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From Ismaël Mejía <ieme...@gmail.com>
Subject Re: Artifact staging in cross-language pipelines
Date Wed, 12 Jun 2019 09:42:02 GMT
Can you please add this to the design documents webpage.
https://beam.apache.org/contribute/design-documents/

On Wed, May 8, 2019 at 7:29 PM Chamikara Jayalath <chamikara@google.com> wrote:
>
>
>
> On Tue, May 7, 2019 at 10:21 AM Maximilian Michels <mxm@apache.org> wrote:
>>
>> Here's the first draft:
>> https://docs.google.com/document/d/1XaiNekAY2sptuQRIXpjGAyaYdSc-wlJ-VKjl04c8N48/edit?usp=sharing
>>
>> It's rather high-level. We may want to add more details once we have
>> finalized the design. Feel free to make comments and edits.
>
>
> Thanks Max. Added some comments.
>
>>
>>
>> > All of this goes back to the idea that I think the listing of
>> > artifacts (or more general dependencies) should be a property of the
>> > environment themselves.
>>
>> +1 I came to the same conclusion while thinking about how to store
>> artifact information for deferred execution of the pipeline.
>>
>> -Max
>>
>> On 07.05.19 18:10, Robert Bradshaw wrote:
>> > Looking forward to your writeup, Max. In the meantime, some comments below.
>> >
>> >
>> > From: Lukasz Cwik <lcwik@google.com>
>> > Date: Thu, May 2, 2019 at 6:45 PM
>> > To: dev
>> >
>> >>
>> >>
>> >> On Thu, May 2, 2019 at 7:20 AM Robert Bradshaw <robertwb@google.com>
wrote:
>> >>>
>> >>> On Sat, Apr 27, 2019 at 1:14 AM Lukasz Cwik <lcwik@google.com>
wrote:
>> >>>>
>> >>>> We should stick with URN + payload + artifact metadata[1] where
the only mandatory one that all SDKs and expansion services understand is the "bytes" artifact
type. This allows us to add optional URNs for file://, http://, Maven, PyPi, ... in the future.
I would make the artifact staging service use the same URN + payload mechanism to get compatibility
of artifacts across the different services and also have the artifact staging service be able
to be queried for the list of artifact types it supports.
>> >>>
>> >>> +1
>> >>>
>> >>>> Finally, we would need to have environments enumerate the artifact
types that they support.
>> >>>
>> >>> Meaning at runtime, or as another field statically set in the proto?
>> >>
>> >>
>> >> I don't believe runners/SDKs should have to know what artifacts each environment
supports at runtime and instead have environments enumerate them explicitly in the proto.
I have been thinking about a more general "capabilities" block on environments which allow
them to enumerate URNs that the environment understands. This would include artifact type
URNs, PTransform URNs, coder URNs, ... I haven't proposed anything specific down this line
yet because I was wondering how environment resources (CPU, min memory, hardware like GPU,
AWS/GCP/Azure/... machine types) should/could tie into this.
>> >>
>> >>>
>> >>>> Having everyone have the same "artifact" representation would be
beneficial since:
>> >>>> a) Python environments could install dependencies from a requirements.txt
file (something that the Google Cloud Dataflow Python docker container allows for today)
>> >>>> b) It provides an extensible and versioned mechanism for SDKs, environments,
and artifact staging/retrieval services to support additional artifact types
>> >>>> c) Allow for expressing a canonical representation of an artifact
like a Maven package so a runner could merge environments that the runner deems compatible.
>> >>>>
>> >>>> The flow I could see is:
>> >>>> 1) (optional) query artifact staging service for supported artifact
types
>> >>>> 2) SDK request expansion service to expand transform passing in
a list of artifact types the SDK and artifact staging service support, the expansion service
returns a list of artifact types limited to those supported types + any supported by the environment
>> >>>
>> >>> The crux of the issue seems to be how the expansion service returns
>> >>> the artifacts themselves. Is this going with the approach that the
>> >>> caller of the expansion service must host an artifact staging service?
>> >>
>> >>
>> >> The caller would not need to host an artifact staging service (but would
become effectively a proxy service, see my comment below for more details) as I would have
expected this to be part of the expansion service response.
>> >>
>> >>>
>> >>> There is also the question here is how the returned artifacts get
>> >>> attached to the various environments, or whether they get implicitly
>> >>> applied to all returned stages (which need not have a consistent
>> >>> environment)?
>> >>
>> >>
>> >> I would suggest returning additional information that says what artifact
is for which environment. Applying all artifacts to all environments is likely to cause issues
since some environments may not understand certain artifact types or may get conflicting versions
of artifacts. I would see this happening since an expansion service that aggregates other
expansion services seems likely, for example:
>> >>                               /-> ExpansionSerivce(Python)
>> >> ExpansionService(Aggregator) --> ExpansionService(Java)
>> >>                               \-> ExpansionSerivce(Go)
>> >
>> > All of this goes back to the idea that I think the listing of
>> > artifacts (or more general dependencies) should be a property of the
>> > environment themselves.
>> >
>> >>>> 3) SDK converts any artifact types that the artifact staging service
or environment doesn't understand, e.g. pulls down Maven dependencies and converts them to
"bytes" artifacts
>> >>>
>> >>> Here I think we're conflating two things. The "type" of an artifact
is
>> >>> both (1) how to fetch the bytes and (2) how to interpret them (e.g.
is
>> >>> this a jar file, or a pip tarball, or just some data needed by a DoFn,
>> >>> or ...) Only (1) can be freely transmuted.
>> >>
>> >>
>> >> Your right. Thinking about this some more, general artifact conversion is
unlikely to be practical because how to interpret an artifact is environment dependent. For
example, a requirements.txt used to install pip packages for a Python docker container depends
on the filesystem layout of that specific docker container. One could simulate doing a pip
install on the same filesystem, see the diff and then of all the packages in requirements.txt
but this quickly becomes impractical.
>> >>
>> >>>
>> >>>> 4) SDK sends artifacts to artifact staging service
>> >>>> 5) Artifact staging service converts any artifacts to types that
the environment understands
>> >>>> 6) Environment is started and gets artifacts from the artifact retrieval
service.
>> >>>>
>> >>>> On Wed, Apr 24, 2019 at 4:44 AM Robert Bradshaw <robertwb@google.com>
wrote:
>> >>>>>
>> >>>>> On Wed, Apr 24, 2019 at 12:21 PM Maximilian Michels <mxm@apache.org>
wrote:
>> >>>>>>
>> >>>>>> Good idea to let the client expose an artifact staging service
that the
>> >>>>>> ExpansionService could use to stage artifacts. This solves
two problems:
>> >>>>>>
>> >>>>>> (1) The Expansion Service not being able to access the Job
Server
>> >>>>>> artifact staging service
>> >>>>>> (2) The client not having access to the dependencies returned
by the
>> >>>>>> Expansion Server
>> >>>>>>
>> >>>>>> The downside is that it adds an additional indirection.
The alternative
>> >>>>>> to let the client handle staging the artifacts returned
by the Expansion
>> >>>>>> Server is more transparent and easier to implement.
>> >>>>>
>> >>>>> The other downside is that it may not always be possible for
the
>> >>>>> expansion service to connect to the artifact staging service
(e.g.
>> >>>>> when constructing a pipeline locally against a remote expansion
>> >>>>> service).
>> >>>>
>> >>>> Just to make sure, your saying the expansion service would return
all the artifacts (bytes, urls, ...) as part of the response since the expansion service wouldn't
be able to connect to the SDK that is running locally either.
>> >>>
>> >>> Yes. Well, more I'm asking how the expansion service would return any
>> >>> artifacts.
>> >>>
>> >>> What we have is
>> >>>
>> >>> Runner <--- SDK ---> Expansion service.
>> >>>
>> >>> Where the unidirectional arrow means "instantiates a connection with"
>> >>> and the other direction (and missing arrows) may not be possible.
>> >>
>> >>
>> >> I believe the ExpansionService Expand request should become a unidirectional
stream back to the caller so that artifacts could be sent back to the SDK (effectively mirroring
the artifact staging service API). So the expansion response would stream back a bunch artifact
data messages and also the expansion response containing PTransform information.
>> >
>> > +1.
>> >
>> >>>>>> Ideally, the Expansion Service won't return any dependencies
because the
>> >>>>>> environment already contains the required dependencies.
We could make it
>> >>>>>> a requirement for the expansion to be performed inside an
environment.
>> >>>>>> Then we would already ensure during expansion time that
the runtime
>> >>>>>> dependencies are available.
>> >>>>>
>> >>>>> Yes, it's cleanest if the expansion service provides an environment
>> >>>>> without all the dependencies provided. Interesting idea to make
this a
>> >>>>> property of the expansion service itself.
>> >>>>
>> >>>> I had thought this too but an opaque docker container that was built
on top of a base Beam docker container would be very difficult for a runner to introspect
and check to see if its compatible to allow for fusion across PTransforms. I think artifacts
need to be communicated in their canonical representation.
>> >>>
>> >>> It's clean (from the specification point of view), but doesn't allow
>> >>> for good introspection/fusion (aside from one being a base of another,
>> >>> perhaps).
>> >>>
>> >>>>>>> In this case, the runner would (as
>> >>>>>>> requested by its configuration) be free to merge environments
it
>> >>>>>>> deemed compatible, including swapping out beam-java-X
for
>> >>>>>>> beam-java-embedded if it considers itself compatible
with the
>> >>>>>>> dependency list.
>> >>>>>>
>> >>>>>> Could you explain how that would work in practice?
>> >>>>>
>> >>>>> Say one has a pipeline with environments
>> >>>>>
>> >>>>> A: beam-java-sdk-2.12-docker
>> >>>>> B: beam-java-sdk-2.12-docker + dep1
>> >>>>> C: beam-java-sdk-2.12-docker + dep2
>> >>>>> D: beam-java-sdk-2.12-docker + dep3
>> >>>>>
>> >>>>> A runner could (conceivably) be intelligent enough to know that
dep1
>> >>>>> and dep2 are indeed compatible, and run A, B, and C in a single
>> >>>>> beam-java-sdk-2.12-docker + dep1 + dep2 environment (with the
>> >>>>> corresponding fusion and lower overhead benefits). If a certain
>> >>>>> pipeline option is set, it might further note that dep1 and
dep2 are
>> >>>>> compatible with its own workers, which are build against sdk-2.12,
and
>> >>>>> choose to run these in embedded + dep1 + dep2 environment.
>> >>>>
>> >>>> We have been talking about the expansion service and cross language
transforms a lot lately but I believe it will initially come at the cost of poor fusion of
transforms since "merging" environments that are compatible is a difficult problem since it
brings up many of the dependency management issues (e.g. diamond dependency issues).
>> >>>
>> >>> I agree. I think expansion services offering "kitchen-sink"
>> >>> containers, when possible, can go far here. If we could at least
>> >>> recognize when one environment/set of deps is a superset of another,
>> >>> that could be an easy case that would yield a lot of benefit as well.
>> >>
>> >>
>> >> +1

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