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From Karthik Shashank Kambatla <ka...@cloudera.com>
Subject Re: [DISCUSS] merging YARN-2915 (Federation) to trunk
Date Fri, 23 Jun 2017 01:21:00 GMT
Given RTC and the amount of production testing this feature has received, I
am totally in favor of this merge.

On Tue, Jun 20, 2017 at 4:28 PM, Subru Krishnan <subru@apache.org> wrote:

> Hi all,
> We would like to open a discussion on merging the YARN Federation
> (YARN-2915) [1] feature to trunk.  We have been developing the feature in a
> feature branch (YARN-2915 [2]) for a while, and we are reasonably confident
> that the state of the feature meets the criteria to be merged onto trunk.
> *Key Ideas*:
> YARN’s centralized design allows strict enforcement of scheduling
> invariants and effective resource sharing, but becomes a scalability
> bottleneck (in number of jobs and nodes) well before reaching the scale of
> our clusters (e.g., 20k-50k nodes).
> To address these limitations, we developed a scale-out, federation-based
> solution (YARN-2915). Our architecture scales near-linearly to datacenter
> sized clusters, by partitioning nodes across multiple sub-clusters (each
> running a YARN cluster of few thousands nodes). Applications can span
> multiple sub-clusters *transparently (i.e. no code change or recompilation
> of existing apps)*, thanks to a layer of indirection that negotiates with
> multiple sub-clusters' Resource Managers on behalf of the application.
> This design is structurally scalable, as it bounds the number of nodes each
> RM is responsible for. Appropriate policies ensure that the majority of
> applications reside within a single sub-cluster, thus further controlling
> the load on each RM. This provides near linear scale-out by simply adding
> more sub-clusters. The same mechanism enables pooling of resources from
> clusters owned and operated by different teams.
> Status:
>    - The version we would like to merge to trunk is termed "MVP" (minimal
>    viable product). The feature will have a complete end-to-end application
>    execution flow with the ability to span a single application across
>    multiple YARN (sub) clusters.
>    - There were 50+ sub-tasks that were that were completed as part of this
>    effort. Every patch has been reviewed and +1ed by a committer. Thanks to
>    Jian, Wangda, Karthik, Vinod, Varun & Arun for the thorough reviews!
>    - Federation is designed to be built around YARN and consequently has
>    minimal code changes to core YARN. The relevant JIRAs that modify
> existing
>    YARN code base are YARN-3671 [7] & YARN-3673 [8]. We also paid close
>    attention to ensure that if federation is disabled there is zero impact
> to
>    existing functionality (disabled by default).
>    - We found a few bugs as we went along which we fixed directly upstream
>    in trunk and/or branch-2.
>    - We have continuously rebasing the feature branch [2] so the merge
>    should be a straightforward cherry-pick.
>    - The current version has been rather thoroughly tested and is currently
>    deployed in a *10,000+ node federated YARN cluster that's running
>    upwards of 50k jobs daily with a reliability of 99.9%*.
>    - We have few ideas for follow-up extensions/improvements which are
>    tracked in the umbrella JIRA YARN-5597[3].
> Documentation:
>    - Quick start guide (maven site) - YARN-6484[4].
>    - Overall design doc[5] and the slide-deck [6] we used for our talk at
>    Hadoop Summit 2016 is available in the umbrella jira - YARN-2915.
> Credits:
> This is a group effort that could have not been possible without the ideas
> and hard work of many other folks and we would like to specifically call
> out Giovanni, Botong & Ellen for their invaluable contributions. Also big
> thanks to the many folks in community  (Sriram, Kishore, Sarvesh, Jian,
> Wangda, Karthik, Vinod, Varun, Inigo, Vrushali, Sangjin, Joep, Rohith and
> many more) that helped us shape our ideas and code with very insightful
> feedback and comments.
> We plan to start the merge vote in the next week or so. The branch is close
> to complete (~5 patches before one can kick the tires on a running
> deployment). Please look through the branch; feedback is welcome. Thanks!
> Cheers,
> Subru & Carlo
> [1] YARN-2915: https://issues.apache.org/jira/browse/YARN-2915
> [2] https://github.com/apache/hadoop/tree/YARN-2915
> [3] YARN-5597: https://issues.apache.org/jira/browse/YARN-5597
> [4] YARN-6484: https://issues.apache.org/jira/browse/YARN-6484
> [5] https://issues.apache.org/jira/secure/attachment/12733292/
> Yarn_federation_design_v1.pdf
> [6] https://issues.apache.org/jira/secure/attachment/1281922
> 9/YARN-Federation-Hadoop-Summit_final.pptx
> [7] YARN-3671: https://issues.apache.org/jira/browse/YARN-3671
> [8] YARN-3673: https://issues.apache.org/jira/browse/YARN-3673

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