >> >> > > >>> > I think we should explicitly mention that the > downgrade > >> > >> process > >> > >> >> > will > >> > >> >> > > >>> > downgrade both metadata records and controller > records. > >> In > >> > >> >> KIP-630 > >> > >> >> > we > >> > >> >> > > >>> > introduced two control records for snapshots. > >> > >> >> > > >>> > > >> > >> >> > > >>> > >> > >> >> > > >> > >> > >> >> > > > >> > >> >> > > >> > >> >> > >> > >> >> > >> > >> >> -- > >> > >> >> -David > >> > >> >> > >> > >> > >> > > >> >