capistrant opened a new pull request, #20508:
URL: https://github.com/apache/druid/pull/20508
### Description
Instead of coupling the Dart worker to the Historical service, I think it
makes sense to tie an announced DartWorkerService component to historicals who
enable Dart engine via runtime property. If nothing else it adds some more rich
information to the historicals announced capabilities. But it also could
provide us future optionality in how Dart workers are registered and used. The
recommended guidance in dart docs continues to recommend setting the dart flag
in common runtime properties; so early adopters who already do that will see
zero impact or behavior change as long as they follow the rolling update order
of historicals before brokers in the Druid 39 upgrade.
Mostly things will stay exactly the same, but now the Dart controller will
only enroll actual Dart workers instead of all historicals without first
checking if they run Dart in the first place. This would avoid the controller
from sending Dart queries to a historical who explicitly disabled Dart.
#### Release note
Dart workers on historicals are announced and discovered by the broker with
a new DartWorkerService mechanism. Operators whose clusters have enabled dart
should be sure to follow the standard rolling upgrade/downgrade order where
historicals restart before broker during upgrade and the reverse during
downgrade.
<hr>
##### Key changed/added classes in this PR
* `DartControllerContext`
* `DartMessageRelays`
* `DartWorkerService`
<hr>
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This PR has:
- [ ] been self-reviewed.
- [ ] added documentation for new or modified features or behaviors.
- [ ] a release note entry in the PR description.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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