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Re: Backwards compatibility for REST API


Thanks for bringing this issue up Thomas. I think you've raised a very
important point that we should try to provide not only for the programming
API but also for the REST API compatibility guarantees. Otherwise it is
really hard for 3rd party applications to integrate with Flink.

I think first as a very important step we should try to finalize the
versioning of the REST API as Chesnay suggested. Next we could add another
check list item to the PR template which specifically says that REST
changes need a thorough review. Ideally we could automate the compatibility
check but I'm not aware of a suitable tool for it. Has anyone experience
with any relevant tools?

Cheers,
Till

On Tue, Jul 24, 2018 at 5:53 PM Chesnay Schepler <chesnay@xxxxxxxxxx> wrote:

> Looked some more into it, as of _right now_ a 1.5.X client will not work
> against 1.6.0 cluster
> since the submission body was extended. But we could add a guard against
> this.
>
> On 24.07.2018 17:27, Chesnay Schepler wrote:
> > Note that the changes made to the REST API will in the long-term
> > reduce friction between versions,
> > as we no longer have to submit data through the blob service, which is
> > another internal API.
> >
> > On 24.07.2018 17:25, Chesnay Schepler wrote:
> >> /Will it be possible to submit a job graph built by 1.5.1 client
> >> (that does not contain any connectors or operators that depend on
> >> internal API) to 1.6.x job manager?/
> >>
> >> Probably yes, but generally there's no guarantee.
> >>
> >> The JobGraph is not a public API and thus may change in ways that could
> >> cause serialization failures if the client and server versions do not
> >> match.
> >>
> >> On 24.07.2018 17:12, Thomas Weise wrote:
> >>> I would expect more external dependencies on the REST API and
> >>> suggest to
> >>> consider versioning and compatibility guarantees.
> >>>
> >>> The particular issue is from Beam and tracked here:
> >>> https://issues.apache.org/jira/browse/BEAM-4842
> >>>
> >>> I would be surprised if that is the only instance besides Flink CLI
> >>> trying
> >>> to use the REST API for job submission. In the case of Beam, it is
> >>> problematic to assume that the job service that contains the Flink
> >>> client
> >>> will always be upgraded lock step with the server.
> >>>
> >>> What other factors prevent interoperability between Flink versions?
> >>> Will it
> >>> be possible to submit a job graph built by 1.5.1 client (that does not
> >>> contain any connectors or operators that depend on internal API) to
> >>> 1.6.x
> >>> job manager?
> >>>
> >>> Thanks,
> >>> Thomas
> >>>
> >>>
> >>> On Tue, Jul 24, 2018 at 7:58 AM Chesnay Schepler
> >>> <chesnay@xxxxxxxxxx> wrote:
> >>>
> >>>> Effectively there are no guarantees for backwards compatibility,
> >>>> although we try to maintain it.
> >>>>
> >>>> There are plans to version the REST API
> >>>> (https://issues.apache.org/jira/browse/FLINK-7551) but no definitive
> >>>> timeline.
> >>>>
> >>>> The change you mentioned in particular primarily affects internal code
> >>>> (since the removed endpoint is usually only used by the flink CLI).
> >>>> Note we do not provide any guarantee that Flink components interact
> >>>> properly if the versions don't exactly match, so you should always
> >>>> upgrade
> >>>> the clients anyway.
> >>>>
> >>>> On 24.07.2018 16:43, Thomas Weise wrote:
> >>>>> Hi,
> >>>>>
> >>>>> Are there any compatibility guarantees for the Flink REST API or
> >>>>> plans to
> >>>>> establish the same?
> >>>>>
> >>>>> I'm asking since I noticed that the 1.5.1 release has an incompatible
> >>>>> change that prevents a 1.5.0 client to submit a job to 1.5.0 server
> >>>>> (FLINK-9280, removed endpoint /blobserver/port).
> >>>>>
> >>>>> Such change is especially unexpected in a patch release, but even
> >>>>> if it
> >>>> was
> >>>>> in 1.6.x, it is still problematic because it forces clients to
> >>>>> upgrade.
> >>>>>
> >>>>> Thanks,
> >>>>> Thomas
> >>>>>
> >>>>
> >>
> >>
> >
> >
>
>