capistrant opened a new pull request, #17955: URL: https://github.com/apache/druid/pull/17955
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Don't reference the issue in the title of this pull-request. --> <!-- If you are a committer, follow the PR action item checklist for committers: https://github.com/apache/druid/blob/master/dev/committer-instructions.md#pr-and-issue-action-item-checklist-for-committers. --> ### Description <!-- Describe the goal of this PR, what problem are you fixing. If there is a corresponding issue (referenced above), it's not necessary to repeat the description here, however, you may choose to keep one summary sentence. --> <!-- Describe your patch: what did you change in code? How did you fix the problem? --> <!-- If there are several relatively logically separate changes in this PR, create a mini-section for each of them. For example: --> Modify the supervisor API to add restrictions on modifications to existing Kafka Supervisor Specs. Prevent the changing of the "stream" for an existing spec. This effectively means, that you cannot submit a spec update that makes a change to `topic`, a migration between `topic` and `topicPattern` or a change to a `topicPattern`. The reasoning for this is that the system is not designed to gracefully handle such migrations. In the best case, tasks will fail. And in the worst case, tasks will succeed but the metadata will not be being persisted correctly, leading to eventual data integrity issues. #### SupervisorSpec Interface Modification The core of the change lies here with a new interface method: `void validateProposedSpecEvolution(SupervisorSpec that) throws IllegalArgumentException;` This method is intended to determine if a proposed evolution of the existing spec to `that` proposed spec is allowed. The way it is spec'd out in this PR that an illegal proposed evolution results in the throwing of an `IllegalArgumentException`. The only implementation that actually has logic is KafkaSupervisorSpec which prevents the changing of the topic/topicPattern for the existing supervisor. All other spec evolution is allowed. <!-- In each section, please describe design decisions made, including: - Choice of algorithms - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such as when there are insufficient resources? - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns) - Method organization and design (how the logic is split between methods, parameters and return types) - Naming (class, method, API, configuration, HTTP endpoint, names of emitted metrics) --> <!-- It's good to describe an alternative design (or mention an alternative name) for every design (or naming) decision point and compare the alternatives with the designs that you've implemented (or the names you've chosen) to highlight the advantages of the chosen designs and names. --> ### Alternatives #### Support changes in topic/topicPattern An alternative approach to this would be modifying the system to properly handle change in the topic/topicPattern. I think that is still a good long term plan. But it would require defining exactly what evolution is allowed to occur. You could technically allow any kind of change in the topic/topicPattern, but it is debatable if you want to. For instance, allowing users unbounded ability to change the topic/topicPattern could lead to mistakes that behave how designed, but result in data issues for the user because they did something they didn't intend to, like remove a topic from their supervisor when they actually only meant to add a topic to the set of topics supplying data for the supervisor. #### Allow the spec change but prevent the start of tasks if the underlying topic set doesn't match metadata store Another approach I considered but did not pursue, so I don't know the true viability. would be to accept the spec submission, but not start up new tasks if the topic set in metadata didn't match what the new supervisor was actually seeing from Kafka. I think this would have allowed the change to stay confined to the kafka extension, with the tradeoff being that the feedback to the user wasn't as immediate as my implementation. #### Other thoughts Perhaps, an ideal world would be to identify a way to achieve this immediate negative feedback to the user, while still not modifying code outside of the kafka extension. I am open to hearing these ideas, so I labeled with design review. <!-- If there was a discussion of the design of the feature implemented in this PR elsewhere (e. g. a "Proposal" issue, any other issue, or a thread in the development mailing list), link to that discussion from this PR description and explain what have changed in your final design compared to your original proposal or the consensus version in the end of the discussion. If something hasn't changed since the original discussion, you can omit a detailed discussion of those aspects of the design here, perhaps apart from brief mentioning for the sake of readability of this PR description. --> <!-- Some of the aspects mentioned above may be omitted for simple and small changes. --> #### Release note <!-- Give your best effort to summarize your changes in a couple of sentences aimed toward Druid users. If your change doesn't have end user impact, you can skip this section. For tips about how to write a good release note, see [Release notes](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#release-notes). --> Explicitly prevent Kafka Supervisors from updating the underlying topic / topicPartition that is persisted for it. This behavior, while allowed by the API is not fully supported by the underlying system. A request to make such a change will result in a `400` error from the Supervisor API with details on the reason why it is not allowed. The docs and the message in the response describe a work-a-round for users who are adamant that they want to make such a change. <hr> ##### Key changed/added classes in this PR * `SupervisorSpec` * `KafkaSupervisorSpec` <hr> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. None of the items from the checklist below are strictly necessary, but it would be very helpful if you at least self-review the PR. --> This PR has: - [ ] been self-reviewed. - [ ] using the [concurrency checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md) (Remove this item if the PR doesn't have any relation to concurrency.) - [ ] added documentation for new or modified features or behaviors. - [ ] a release note entry in the PR description. - [X] 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) - [X] 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. - [X] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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