Hi Chris and Luke,
Thank you very much for your feedback.
I have addressed some of the suggestions and would like to clarify a few
things on the others:
> 1) The current logic for syncing topic configs in MM2 is basically
fire-and-forget; all we do is log a warning message [1] if an attempt
fails. When "use.incremental.alter.configs" is set to "requested", we'll
need to know whether attempts using the incremental API succeed or not, and
then adjust our behavior accordingly. Will the plan here be to block on the
success/failure of the first request before sending any more, or will we
just switch over to the legacy API as soon as any request fails due to
targeting an incompatible broker, possibly after multiple requests with the
new API have been sent or at least queued up in the admin client?
When it's set to "requested", I think the suggestion was to just switch
over to the legacy API as soon as any request fails due to
targeting an incompatible broker. We could keep using the legacy API until
the mirrormaker setting is changed by the user or the mirrormaker restarts
instead of trying the new API every time it syncs the configurations. I'm
not sure which approach is the best here.
> 2) We don't replicate default properties from the source cluster right now
[2].
Won't making ConfigPropertyFilter::shouldReplicateSourceDefault return true
by default change that behavior? If so, what's the motivation for favoring
defaults from the source cluster over defaults for the target cluster,
especially given that users may already be relying on the opposite?
The concern was around what happens if deleting a topic config in
the source cluster. I initially thought, because the legacy API resets all
the configs other than the ones being altered, it effectively propagates
the deletions of a config in the source cluster. I thought by migrating to
incrementalAlterConfig API, the deletion would no longer get propagated but
looking into it again, it may not be the case.
If the user deletes a config in the source cluster, it would be reset to
the default value but the config source does not change back to
DEFAULT_CONFIG. For example:
./kafka-configs.sh --alter --entity-type topics --entity-name
quickstart-events --add-config retention.ms=720000 --bootstrap-server
localhost:9092
/kafka-configs.sh --describe --entity-type topics --entity-name
quickstart-events --bootstrap-server localhost:9092
Dynamic configs for topic quickstart-events are:
retention.ms=720000 sensitive=false synonyms={DYNAMIC_TOPIC_CONFIG:
retention.ms=720000}
./kafka-configs.sh --alter --entity-type topics --entity-name
quickstart-events --delete-config retention.ms --bootstrap-server
localhost:9092
/kafka-configs.sh --describe --entity-type topics --entity-name
quickstart-events --bootstrap-server localhost:9092
retention.ms=604800000 sensitive=false synonyms={}
Therefore, even with the legacy API, the deletion of the source topic does
not actually get propagated because isDefault() check here
<https://github.com/apache/kafka/blob/6e2b86597d9cd7c8b2019cffb895522deb63c93a/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorSourceConnector.java#L460>
would no longer return true. Basically, if a user deletes a config for the
source topic, with either API, the config on the target topic is
overwritten with the source cluster's default. if I understood this
correctly, maybe we don't need to extend ConfigPropertyFilter as it would
still rely on DEFAULT_CONFIG config source and the KIP is not changing the
current behaviour?
I have addressed the last comment from Chris about excluding code level
details from the proposed solution.
I also have addressed Luke's comment about the compatibility section.
Please let me know what you think.
Regards,
Tina
On Tue, Feb 7, 2023 at 8:06 AM Luke Chen <show...@gmail.com> wrote:
> Hi Tina,
>
> Thanks for the KIP to fix the issue.
>
> Some comments:
> 1. In the compatibility section, you said:
> `By default, the new setting will be set to false so it does not change the
> current behaviour.`
>
> I'm confused, what is the config we need to set to `false` to avoid
> breaking compatibility?
> All I can see is there is one new config introduced:
> use.incremental.alter.configs, and default to "requested".
> Does that mean it'll change current behavior?
> If so, I think we should make it clear in the compatibility section about
> what will be changed after this KIP.
>
> 2. It looks like you're going to introduce a new method in the existing
> interface. Could you follow the pattern in other KIP (ex: KIP-888
> <
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-888%3A+Batch+describe+ACLs+and+describe+client+quotas#KIP888:BatchdescribeACLsanddescribeclientquotas-NewAdminAPIs
> >)
> to list the javadoc and the method name together?
>
> Thank you.
> Luke
>
>
> On Fri, Feb 3, 2023 at 11:46 PM Chris Egerton <chr...@aiven.io.invalid>
> wrote:
>
> > Hi Tina,
> >
> > Thanks for the KIP! I recently ran into this exact issue and it's great
> to
> > see a fix being proposed. I have a few small comments but overall this
> > looks good:
> >
> > 1) The current logic for syncing topic configs in MM2 is basically
> > fire-and-forget; all we do is log a warning message [1] if an attempt
> > fails. When "use.incremental.alter.configs" is set to "requested", we'll
> > need to know whether attempts using the incremental API succeed or not,
> and
> > then adjust our behavior accordingly. Will the plan here be to block on
> the
> > success/failure of the first request before sending any more, or will we
> > just switch over to the legacy API as soon as any request fails due to
> > targeting an incompatible broker, possibly after multiple requests with
> the
> > new API have been sent or at least queued up in the admin client?
> >
> > 2) We don't replicate default properties from the source cluster right
> now
> > [2].
> > Won't making ConfigPropertyFilter::shouldReplicateSourceDefault return
> true
> > by default change that behavior? If so, what's the motivation for
> favoring
> > defaults from the source cluster over defaults for the target cluster,
> > especially given that users may already be relying on the opposite?
> >
> > 3) Nit: IMO the parts in the "proposed changes" section that detail
> changes
> > to internal classes aren't really necessary since they're not relevant to
> > user-facing behavior and the classes/methods described in them might
> change
> > between now and when the PR for the KIP gets opened/reviewed/merged. I
> > think the only points that need to be in the KIP are the ones beginning
> > with "Extend ConfigPropertyFilter class", "Add a new configuration
> setting
> > to MirrorMaker", and "From Kafka 4.0" (which itself can just describe the
> > broker APIs that are used by MM2 in general, without referring to the
> > specific name of the method in MM2 that will call them).
> >
> > [1] -
> >
> >
> https://github.com/apache/kafka/blob/6e2b86597d9cd7c8b2019cffb895522deb63c93a/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorSourceConnector.java#L429
> >
> > [2] -
> >
> >
> https://github.com/apache/kafka/blob/6e2b86597d9cd7c8b2019cffb895522deb63c93a/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorSourceConnector.java#L460
> >
> > Thanks again for the KIP!
> >
> > Cheers,
> >
> > Chris
> >
> > On Wed, Jan 25, 2023 at 10:44 AM Gantigmaa Selenge <gsele...@redhat.com>
> > wrote:
> >
> > > Hi,
> > >
> > > If there are no further comments on the KIP, I will start a vote on it.
> > >
> > > Regards,
> > >
> > >
> > > On Mon, Jan 16, 2023 at 11:14 AM Gantigmaa Selenge <
> gsele...@redhat.com>
> > > wrote:
> > >
> > > > Thanks everyone.
> > > >
> > > > I took the suggestions and updated the KIP accordingly. Please let me
> > > know
> > > > if there is anything else I could improve on.
> > > >
> > > > Regards,
> > > > Tina
> > > >
> > > > On Sun, Jan 15, 2023 at 10:24 PM Ismael Juma <ism...@juma.me.uk>
> > wrote:
> > > >
> > > >> Hi Tina,
> > > >>
> > > >> See below.
> > > >>
> > > >> On Wed, Jan 11, 2023 at 3:03 AM Gantigmaa Selenge <
> > gsele...@redhat.com>
> > > >> wrote:
> > > >>
> > > >> > I do like this idea, however when it's set to required, I wasn't
> > sure
> > > >> how
> > > >> > the mirrormaker should have. It's probably not a great experience
> if
> > > >> > mirrormaker starts crashing at some point after it's already
> running
> > > >> due to
> > > >> > an incompatible broker version.
> > > >> >
> > > >>
> > > >> This would only happen if the user explicitly requests the strict
> > > required
> > > >> ("non fallback") mode. There are many reasons why one may want this:
> > say
> > > >> you want to be sure that your system is not susceptible to the
> > > >> "alterConfigs" problems or you want to write a test that fails if
> > > >> "alterConfigs' is used.
> > > >>
> > > >>
> > > >> > If the incrementalAlterConfig request fails because the target
> > cluster
> > > >> is
> > > >> > running an older version, then we could log a WARN message that
> says
> > > >> > something like "The config to use incrementalAlterConfig API for
> > > >> syncing
> > > >> > topic configurations has been set to true however target cluster
> is
> > > >> running
> > > >> > incompatible version therefore using the legacy alterConfig API".
> > This
> > > >> way
> > > >> > the Mirrormaker never has to stop working and makes the user aware
> > of
> > > >> > what's being used.
> > > >>
> > > >>
> > > >> Logging statements are not great as the sole mechanism (although
> > useful
> > > as
> > > >> a complementary one) since one cannot easily test against them and
> > > they're
> > > >> often missed alongside all the other logging statements.
> > > >>
> > > >>
> > > >> > In this case, we also would not need 3 separate values
> > > >> > for the config, instead would use the original true or false
> values:
> > > >> > - true - > would use incrementalAlterConfig API, but if it's
> > > >> unavailable,
> > > >> > fallback to the legacy API
> > > >> > - false -> keep using the legacy API
> > > >> >
> > > >> > Set the flag to true by default and remove the config in 4.0.
> > > >> >
> > > >>
> > > >> But this means you have different behavior depending on the
> > > >> supported versions forever. Even though the config values are
> simpler,
> > > >> it's
> > > >> harder to reason about the behavior.
> > > >>
> > > >> > One suggestion: I'm not sure how concerned you are about people's
> > > >> ability
> > > >> > to migrate, but if you want to make it as smooth as possible, you
> > > could
> > > >> add
> > > >> > one more step. In the 4.0 release, while removing
> > > >> > `use.incremental.alter.configs`, you can also add
> > > >> > `use.legacy.alter.configs` to give users a path to continue using
> > the
> > > >> old
> > > >> > behavior even after the default changes.
> > > >> >
> > > >> > If we implement the fallback logic as Ismael suggested above, I
> > think
> > > we
> > > >> > would not need this extra flag later anymore.
> > > >> >
> > > >> > Please let me know what you think. Then I can go ahead and update
> > the
> > > >> KIP.
> > > >>
> > > >>
> > > >> IncrementalAlterConfigs has been around since Apache Kafka 2.3,
> > released
> > > >> in
> > > >> June 2019. By the time Apache Kafka 4.0 is released, it will have
> been
> > > at
> > > >> least 4.5 years. I think it's reasonable to set it as the new
> baseline
> > > and
> > > >> not maintain the fallback code. The key benefit is having behavior
> > that
> > > is
> > > >> easy to reason about.
> > > >>
> > > >> Ismael
> > > >>
> > > >
> > >
> >
>
