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https://issues.apache.org/jira/browse/KAFKA-13146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17389899#comment-17389899
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Tom Bentley commented on KAFKA-13146:
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{quote}We have also considered whether the internal __cluster_metadata topic
should be readable through the controller endpoints by consumers.{quote}
That's what I had expected when originally reading the various KIPs, but
exposing the metadata log comes with some downsides. Would consumers be able to
do {{read_committed}} reads?
> Consider client use cases for accessing controller endpoints
> ------------------------------------------------------------
>
> Key: KAFKA-13146
> URL: https://issues.apache.org/jira/browse/KAFKA-13146
> Project: Kafka
> Issue Type: Improvement
> Reporter: Jason Gustafson
> Priority: Major
> Labels: kip-500
>
> In KAFKA-13143, we dropped the Metadata from the controller APIs. We did this
> for two reasons. First, the implementation did not return any topic metadata.
> This was confusing for users who mistakenly tried to use the controller
> endpoint in order to describe or list topics since it would appear that no
> topics existed in the cluster. The second reason is that the implementation
> returned the controller endpoints. So even if we returned the topic metadata,
> clients would be unable to access the topics for reading or writing through
> the controller endpoint.
> So for 3.0, we are effectively saying that clients should only access the
> broker endpoints. Long term, is that what we want? When running the
> controllers as separate nodes, it may be useful to initialize the controllers
> and cluster metadata before starting any of the brokers, for example. For
> this to work, we need to put some thought into how the Metadata API should
> work with controllers. For example, we can return a flag or some kind of
> error code in the response to indicate that topic metadata is not available.
> We have also considered whether the internal __cluster_metadata topic should
> be readable through the controller endpoints by consumers.
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