[jira] [Commented] (HADOOP-11656) Classpath isolation for downstream clients

["Christopher Tubbs (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-11656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15973268#comment-15973268 ] 

Christopher Tubbs commented on HADOOP-11656:
--------------------------------------------

As the current maintainer of Hadoop in the Fedora Linux distribution, I'm a bit concerned that the goal here is basically to statically compile everything from the dependencies (bugs, security issues, and all) into the Hadoop distribution jars. This would make downstream packaging in Fedora (and other distros which rely on packagers to do dependency convergence) much more difficult, as static compilation / bundling is essentially disallowed (some exceptions), because packages don't benefit from system updates of their dependencies, creating security risks and bad user experiences.

Am I misunderstanding what is being pursued here? Or is this basically bundling?

If this is bundling, I may be able to work around it by patching out the bundled deps for Fedora builds, but this is somewhat inconvenient, and I'd rather upstream Hadoop do things that make it easier on downstream community and vendor packaging. If I'm understanding the situation correctly, perhaps there's a better way to resolve dependency convergence issues? I've found that often, just following semantic versioning, and keeping dependencies reasonably up-to-date resolves most issues. (For example, one of the biggest issues I've had depending on Hadoop is its dependency on the old mortbay jetty, which is so full of security issues and so out of date, I'm surprised it's not a constant source of CVEs for Hadoop itself.)

Has the upstream Hadoop community considered other possible options, such as better semantic versioning, modularity, updated dependencies, marking dependencies "optional", relying on user-defined classpath at runtime, etc., as an alternative to shading/bundling? What is the basis for selecting shading as the solution instead of some of these other options?

Perhaps I'm completely misunderstanding the situation. If so, please explain where I've misunderstood.

Thanks.

> Classpath isolation for downstream clients
> ------------------------------------------
>
>                 Key: HADOOP-11656
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11656
>             Project: Hadoop Common
>          Issue Type: New Feature
>            Reporter: Sean Busbey
>            Assignee: Sean Busbey
>            Priority: Blocker
>              Labels: classloading, classpath, dependencies, scripts, shell
>         Attachments: HADOOP-11656_proposal.md
>
>
> Currently, Hadoop exposes downstream clients to a variety of third party libraries. As our code base grows and matures we increase the set of libraries we rely on. At the same time, as our user base grows we increase the likelihood that some downstream project will run into a conflict while attempting to use a different version of some library we depend on. This has already happened with i.e. Guava several times for HBase, Accumulo, and Spark (and I'm sure others).
> While YARN-286 and MAPREDUCE-1700 provided an initial effort, they default to off and they don't do anything to help dependency conflicts on the driver side or for folks talking to HDFS directly. This should serve as an umbrella for changes needed to do things thoroughly on the next major version.
> We should ensure that downstream clients
> 1) can depend on a client artifact for each of HDFS, YARN, and MapReduce that doesn't pull in any third party dependencies
> 2) only see our public API classes (or as close to this as feasible) when executing user provided code, whether client side in a launcher/driver or on the cluster in a container or within MR.
> This provides us with a double benefit: users get less grief when they want to run substantially ahead or behind the versions we need and the project is freer to change our own dependency versions because they'll no longer be in our compatibility promises.
> Project specific task jiras to follow after I get some justifying use cases written in the comments.



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