MINOR: Add upgrade guide for
Reviewers: A. Sophie Blee-Goldman
<h5><a id="upgrade_250_notable" href="#upgrade_250_notable">Notable changes in 2.5.0</a></h5>
<ul>
+ <li>When <code>RebalanceProtocol#COOPERATIVE</code> is used, <code>Consumer#poll</code> can still return data
+ while it is in the middle of a rebalance for those partitions still owned by the consumer; in addition
+ <code>Consumer#commitSync</code> now may throw a non-fatal <code>RebalanceInProgressException</code> to notify
+ users of such an event, in order to distinguish from the fatal <code>CommitFailedException</code> and allow
+ users to complete the ongoing rebalance and then reattempt committing offsets for those still-owned partitions.</li>
<li>For improved resiliency in typical network environments, the default value of
<code>zookeeper.session.timeout.ms</code> has been increased from 6s to 18s and
<code>replica.lag.time.max.ms</code> from 10s to 30s.</li>
- <li>New DSL operator <code>cogroup()</code> has been added for aggregating multiple streams together at once</li>
+ <li>New DSL operator <code>cogroup()</code> has been added for aggregating multiple streams together at once.</li>
<li>Scala 2.11 is no longer supported. See
<a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-531%3A+Drop+support+for+Scala+2.11+in+Kafka+2.5">KIP-531</a>
for details.</li>
