Thanks again Stephane. Your comments were pretty accurate.
A "future work" section was added to account for the suggested enhancements
that will follow the initial release of classloading isolation.
Specifically regarding versioning, you are right, the corresponding KIP
that will describe versioning will include the required extensions to the
configuration as well.
-Konstantine
On Wed, May 3, 2017 at 5:49 PM, Stephane Maarek <
steph...@simplemachines.com.au> wrote:
> Glad you find the feedback useful !
> Definitely all the ideas should be split in reasonable length KIPs. I just
> want to make sure the ideas are not lost. I won’t create the subsequent
> KIPs because I’m not good enough to implement the changes, but happy to
> keep on providing feedback alongside the way.
>
> Regarding the versioning comments: yes there’s a version of Connector, but
> how is that referenced in the config? I believe no config exposes a
> “version” field, which would tie a configuration to a connector version?
> Regarding shipping connect with a few connectors, that’s fine, but once a
> capability to pull from maven is here, I’d rather have a vanilla
> lightweight connect. Anyway, discussions for later.
>
>
>
> On 4/5/17, 4:17 am, "Konstantine Karantasis" <konstant...@confluent.io>
> wrote:
>
> Thank you Stephane,
>
> your comments bring interesting and useful subjects to the discussion.
> I'm
> adding my replies below Ewen's comments.
>
>
> On Tue, May 2, 2017 at 10:15 PM, Ewen Cheslack-Postava <
> e...@confluent.io>
> wrote:
>
> > On Tue, May 2, 2017 at 10:01 PM, Stephane Maarek <
> > steph...@simplemachines.com.au> wrote:
> >
> > Excellent feedback, Stephane!
> >
> > Thanks for the work, it’s definitely needed!
> > > I’d like to suggest to take it one step further.
> > >
> > > To me, I’d like to see Kafka Connect the same way we have Docker
> and
> > > Docker repositories.
> > >
> > > Here’s how I would envision the flow:
> > > - Kafka Connect workers are just workers. They come with no jars
> > whatsoever
> > > - The REST API allow you to add a config to the connect cluster
> > > - The workers, seeing the config, pull the jars from the available
> > > (maven?) repositories (public or private)
> > >
> >
> > I think supporting this mode is really valuable. It seems *really*
> > attractive if you have some easily accessible, scalable, centralized
> > storage for connectors (i.e. some central distributed FS).
> >
> > But having to jump through these hoops (which presumably include
> some extra
> > URLs to point to the connectors, some definition of what that URL
> points to
> > e.g. zip of jars? uberjar? something with a more complex spec?) just
> to do
> > a quickstart seems like quite a bit of overhead. I think we should
> consider
> > both a) incremental progress that opens up new options but doesn't
> prevent
> > us from the ideal end state and b) all local testing/dev/prod use
> cases
> > (which is also why I still like having the plain old CLASSPATH option
> > available).
> >
> > I think the proposal leaves open the scope for this -- it doesn't
> specify
> > connector-specific overrides, but that's obviously something that
> could be
> > added easily.
> >
> >
> Regarding 1) the workers carrying no modules, I believe we are pretty
> close
> to this situation today, at least in terms of connectors. Still, I feel
> that whether we bundle a few basic modules with the framework is
> orthogonal
> to class loading isolation. I agree with you that Connectors,
> Converters
> and Transformations should be external modules that are loaded by the
> framework. But having a few basic ones shipped with Connect simplifies
> on-boarding and quickstarts significantly.
>
> Regarding 2) and 3) these are very good to have, and definitely belong
> to
> the near term vision for Kafka Connect. Many interesting things to do
> here,
> from programmatically fetching connectors and their dependencies from
> maven
> repos (using something like Aether maybe), to deciding to support
> certain
> types of module bundling such as zip, uberjars etc. However dealing
> with
> the issue of extended discoverability at this point seems to broaden
> significantly the scope of this KIP. I think it's more practical (and
> probably faster) to proceed in phases. I estimate that after this KIP,
> subsequent KIPs will be intuitive and quite transparent.
>
>
>
> > > - Classpath isolation comes into play so that the pulled jar
> doesn’t
> > > interact with other connectors
> > > - Additionally, I believe the config should have a “tag” or
> “version”
> > > (like docker really), so that
> > > o you can run different versions of the same connector on your
> connect
> > > cluster
> > > o configurations are strongly linked to a connector (right now if I
> > update
> > > my connector jars, I may break my configuration)
> > >
> >
> > We have versions on Connectors. We don't have them on
> transformations or
> > converters, which was definitely an oversight -- we should figure
> out how
> > to get them in there.
> >
> > I think none of the proposals here rule out taking advantage of
> versioning
> > in the future -- would it be helpful to add a "Future Work" section
> that
> > gives an idea of how we'd extend this in the future to handle
> versions as
> > well?
> >
> >
> Dealing with versioning was left out of the scope of this KIP because
> Transformations and Converters currently are not versioned. I like the
> idea
> of adding a Future Work section. I'll add one to highlight the
> intention to
> support versioning.
>
>
> >
> > > I know this is a bit out of scope, but if major changes are coming
> to
> > > connect then these are my two cents.
> > >
> >
> > :) I think we can address most of these incrementally, but keep the
> scope
> > here a bit smaller and more manageable (and hopefully get it into
> > 0.11.0.0!). I just don't want perfect to be the enemy of good --
> getting
> > the first step in as long as it doesn't cause problems down the line
> seems
> > like a good step.
> >
> >
> > >
> > > Finally, maybe extend that construct to Transformers. The ability
> to
> > > externalise transformers as jars would democratize their usage IMO
> > >
> >
> > This should definitely happen! It's important for pretty much any
> pluggable
> > component, though I think Transformations will, on average, have the
> fewest
> > extra dependencies. Connectors have the most, followed by
> Converters, then
> > Transformations. But I think Konstantine has mentioned these in the
> KIP --
> > if it could be clearer in the proposed changes, perhaps you could
> suggest
> > where to add details?
> >
> > -Ewen
> >
>
>
> Thanks again for the comments, let me know if this plan sounds good.
>
> -Konstantine
>
>
>
> >
> >
> > >
> > > On 3/5/17, 4:24 am, "Ewen Cheslack-Postava" <e...@confluent.io>
> wrote:
> > >
> > > Thanks for the KIP.
> > >
> > > A few responses inline, followed by additional comments.
> > >
> > > On Mon, May 1, 2017 at 9:50 PM, Konstantine Karantasis <
> > > konstant...@confluent.io> wrote:
> > >
> > > > Gwen, Randall thank you for your very insightful
> observations. I'm
> > > glad you
> > > > find this first draft to be an adequate platform for
> discussion.
> > > >
> > > > I'll attempt replying to your comments in order.
> > > >
> > > > Gwen, I also debated exactly the same two options: a)
> interpreting
> > > absence
> > > > of module path as a user's intention to turn off isolation
> and b)
> > > > explicitly using an additional boolean property. A few
> reasons why
> > I
> > > went
> > > > with b) in this first draft are:
> > > > 1) As Randall mentions, to leave the option of using a
> default
> > value
> > > open.
> > > > If not immediately in the first version of isolation, maybe
> in the
> > > future.
> > > > 2) I didn't like the implicit character of the choice of
> > > interpreting an
> > > > empty string as a clear intention to turn isolation off by
> the
> > user.
> > > Half
> > > > the time could be just that users forget to set a location,
> > although
> > > they'd
> > > > like to use class loading isolation.
> > > > 3) There's a slim possibility that in rare occasions a user
> might
> > > want to
> > > > avoid even the slightest increase in memory consumption due
> to
> > class
> > > > loading duplication. I admit this should be very rare, but
> given
> > the
> > > other
> > > > concerns and that we would really like to keep the isolation
> > > implementation
> > > > simple, the option to turn off this feature by using only one
> > > additional
> > > > config property might not seem too excessive. At least at
> the start
> > > of this
> > > > discussion.
> > > > 4) Debugging during development might be simpler in some
> cases.
> > > > 5) Finally, as you mention, this could allow for smoother
> upgrades.
> > > >
> > >
> > > I'm not sure any of these keep you from removing the extra
> config. Is
> > > there
> > > any reason you couldn't have clean support for relying on the
> > CLASSPATH
> > > while still supporting the classloaders? Then getting people
> onto the
> > > new
> > > classloaders does require documentation for how to install
> > connectors,
> > > but
> > > that's pretty minimal. And we don't break existing
> installations
> > where
> > > people are just adding to the CLASSPATH. It seems like this:
> > >
> > > 1. Allows you to set a default. Isolation is always enabled,
> but we
> > > won't
> > > include any paths/directories we already use. Setting a
> default just
> > > requires specifying a new location where we'd hold these
> directories.
> > > 2. It doesn't require the implicit choice -- you actually
> never turn
> > > off
> > > isolation, but still support the regular CLASSPATH with an
> empty list
> > > of
> > > isolated loaders
> > > 3. The user can still use CLASSPATH if they want to minimize
> > > classloader
> > > overhead
> > > 4. Debugging can still use CLASSPATH
> > > 5. Upgrades just work.
> > >
> > >
> > > >
> > > > Randall, regarding your comments:
> > > > 1) To keep its focus narrow, this KIP, as well as the first
> > > implementation
> > > > of isolation in Connect, assume filesystem based discovery.
> With
> > > careful
> > > > implementation, transitioning to discovery schemes that
> support
> > > broader
> > > > URIs I believe should be easy in the future.
> > > >
> > >
> > > Maybe just mention a couple of quick examples in the KIP. When
> > > described
> > > inline it might be more obvious that it will extend cleanly.
> > >
> > >
> > > > 2) The example you give makes a good point. However I'm
> inclined to
> > > say
> > > > that such cases should be addressed more as exceptions
> rather than
> > > as being
> > > > the common case. Therefore, I wouldn't see all dependencies
> > imported
> > > by the
> > > > framework as required to be filtered out, because in that
> case we
> > > lose the
> > > > advantage of isolation between the framework and the
> connectors
> > (and
> > > we are
> > > > left only with isolation between connectors).
> > >
> > > 3) I tried to abstract implementation details in this the KIP,
> but
> > you
> > > are
> > > > right. Even though filtering here is mainly used semantically
> > rather
> > > than
> > > > literally, it gives an implementation hint that we could
> avoid.
> > > >
> > >
> > > I think we're missing another option -- don't do filtering and
> > require
> > > that
> > > those dependencies are correctly filtered out of the modules.
> If we
> > > want to
> > > be nicer about this, we could also detect maybe 2 or 3 classes
> while
> > > scanning for Connectors/Converters/Transformations that
> indicate the
> > > classloader has jars that it shouldn't and warn about it. I
> can't
> > > think of
> > > that many that would be an issue -- basically connect-api,
> > > connect-runtime
> > > if they really mess it up, and maybe slf4j.
> > >
> > >
> > > > 4) In the same spirit as in 3) I believe we should reserve
> enough
> > > > flexibility to the implementation to discover and load
> classes,
> > when
> > > they
> > > > appear in multiple locations under the general module
> location.
> > > >
> > > >
> > > And a couple of addition comments:
> > >
> > > - module.path should be module.paths if it accepts multiple
> paths
> > > - I think the description of the module paths is a bit
> confusing
> > > because I
> > > think for simpler configuration we actually want to specify the
> > > *parent*
> > > directory of module paths. I definitely prefer this since it's
> > simpler
> > > although I am not certain how it will mix with future
> extensions to
> > > other
> > > URL handlers (where a zip file or http URL wouldn't do the same
> > > discovery
> > > within subdirectories)
> > >
> > > -Ewen
> > >
> > >
> > > > Thanks again! Let me know what you think.
> > > > Konstantine
> > > >
> > > >
> > > > On Mon, May 1, 2017 at 10:12 AM, Randall Hauch <
> rha...@gmail.com>
> > > wrote:
> > > >
> > > > > Very nice work, Konstantine. Conflicting dependencies of
> > > connectors is
> > > > > indeed a big issue that makes it hard to manage installed
> > > connectors.
> > > > >
> > > > > I do like Gwen's idea about removing the
> > 'module.isolation.enabled'
> > > > > property. However, I would have anticipated always using
> > classpath
> > > > > isolation for *only* those components registered under the
> module
> > > path
> > > > and
> > > > > not really for anything else already on the normal
> classpath. So,
> > > people
> > > > > could continue to place custom connector JARs onto the
> classpath,
> > > though
> > > > > this would become deprecated in favor of installing custom
> > > connector
> > > > JARs /
> > > > > modules via the module path. This keeps configuration
> simple,
> > gives
> > > > people
> > > > > time to migrate, but let's people that need classpath
> isolation
> > > get it to
> > > > > install a variety of connectors each with their
> dependencies that
> > > > > potentially conflict with other components.
> > > > >
> > > > > The challenge is whether there should be a default for
> > > 'module.path'.
> > > > > Ideally there would be so that users know where they can
> install
> > > their
> > > > > connectors. However, I suspect that this might be
> difficult to do
> > > unless
> > > > it
> > > > > can make use of system properties such as "${kafka.home}"
> so that
> > > > relative
> > > > > directories can be specified.
> > > > >
> > > > > A few other questions/comments:
> > > > >
> > > > > 1) Does the KIP have to specify how are components /
> modules
> > > installed,
> > > > > discovered, or recognized by Kafka Connect? Or perhaps the
> KIP
> > > needs to
> > > > > just specify the semantics of the file system module path
> (e.g.,
> > > the
> > > > > directories below those specified in the module path are
> to be
> > > unique and
> > > > > identify an installed component).
> > > > >
> > > > > 2) Will the module classloader filtering also have to
> exclude
> > Kafka
> > > > Connect
> > > > > dependencies? The only one that I can think of is the
> SLF4J API,
> > > which
> > > > > can't be loaded from the module's classloader if the
> connector is
> > > to send
> > > > > its log messages to the same logging system.
> > > > >
> > > > > 3) Rather than specify filtering, would be it a bit more
> flexible
> > > to
> > > > simply
> > > > > say that the implementation will need to ensure that Java,
> Kafka
> > > Connect,
> > > > > and other third party APIs (e.g., SLF4J API) will not be
> loaded
> > > from the
> > > > > module classloaders? It'd be better to avoid specifying
> how it
> > > will be
> > > > > done, just in case the implementation needs to evolve or
> use a
> > > different
> > > > > technique (e.g., load the Java and public Kafka Connect
> APIs via
> > > one
> > > > > classloader that is reused and that always appears before
> the
> > > module
> > > > > classloader, while Kafka Connect implementation JARs
> appear after
> > > the
> > > > > component's classloader.
> > > > >
> > > > > 4) Perhaps to address #2 and #3 above, perhaps the KIP
> could
> > > explicitly
> > > > > specify the classloader order for a deployed connector. For
> > > example,
> > > > > 'java', 'kafka-connect-apis', 'connector-module',
> 'smt-module-1',
> > > ...,
> > > > > 'kafka-connect-impls', where 'connector-module' is the
> > classloader
> > > for
> > > > the
> > > > > (first) module where the connector is found,
> 'smt-module-1' is
> > the
> > > > > classloader for the (first) module where the first SMT
> class is
> > > found (if
> > > > > specified and found in a separate module), 'smt-module-2'
> is the
> > > > > classloader .... Might also need to say that the KIP does
> not
> > > specify how
> > > > > the implementation will pick the module if a specified
> class if
> > > found in
> > > > > more than one module.
> > > > >
> > > > > Thoughts?
> > > > >
> > > > > Randall
> > > > >
> > > > > On Mon, May 1, 2017 at 6:43 AM, Gwen Shapira <
> g...@confluent.io>
> > > wrote:
> > > > >
> > > > > > Hi Konstantine,
> > > > > >
> > > > > > Thank you so much for driving this! The connector
> classpath
> > mess
> > > is
> > > > > driving
> > > > > > me nuts (or worse, driving me to use Docker).
> > > > > >
> > > > > > I like the proposal for micro-benchmarks to test the
> context
> > > switching
> > > > > > overhead.
> > > > > >
> > > > > > I have a difficult time figuring out the
> > > module.isolation.enabled.
> > > > > > Especially with a default to false. I can't think of a
> reason
> > > that
> > > > anyone
> > > > > > will not want classpath isolation. "No! I want my
> connectors to
> > > mess up
> > > > > > each other's dependencies" said no one ever.
> > > > > >
> > > > > > So it looks like this is mostly for upgrade purpose?
> Because
> > the
> > > > initial
> > > > > > upgrade will not have the module.path set and therefore
> > classpath
> > > > > isolation
> > > > > > will simply not work by default?
> > > > > >
> > > > > > In that case, why don't we simply use the existence of
> > non-empty
> > > > > > module.path as an indicator of whether isolation should
> work or
> > > not?
> > > > seem
> > > > > > simpler and intuitive to me.
> > > > > >
> > > > > > Thanks!
> > > > > >
> > > > > > Gwen
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > On Sat, Apr 29, 2017 at 9:16 AM, Konstantine Karantasis <
> > > > > > konstant...@confluent.io> wrote:
> > > > > >
> > > > > > > * Because of KIP number collision, please disregard my
> > > previous KIP
> > > > > > > announcement and use this thread for discussion
> instead *
> > > > > > >
> > > > > > >
> > > > > > > Hi everyone,
> > > > > > >
> > > > > > > we aim to address dependency conflicts in Kafka
> Connect soon
> > by
> > > > > applying
> > > > > > > class loading isolation.
> > > > > > >
> > > > > > > Feel free to take a look at KIP-146 here:
> > > > > > >
> > > > > > > *https://cwiki.apache.org/
> confluence/display/KAFKA/KIP-
> > > > > > > 146+-+Classloading+Isolation+in+Connect
> > > > > > > <https://cwiki.apache.org/
> confluence/display/KAFKA/KIP-
> > > > > > > 146+-+Classloading+Isolation+in+Connect>*
> > > > > > >
> > > > > > > which describes minimal required changes to public
> interfaces
> > > and the
> > > > > > > general implementation approach.
> > > > > > >
> > > > > > > This is a much wanted feature for Kafka Connect. Your
> > feedback
> > > is
> > > > > highly
> > > > > > > appreciated.
> > > > > > >
> > > > > > > -Konstantine
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > *Gwen Shapira*
> > > > > > Product Manager | Confluent
> > > > > > 650.450.2760 | @gwenshap
> > > > > > Follow us: Twitter <https://twitter.com/ConfluentInc> |
> blog
> > > > > > <http://www.confluent.io/blog>
> > > > > >
> > > > >
> > > >
> > >
> > >
> > >
> > >
> >
>
>
>
>
