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https://issues.apache.org/jira/browse/KAFKA-5693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16111313#comment-16111313
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Tom Bentley commented on KAFKA-5693:
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One (obvious) part solution to this is that the {{CreateTopicPolicy}} should be
applied not just at topic creation, but also for every topic modification,
whether it's a change to the topic configs or something else. Unless there's a
valid use case for configuring changed topics differently to freshly created
topics?
By symmetry, unless it's OK for a noop topic config change to be rejected by
the {{AlterConfigPolicy}}, maybe the topic config supplied during topic
creation should also be run through the {{AlterConfigPolicy}}. Again, maybe
there are valid use cases for allowing a topic config at creation which would
be disallowed in a later modification, but I can't think of any.
> TopicCreationPolicy and AlterConfigsPolicy overlap
> --------------------------------------------------
>
> Key: KAFKA-5693
> URL: https://issues.apache.org/jira/browse/KAFKA-5693
> Project: Kafka
> Issue Type: Bug
> Reporter: Tom Bentley
> Priority: Minor
>
> The administrator of a cluster can configure a {{CreateTopicPolicy}}, which
> has access to the topic configs as well as other metadata to make its
> decision about whether a topic creation is allowed. Thus in theory the
> decision could be based on a combination of of the replication factor, and
> the topic configs, for example.
> Separately there is an AlterConfigPolicy, which only has access to the
> configs (and can apply to configurable entities other than just topics).
> There are potential issues with this. For example although the
> CreateTopicPolicy is checked at creation time, it's not checked for any later
> alterations to the topic config. So policies which depend on both the topic
> configs and other topic metadata could be worked around by changing the
> configs after creation.
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