Hi,

Given that 5.0 is likely 2 years away and we won't have a branch to make
these changes for a while, is it premature to be discussing KIPs such as
this one? Perhaps we should wait and see how the logging landscape evolves
to decide if we want to go with slf4j 2 or something else.

Ismael

On Thu, Apr 10, 2025 at 3:05 AM TengYao Chi <kiting...@gmail.com> wrote:

> Hello guys,
>
> I want to bump this vote thread manually.
> Thanks for your attention.
>
> Best,
> TengYao
>
> Stig Rohde Døssing <stigdoess...@gmail.com> 於 2025年3月24日 週一 上午3:58寫道:
>
> > Thanks TengYao,
> >
> > I note that the KIP's scope has shrunk a bit, and the goal now is only to
> > upgrade slf4j to make it easy for users to replace log4j2 with another
> > slf4j binding, but Kafka will only ship with log4j2 and not alternatives,
> > so people who want to use something else will have to bring their own
> jars.
> >
> > +1 (non-binding, not a committer) for that plan
> >
> > Den søn. 23. mar. 2025 kl. 12.13 skrev TengYao Chi <kiting...@gmail.com
> >:
> >
> > > Hi everyone
> > >
> > > I have updated the content of KIP.
> > > I want to highlight that although we set log4j2 as the default
> > server-side
> > > logging framework we couldn't change its scope to implementation in
> > > `build.gradle`.
> > > This will lead the downstream projects to encounter dependency
> conflicts.
> > >
> > > Please take a look and share your feedback.
> > >
> > > Best,
> > > TengYao
> > >
> > > TengYao Chi <kiting...@gmail.com> 於 2025年3月23日 週日 下午2:23寫道:
> > >
> > > > Hi Stig
> > > >
> > > > Sorry for the late reply, and thanks for your question. 😀
> > > >
> > > > The title "Upgrade slf4j to 2.x" represents the core change enabling
> > > > improved logging backend selection.
> > > > The fundamental change is the SLF4J upgrade, which brings the new
> > > provider
> > > > selection mechanism (`-Dslf4j.provider`) as a key feature.
> > > > Given that, I think the current title reflects the primary technical
> > > > change, while the KIP details explain the resulting benefits and
> > > > implementation approach.
> > > >
> > > > Best,
> > > > TengYao
> > > >
> > > >
> > > > Stig Rohde Døssing <stigdoess...@gmail.com> 於 2025年3月21日 週五
> 下午11:46寫道:
> > > >
> > > >> The title of the KIP seems a little odd, because if I understand
> > > >> correctly,
> > > >> the main change you want to make is to bundle multiple logging
> > backends
> > > >> with Kafka and make them selectable via a system property, and
> > upgrading
> > > >> sfl4j is a means to achieve that, not the goal itself?
> > > >>
> > > >> Den fre. 21. mar. 2025 kl. 12.18 skrev Chia-Ping Tsai <
> > > chia7...@gmail.com
> > > >> >:
> > > >>
> > > >> > hi Teng
> > > >> >
> > > >> > > The KIP will document that log4j2 is the only officially
> supported
> > > >> >    server-side logging framework, and we will expose its
> > configuration
> > > >> file
> > > >> > to
> > > >> >    users.
> > > >> >
> > > >> > on the server-side, we should keep current scope - compileOnly and
> > > >> > releaseOnly - Otherwise, downstream projects could encounter
> > > dependency
> > > >> > conflicts [0]
> > > >> >
> > > >> > >  I will revise the motivation section of the KIP to emphasize
> that
> > > the
> > > >> >
> > > >> > Please include the following description.
> > > >> >
> > > >> > "The rationale for this KIP is that upgrading SLF4J necessitates
> > > >> > corresponding provider upgrades, which constitutes a breaking
> > change."
> > > >> >
> > > >> > Also, we must upgrade the Log4j2 dependency based on SLF4J 2
> (i.e.,
> > > >> > log4j-slf4j-impl to log4j-slf4j2-impl) in 5.0 if we upgrade to
> > slf4j2
> > > >> >
> > > >> > [0]
> > > https://github.com/apache/kafka/pull/17373#issuecomment-2577813317
> > > >> >
> > > >> > Best,
> > > >> >
> > > >> > Chia-Ping
> > > >> >
> > > >> >
> > > >> > TengYao Chi <kiting...@gmail.com> 於 2025年3月21日 週五 下午6:52寫道:
> > > >> >
> > > >> > > Hello everyone,
> > > >> > >
> > > >> > > Sorry for the late reply.
> > > >> > > Based on the previous discussion, I would like to conclude with
> > the
> > > >> > > following points:
> > > >> > >
> > > >> > >    1. The upgrade to slf4j2 should be postponed to Kafka 5.0 due
> > to
> > > >> > >    compatibility issues.
> > > >> > >    2. I will revise the motivation section of the KIP to
> emphasize
> > > >> that
> > > >> > the
> > > >> > >    key benefit is allowing users to select logging backends
> > through
> > > >> > >    configuration rather than modifying JAR files.
> > > >> > >    3. After the slf4j upgrade, users will be able to use the
> > > >> > >    `-Dslf4j.provider` system property to configure their
> preferred
> > > >> > logging
> > > >> > >    backend.
> > > >> > >    4. The KIP will document that log4j2 is the only officially
> > > >> supported
> > > >> > >    server-side logging framework, and we will expose its
> > > configuration
> > > >> > > file to
> > > >> > >    users.
> > > >> > >    To avoid breaking downstream compatibility, we will not bind
> > the
> > > >> > client
> > > >> > >    side to any specific logging framework. Users will need to
> > manage
> > > >> > their
> > > >> > > own
> > > >> > >    logging libraries, but they can utilize the
> `-Dslf4j.provider`
> > > >> > property
> > > >> > >    once slf4j is upgraded.
> > > >> > >    5. We have rejected alternatives that involve warnings and
> > > >> classpath
> > > >> > >    ordering as they do not provide a solid solution to
> > compatibility
> > > >> > > issues.
> > > >> > >
> > > >> > > Does this summary make sense?
> > > >> > >
> > > >> > > Best,
> > > >> > > TengYao
> > > >> > >
> > > >> > > Ismael Juma <m...@ismaeljuma.com> 於 2025年3月21日 週五 上午9:32寫道:
> > > >> > >
> > > >> > > > A solution that involves a warning and classpath ordering
> > doesn't
> > > >> meet
> > > >> > > the
> > > >> > > > bar for me. Good clarification though.
> > > >> > > >
> > > >> > > > Ismael
> > > >> > > >
> > > >> > > > On Thu, Mar 20, 2025 at 8:37 AM Farid Zakaria
> > > >> > > > <fzaka...@confluent.io.invalid>
> > > >> > > > wrote:
> > > >> > > >
> > > >> > > > > AFAIR SLF4J you don't have to remove the other backends;
> > merely
> > > >> make
> > > >> > > > > sure yours is first on the CLASSPATH list :P
> > > >> > > > > (SLF4J pre 2.0 would always emit a warning that it found 2+
> > > >> > > > StaticBinders)
> > > >> > > > >
> > > >> > > > > Interestingly, you could still whatever backend (i.e. Log4J)
> > and
> > > >> pipe
> > > >> > > > > it through to another backend via another appender.
> > > >> > > > > This is what SLF4J refers to bridges -- although you have to
> > be
> > > >> sure
> > > >> > > > > not to create a circular loop.
> > > >> > > > >
> > > >> > > > > Then there is something also general like syslog.
> > > >> > > > >
> > > >> > > > > On Thu, Mar 20, 2025 at 1:15 AM Chia-Ping Tsai <
> > > >> chia7...@gmail.com>
> > > >> > > > wrote:
> > > >> > > > > >
> > > >> > > > > > hi Ismael
> > > >> > > > > >
> > > >> > > > > > thanks for all your response.
> > > >> > > > > >
> > > >> > > > > > > All that said, I am not actually sure we can do what I
> > > >> described
> > > >> > > > above
> > > >> > > > > > while maintaining the compatibility required by a minor
> > > release.
> > > >> > > > > >
> > > >> > > > > > Excuse me, are your concerns related to version matching,
> as
> > > >> > > discussed
> > > >> > > > in
> > > >> > > > > > [0]? If so, I concur that this represents a compatibility
> > > issue,
> > > >> > and
> > > >> > > > the
> > > >> > > > > > target version for this change should be 5.0.
> Additionally,
> > > >> there
> > > >> > > was a
> > > >> > > > > > related discussion previously documented in [1]. While we
> > have
> > > >> not
> > > >> > > > > strictly
> > > >> > > > > > enforced version matching during prior SLF4J updates, this
> > KIP
> > > >> > > provides
> > > >> > > > > an
> > > >> > > > > > opportunity to establish guidelines for upgrading sl4fj
> that
> > > >> have
> > > >> > > > direct
> > > >> > > > > > compatibility implications.
> > > >> > > > > >
> > > >> > > > > > [0] https://www.slf4j.org/faq.html#compatibility
> > > >> > > > > > [1]
> > > >> > >
> https://github.com/apache/kafka/pull/16324#discussion_r1644671854
> > > >> > > > > >
> > > >> > > > > > To Teng
> > > >> > > > > >
> > > >> > > > > > Could you please revise the KIP according to following
> > > benefit?
> > > >> > > > > >
> > > >> > > > > > > The key benefit of this KIP is that you can add new
> > logging
> > > >> > > backends
> > > >> > > > > and
> > > >> > > > > > select it via a config. This is how most pluggable things
> > > work.
> > > >> But
> > > >> > > it
> > > >> > > > is
> > > >> > > > > > *not* how slf4j 1.x works. slf4j 1.x requires you to
> > *remove*
> > > >> the
> > > >> > > > default
> > > >> > > > > > logging library picked by the project as well. That's much
> > > more
> > > >> > > > > intrusive.
> > > >> > > > > >
> > > >> > > > > > Best,
> > > >> > > > > > Chia-Ping
> > > >> > > > > >
> > > >> > > > > > Ismael Juma <m...@ismaeljuma.com> 於 2025年3月20日 週四 上午8:10寫道:
> > > >> > > > > >
> > > >> > > > > > > Hi Chia-Ping,
> > > >> > > > > > >
> > > >> > > > > > > I don't think we're in the business of shipping multiple
> > > >> logging
> > > >> > > > > libraries.
> > > >> > > > > > > Here's my take:
> > > >> > > > > > >
> > > >> > > > > > > 1. We should pick one logging library for
> > services/servers,
> > > >> ship
> > > >> > it
> > > >> > > > and
> > > >> > > > > > > include a configuration file for it.
> > > >> > > > > > > 2. For clients, we leave it to the users to select the
> > > logging
> > > >> > > > library
> > > >> > > > > -
> > > >> > > > > > > clients run alongside applications and it's desirable to
> > use
> > > >> the
> > > >> > > same
> > > >> > > > > > > logging library for both (if we were starting from
> > scratch,
> > > we
> > > >> > may
> > > >> > > > have
> > > >> > > > > > > decided to also include our default logging library for
> > > >> clients
> > > >> > as
> > > >> > > > > well,
> > > >> > > > > > > but it's hard to make that change now).
> > > >> > > > > > > 3. For the cases where users want to use a different
> > logging
> > > >> > > library
> > > >> > > > > for
> > > >> > > > > > > services/servers (perhaps because they have standardized
> > on
> > > a
> > > >> > > > different
> > > >> > > > > > > logging library), they would have to add the additional
> > jar
> > > to
> > > >> > the
> > > >> > > > > > > classpath and change the relevant logging config. This
> is
> > no
> > > >> > > > different
> > > >> > > > > than
> > > >> > > > > > > adding a different authorizer or any other pluggable
> > > >> component.
> > > >> > > > > > >
> > > >> > > > > > > The key benefit of this KIP is that you can add new
> > logging
> > > >> > > backends
> > > >> > > > > and
> > > >> > > > > > > select it via a config. This is how most pluggable
> things
> > > >> work.
> > > >> > But
> > > >> > > > it
> > > >> > > > > is
> > > >> > > > > > > *not* how slf4j 1.x works. slf4j 1.x requires you to
> > > *remove*
> > > >> the
> > > >> > > > > default
> > > >> > > > > > > logging library picked by the project as well. That's
> much
> > > >> more
> > > >> > > > > intrusive.
> > > >> > > > > > >
> > > >> > > > > > > All that said, I am not actually sure we can do what I
> > > >> described
> > > >> > > > above
> > > >> > > > > > > while maintaining the compatibility required by a minor
> > > >> release.
> > > >> > > > > > >
> > > >> > > > > > > Ismael
> > > >> > > > > > >
> > > >> > > > > > > On Wed, Mar 19, 2025, 2:03 PM Chia-Ping Tsai <
> > > >> chia7...@gmail.com
> > > >> > >
> > > >> > > > > wrote:
> > > >> > > > > > >
> > > >> > > > > > > > hi Ismael
> > > >> > > > > > > >
> > > >> > > > > > > > > but they must also add whichever logging library
> they
> > > >> want to
> > > >> > > > use.
> > > >> > > > > > > >
> > > >> > > > > > > > If users are required to modify JAR files to alter the
> > > SLF4J
> > > >> > > > > provider,
> > > >> > > > > > > the
> > > >> > > > > > > > value of this KIP is significantly diminished. I
> believe
> > > the
> > > >> > > > primary
> > > >> > > > > > > > benefit of this KIP lies in enabling users to
> configure
> > a
> > > >> > system
> > > >> > > > > property
> > > >> > > > > > > > for SLF4J provider changes without JAR modifications.
> > > >> > > Furthermore,
> > > >> > > > by
> > > >> > > > > > > > managing all SLF4J and provider JARs within Kafka, we
> > can
> > > >> > ensure
> > > >> > > > > SLF4J
> > > >> > > > > > > > version updates without compatibility concerns, as we
> > can
> > > >> > > guarantee
> > > >> > > > > > > > provider JAR consistency with the SLF4J version in the
> > > >> > > > distribution.
> > > >> > > > > > > >
> > > >> > > > > > > > Best,
> > > >> > > > > > > > Chia-Ping
> > > >> > > > > > > >
> > > >> > > > > > > > Ismael Juma <m...@ismaeljuma.com> 於 2025年3月19日 週三
> > > 下午12:00寫道:
> > > >> > > > > > > >
> > > >> > > > > > > > > Hi TengYao,
> > > >> > > > > > > > >
> > > >> > > > > > > > > It's a bit difficult to review the KIP. I don't
> follow
> > > >> most
> > > >> > of
> > > >> > > > the
> > > >> > > > > > > > > motivation. The only one that I follow is:
> > > >> > > > > > > > >
> > > >> > > > > > > > > "Our current build configuration employs fragile
> > > >> dependency
> > > >> > > > > management
> > > >> > > > > > > > > tricks to handle SLF4J backends. We can eliminate
> > these
> > > >> > brittle
> > > >> > > > > build
> > > >> > > > > > > > > mechanisms by transitioning to explicit provider
> > > >> dependencies
> > > >> > > > after
> > > >> > > > > > > > > upgrading to 2.0."
> > > >> > > > > > > > >
> > > >> > > > > > > > > Additionally, I don't think we should do the
> > following:
> > > >> > > > > > > > >
> > > >> > > > > > > > > "Add other popular slf4j backend binding provider
> > > >> > > dependencies."
> > > >> > > > > > > > >
> > > >> > > > > > > > > A reasonable approach, in my opinion, would be:
> > > >> > > > > > > > >
> > > >> > > > > > > > > 1. Include the log4j2 dependency with the server
> > modules
> > > >> and
> > > >> > > not
> > > >> > > > > > > include
> > > >> > > > > > > > > them with the client modules.
> > > >> > > > > > > > > 2. Automatically configure the log4j2 dependency for
> > the
> > > >> > server
> > > >> > > > > > > modules.
> > > >> > > > > > > > > Users can override them via the system property, but
> > > they
> > > >> > must
> > > >> > > > > also add
> > > >> > > > > > > > > whichever logging library they want to use.
> > > >> > > > > > > > > 3. Somehow configure slf4j 2.x to work like 1.x out
> of
> > > the
> > > >> > box
> > > >> > > > for
> > > >> > > > > the
> > > >> > > > > > > > > client module (for compatibility reasons).
> > > >> > > > > > > > >
> > > >> > > > > > > > > But I don't know if `3` is possible. If `3` is not
> > > >> possible,
> > > >> > I
> > > >> > > > > don't
> > > >> > > > > > > see
> > > >> > > > > > > > > how we can make this a compatible change.
> > > >> > > > > > > > >
> > > >> > > > > > > > > Ismael
> > > >> > > > > > > > >
> > > >> > > > > > > > > On Tue, Mar 18, 2025 at 7:41 PM TengYao Chi <
> > > >> > > kiting...@gmail.com
> > > >> > > > >
> > > >> > > > > > > wrote:
> > > >> > > > > > > > >
> > > >> > > > > > > > > > Hello everyone,
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > I want to bump this thread manually.
> > > >> > > > > > > > > > Any feedback or vote would be appreciated.
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > Best,
> > > >> > > > > > > > > > TengYao
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > TengYao Chi <kiting...@gmail.com> 於 2025年3月10日 週一
> > > >> > 上午11:47寫道:
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > > Hello guys,
> > > >> > > > > > > > > > > I would like to remind you in the vote thread
> that
> > > the
> > > >> > KIP
> > > >> > > > has
> > > >> > > > > been
> > > >> > > > > > > > > > > updated, and I apologize for repeating it.
> > > >> > > > > > > > > > > I have taken over this KIP from Muralidhar.
> > > >> > > > > > > > > > > Since the original content is outdated as the
> > > logging
> > > >> > > > > framework has
> > > >> > > > > > > > > been
> > > >> > > > > > > > > > > widely changed, I have updated the content of
> the
> > > KIP.
> > > >> > > > > > > > > > > Please take a look and share your thoughts.
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Best Regards,
> > > >> > > > > > > > > > > TengYao
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Muralidhar Basani <muralidhar.bas...@aiven.io
> > > .invalid>
> > > >> 於
> > > >> > > > > > > 2024年9月24日
> > > >> > > > > > > > 週二
> > > >> > > > > > > > > > > 上午5:09寫道:
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > >> Hi,
> > > >> > > > > > > > > > >>
> > > >> > > > > > > > > > >> I wanted to gently follow up on this thread in
> > case
> > > >> > anyone
> > > >> > > > > has any
> > > >> > > > > > > > > > >> thoughts
> > > >> > > > > > > > > > >> or would like to take a look.
> > > >> > > > > > > > > > >>
> > > >> > > > > > > > > > >> Thanks,
> > > >> > > > > > > > > > >> Murali
> > > >> > > > > > > > > > >>
> > > >> > > > > > > > > > >> On Mon, Sep 16, 2024 at 10:23 AM Muralidhar
> > Basani
> > > <
> > > >> > > > > > > > > > >> muralidhar.bas...@aiven.io> wrote:
> > > >> > > > > > > > > > >>
> > > >> > > > > > > > > > >> > Thanks Chia.
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >> > I have updated KIP with this quote, in the
> > > >> migration
> > > >> > > plan
> > > >> > > > > > > section.
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >> > Thanks,
> > > >> > > > > > > > > > >> > Murali
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >> > On Sun, Sep 15, 2024 at 3:30 PM Chia-Ping
> Tsai
> > <
> > > >> > > > > > > > chia7...@gmail.com>
> > > >> > > > > > > > > > >> wrote:
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >> >>
> > > >> > > > > > > > > > >> >> > Muralidhar Basani <
> > muralidhar.bas...@aiven.io
> > > >> > > .invalid>
> > > >> > > > 於
> > > >> > > > > > > > > > 2024年9月15日
> > > >> > > > > > > > > > >> >> 晚上9:02 寫道:
> > > >> > > > > > > > > > >> >> >
> > > >> > > > > > > > > > >> >> > With this, I think, users don't have to
> make
> > > any
> > > >> > > > explicit
> > > >> > > > > > > > changes
> > > >> > > > > > > > > > in
> > > >> > > > > > > > > > >> >> their
> > > >> > > > > > > > > > >> >> > code, if their provider is reload4j. And
> if
> > > >> it's a
> > > >> > > > > different
> > > >> > > > > > > > > > provider
> > > >> > > > > > > > > > >> >> (like
> > > >> > > > > > > > > > >> >> > logback, log4j), they would have to
> upgrade
> > > >> that to
> > > >> > > > > match it
> > > >> > > > > > > > with
> > > >> > > > > > > > > > >> slf4j.
> > > >> > > > > > > > > > >> >>
> > > >> > > > > > > > > > >> >> If upgrading the matched provider is the
> only
> > > >> > explicit
> > > >> > > > > change
> > > >> > > > > > > and
> > > >> > > > > > > > > we
> > > >> > > > > > > > > > >> >> expect users have responsibility to keep
> > > >> consistent
> > > >> > > > version
> > > >> > > > > > > when
> > > >> > > > > > > > > > using
> > > >> > > > > > > > > > >> >> other providers , could we write it down to
> > the
> > > >> KIP?
> > > >> > > > > > > > > > >> >>
> > > >> > > > > > > > > > >> >> That means we will update slf4j without KIP
> in
> > > the
> > > >> > > future
> > > >> > > > > > > except
> > > >> > > > > > > > > for
> > > >> > > > > > > > > > >> >> specific reason.
> > > >> > > > > > > > > > >> >>
> > > >> > > > > > > > > > >> >> Best,
> > > >> > > > > > > > > > >> >> Chia-Ping
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >> >
> > > >> > > > > > > > > > >>
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> > > >> > >
> > > >> >
> > > >>
> > > >
> > >
> >
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