ijuma commented on code in PR #20334:
URL: https://github.com/apache/kafka/pull/20334#discussion_r2531498294
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docs/upgrade.html:
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@@ -113,6 +113,35 @@ <h5><a id="upgrade_420_notable"
href="#upgrade_420_notable">Notable changes in 4
<li>
The <code>num.replica.fetchers</code> config has a new lower bound of
1.
</li>
+ <li>
+ Improvements have been made to the validation rules and default values
of LIST-type configurations
+ (<a href="https://cwiki.apache.org/confluence/x/HArXF";>KIP-1161</a>).
+ <ul>
+ <li>
+ LIST-type configurations now enforce stricter validation:
+ <ul>
+ <li>Null values are no longer accepted for most LIST-type
configurations, except those that explicitly
+ allow a null default value or where a null value has a
well-defined semantic meaning.</li>
+ <li>Duplicate entries within the same list are no longer
permitted.</li>
Review Comment:
Typically yes.
For increased lower bound, there are two approaches that have good
compatibility characteristics:
1. Enforce the new lower bound at the API layer so existing cases that
seemingly have been working fine continue to work.
2. Automatically adjust the config to be at the new lower bound.
Whether to go with these versus something that requires user action depends
on the specifics. If it's truly unsafe to use a config value below the lower
bound and it's also unsafe to automatically adjust it, then you'd want to do
something stronger. But that is a high bar and often not met for configs that
have existed for a long time.
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