Hello Lucas!

I already created a new RC and was just about to write the vote email
- are these critical? Is it possible that you cherry-pick them on 4.2
with the goal that if 4.2.0-rc2 is cut they make it in there, but for
now we exclude them from 4.2.0-rc1? Or are they critical enough that
they would justify creating 4.2.0-rc2 on their own?

Best,
Christo

On Mon, 19 Jan 2026 at 14:28, Lucas Brutschy <[email protected]> wrote:
>
> Hey Christo,
>
> could we include fixes for two usability issues in the new RC? They
> are minor low-risk changes, but it would be good to include them. Let
> me know, so I can cherry-pick them today.
>
> - 
> https://github.com/apache/kafka/commit/7fa5121a172e4ac0248c15e73d5833dcec9bb7d8
> - 
> https://github.com/apache/kafka/commit/c552631801f709ff7d1090b99dd5f0053d5c08ce
>
> Cheers,
> Lucas
>
> On Mon, Jan 19, 2026 at 11:34 AM Christo Lolov <[email protected]> wrote:
> >
> > Heya David,
> >
> > Yes, it makes sense for these to be cherry-picked, I will be creating
> > RC1 later today, so I will cherry-pick them beforehand, thanks for
> > bringing these to my attention!
> >
> > I am now closing the voting thread for RC0!
> >
> > Best,
> > Christo
> >
> > On Fri, 16 Jan 2026 at 13:39, David Jacot via dev <[email protected]> 
> > wrote:
> > >
> > > Hi Christo,
> > >
> > > If we cut a new RC, I wonder if we could include the fixes for
> > > https://issues.apache.org/jira/browse/KAFKA-19233. They are all very small
> > > changes (with a lot of tests). It may be helpful for Queues and Streams to
> > > go GA. What do you think?
> > >
> > > Best,
> > > Davud
> > >
> > > On Fri, Jan 16, 2026 at 12:23 PM Christo Lolov <[email protected]>
> > > wrote:
> > >
> > > > Heya Paolo,
> > > >
> > > > Thanks for catching this and providing a fix! It makes sense to me
> > > > that since this is part of Kafka Connect's REST API it is public and
> > > > therefore we can't change the output without a corresponding KIP. I
> > > > have reviewed the PR and I am happy to cherry-pick it once it has made
> > > > it into trunk and include it in RC1.
> > > >
> > > > Best,
> > > > Christo
> > > >
> > > > On Fri, 16 Jan 2026 at 10:33, Paolo Patierno <[email protected]>
> > > > wrote:
> > > > >
> > > > > FYI I opened https://issues.apache.org/jira/browse/KAFKA-20076 and 
> > > > > also
> > > > a
> > > > > corresponding PR to fix the issue here
> > > > > https://github.com/apache/kafka/pull/21318
> > > > > It's against trunk but I think we should (if/when approved) 
> > > > > cherry-pick
> > > > to
> > > > > 4.2.0.
> > > > >
> > > > > Thanks,
> > > > > Paolo
> > > > >
> > > > > On Thu, 15 Jan 2026 at 17:01, Paolo Patierno 
> > > > > <[email protected]>
> > > > > wrote:
> > > > >
> > > > > > Hello,
> > > > > > I think I have found a regression.
> > > > > > When running Kafka Connect and submitting an HTTP GET request to the
> > > > > > /connector-plugins endpoint, the JSON serialized "type" filed in the
> > > > body
> > > > > > response is now uppercase instead of being lowercase as in the past.
> > > > > > Following a comparison between Apache Kafka 4.1 ...
> > > > > >
> > > > > >
> > > > > >
> > > > [{"class":"org.apache.kafka.connect.mirror.MirrorCheckpointConnector","type":"source","version":"4.1.1"},{"class":"org.apache.kafka.connect.mirror.MirrorHeartbeatConnector","type":"source","version":"4.1.1"},{"class":"org.apache.kafka.connect.mirror.MirrorSourceConnector","type":"source","version":"4.1.1"}]
> > > > > >
> > > > > > ... and the current Apache Kafka 4.2 RC0
> > > > > >
> > > > > >
> > > > > >
> > > > [{"class":"org.apache.kafka.connect.mirror.MirrorCheckpointConnector","type":"SOURCE","version":"4.2.0"},{"class":"org.apache.kafka.connect.mirror.MirrorHeartbeatConnector","type":"SOURCE","version":"4.2.0"},{"class":"org.apache.kafka.connect.mirror.MirrorSourceConnector","type":"SOURCE","version":"4.2.0"}]
> > > > > >
> > > > > > As you can see it's "source" vs "SOURCE". I had same result with
> > > > "sink" vs
> > > > > > "SINK".
> > > > > >
> > > > > > I think this is due to the last change from converting the 
> > > > > > PluginInfo
> > > > from
> > > > > > being a class to a record which had an impact together with the JSON
> > > > > > serialization.
> > > > > > When it was a class, a dedicated type.toString() was used which
> > > > explicitly
> > > > > > does a lower case transformation.
> > > > > > As a record, the "type" field is directly serialized by JSON by 
> > > > > > using
> > > > the
> > > > > > enum values from PluginType which are all uppercase of course.
> > > > > > It means that this issue affects all the other values as well the 
> > > > > > way
> > > > they
> > > > > > are serialized (not just SINK, SOURCE but also CONVERTER,
> > > > TRANSFORMATION,
> > > > > > and so on).
> > > > > >
> > > > > > If you like I could provide a contribution for that.
> > > > > >
> > > > > > Thanks,
> > > > > > Paolo.
> > > > > >
> > > > > > On Tue, 13 Jan 2026 at 17:04, Christo Lolov <[email protected]>
> > > > > > wrote:
> > > > > >
> > > > > >> Hello Kafka users, developers and client-developers,
> > > > > >>
> > > > > >> This is the RC0 candidate for release of Apache Kafka 4.2.0.
> > > > > >>
> > > > > >> This release has many exciting changes such as Kafka Queues being
> > > > > >> marked as production-ready, dead letter queues in Kafka Streams, a
> > > > > >> preview of the new Kafka Streams rebalance protocol, improved
> > > > > >> consistency across Kafka CLI arguments and metrics!
> > > > > >>
> > > > > >> I will raise a PR with a new blog post to the kafka-site 
> > > > > >> repository in
> > > > > >> the next 24 hours and share the link as a reply to this thread.
> > > > > >>
> > > > > >> Release notes for the 4.2.0 release:
> > > > > >>
> > > > https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc0/RELEASE_NOTES.html
> > > > > >>
> > > > > >> *** Please download, test and vote by Wednesday, January 21, 10am 
> > > > > >> UTC
> > > > > >>
> > > > > >> Kafka's KEYS file containing PGP keys we use to sign the release:
> > > > > >> https://kafka.apache.org/KEYS
> > > > > >>
> > > > > >> * Release artifacts to be voted upon (source and binary):
> > > > > >> https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc0/
> > > > > >>
> > > > > >> * Docker release artifacts to be voted upon:
> > > > > >> apache/kafka:4.2.0-rc0
> > > > > >> apache/kafka-native:4.2.0-rc0
> > > > > >>
> > > > > >> * Maven artifacts to be voted upon:
> > > > > >>
> > > > https://repository.apache.org/content/groups/staging/org/apache/kafka/
> > > > > >>
> > > > > >> * Javadoc:
> > > > > >>
> > > > https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc0/javadoc/index.html
> > > > > >>
> > > > > >> * Tag to be voted upon (off 4.2 branch) is the 4.2.0 tag:
> > > > > >> https://github.com/apache/kafka/releases/tag/4.2.0-rc0
> > > > > >>
> > > > > >> * Documentation:
> > > > > >> I will raise a PR with the changes to the kafka-site repository in 
> > > > > >> the
> > > > > >> next 24 hours and share the link as a reply to this thread.
> > > > > >>
> > > > > >> * Protocol:
> > > > > >> I will raise a PR with the changes to the kafka-site repository in 
> > > > > >> the
> > > > > >> next 24 hours and share the link as a reply to this thread.
> > > > > >>
> > > > > >> * Successful CI builds for the 4.2 branch:
> > > > > >> Unit/integration tests:
> > > > > >>
> > > > https://github.com/apache/kafka/actions/runs/20953445348/job/60245258542
> > > > > >> System tests: My environment needs to be recreated before I can 
> > > > > >> share
> > > > > >> results from my end, so any results shared by voters would be 
> > > > > >> greatly
> > > > > >> appreciated!
> > > > > >>
> > > > > >> * Successful Docker Image Github Actions Pipeline for 4.2 branch:
> > > > > >> Docker Build Test Pipeline (JVM):
> > > > > >> https://github.com/apache/kafka/actions/runs/20962291986
> > > > > >> Docker Build Test Pipeline (Native):
> > > > > >> https://github.com/apache/kafka/actions/runs/20958037429
> > > > > >>
> > > > > >> Note - when I run the quickstart against the JVM Docker image I 
> > > > > >> need
> > > > > >> to specify the process.roles. I do not seem to need to specify the
> > > > > >> process.roles if I run the 4.1.1 image. I will run this once again
> > > > > >> tomorrow in another clean environment, but if somebody else can
> > > > > >> confirm/deny whether they can reproduce this beforehand this would
> > > > > >> also be greatly appreciated!
> > > > > >>
> > > > > >> Thanks,
> > > > > >> Christo
> > > > > >>
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Paolo Patierno
> > > > > >
> > > > > > *Senior Principal Software Engineer @ IBM**CNCF Ambassador*
> > > > > >
> > > > > > Twitter : @ppatierno <http://twitter.com/ppatierno>
> > > > > > Linkedin : paolopatierno <http://it.linkedin.com/in/paolopatierno>
> > > > > > GitHub : ppatierno <https://github.com/ppatierno>
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Paolo Patierno
> > > > >
> > > > > *Senior Principal Software Engineer @ IBM**CNCF Ambassador*
> > > > >
> > > > > Twitter : @ppatierno <http://twitter.com/ppatierno>
> > > > > Linkedin : paolopatierno <http://it.linkedin.com/in/paolopatierno>
> > > > > GitHub : ppatierno <https://github.com/ppatierno>
> > > >
> >
> > --
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