omkreddy commented on a change in pull request #11539:
URL: https://github.com/apache/kafka/pull/11539#discussion_r760946183



##########
File path: docs/upgrade.html
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@@ -19,6 +19,48 @@
 
 <script id="upgrade-template" type="text/x-handlebars-template">
 
+<h4><a id="upgrade_3_1_0" href="#upgrade_3_1_0">Upgrading to 3.1.0 from any 
version 0.8.x through 3.0.x</a></h4>
+
+<p><b>If you are upgrading from a version prior to 2.1.x, please see the note 
below about the change to the schema used to store consumer offsets.
+    Once you have changed the inter.broker.protocol.version to the latest 
version, it will not be possible to downgrade to a version prior to 2.1.</b></p>
+
+<p><b>For a rolling upgrade:</b></p>
+
+<ol>
+    <li>Update server.properties on all brokers and add the following 
properties. CURRENT_KAFKA_VERSION refers to the version you
+        are upgrading from. CURRENT_MESSAGE_FORMAT_VERSION refers to the 
message format version currently in use. If you have previously
+        overridden the message format version, you should keep its current 
value. Alternatively, if you are upgrading from a version prior
+        to 0.11.0.x, then CURRENT_MESSAGE_FORMAT_VERSION should be set to 
match CURRENT_KAFKA_VERSION.
+        <ul>
+            <li>inter.broker.protocol.version=CURRENT_KAFKA_VERSION (e.g., 
<code>3.0</code>, <code>2.8</code>, etc.)</li>
+            <li>log.message.format.version=CURRENT_MESSAGE_FORMAT_VERSION  
(See <a href="#upgrade_10_performance_impact">potential performance impact
+                following the upgrade</a> for the details on what this 
configuration does.)</li>
+        </ul>
+        If you are upgrading from version 0.11.0.x or above, and you have not 
overridden the message format, then you only need to override
+        the inter-broker protocol version.
+        <ul>
+            <li>inter.broker.protocol.version=CURRENT_KAFKA_VERSION (e.g., 
<code>3.0</code>, <code>2.8</code>, etc.)</li>
+        </ul>
+    </li>
+    <li>Upgrade the brokers one at a time: shut down the broker, update the 
code, and restart it. Once you have done so, the
+        brokers will be running the latest version and you can verify that the 
cluster's behavior and performance meets expectations.
+        It is still possible to downgrade at this point if there are any 
problems.
+    </li>
+    <li>Once the cluster's behavior and performance has been verified, bump 
the protocol version by editing
+        <code>inter.broker.protocol.version</code> and setting it to 
<code>3.1</code>.
+    </li>
+    <li>Restart the brokers one by one for the new protocol version to take 
effect. Once the brokers begin using the latest
+        protocol version, it will no longer be possible to downgrade the 
cluster to an older version.
+    </li>
+    <li>If you have overridden the message format version as instructed above, 
then you need to do one more rolling restart to
+        upgrade it to its latest version. Once all (or most) consumers have 
been upgraded to 0.11.0 or later,
+        change log.message.format.version to 2.8 on each broker and restart 
them one by one. Note that the older Scala clients,

Review comment:
       => change log.message.format.version to `3.1` 




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