cmccabe commented on code in PR #12642:
URL: https://github.com/apache/kafka/pull/12642#discussion_r971204480
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docs/ops.html:
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@@ -3180,6 +3180,119 @@ <h4 class="anchor-heading"><a id="zkops"
class="anchor-link"></a><a href="#zkops
<li>Don't overbuild the cluster: large clusters, especially in a write
heavy usage pattern, means a lot of intracluster communication (quorums on the
writes and subsequent cluster member updates), but don't underbuild it (and
risk swamping the cluster). Having more servers adds to your read capacity.</li>
</ul>
Overall, we try to keep the ZooKeeper system as small as will handle the
load (plus standard growth capacity planning) and as simple as possible. We try
not to do anything fancy with the configuration or application layout as
compared to the official release as well as keep it as self contained as
possible. For these reasons, we tend to skip the OS packaged versions, since it
has a tendency to try to put things in the OS standard hierarchy, which can be
'messy', for want of a better way to word it.
+
+ <h3 class="anchor-heading"><a id="kraft" class="anchor-link"></a><a
href="#kraft">6.10 KRaft</a></h3>
+
+ <h4 class="anchor-heading"><a id="kraft_config" class="anchor-link"></a><a
href="#kraft_config">Configuration</a></h4>
+
+ <h5 class="anchor-heading"><a id="kraft_role" class="anchor-link"></a><a
href="#kraft_role">Process Roles</a></h5>
+
+ <p>In KRaft mode each Kafka server can be configured as a controller, as a
broker or as both using the <code>process.roles<code> property. This property
can have the following values:</p>
+
+ <ul>
+ <li>If <code>process.roles</code> is set to <code>broker</code>, the
server acts as a broker.</li>
+ <li>If <code>process.roles</code> is set to <code>controller</code>, the
server acts as a controller.</li>
+ <li>If <code>process.roles</code> is set to
<code>broker,controller</code>, the server acts as a broker and a
controller.</li>
+ <li>If <code>process.roles</code> is not set at all, it is assumed to be
in ZooKeeper mode.</li>
+ </ul>
+
+ <p>Nodes that act as both brokers and controllers are referred to as
"combined" nodes. Combined nodes are simpler to operate for simple use cases
like a development environment. The key disadvantage is that the controller
will be less isolated from the rest of the system. Combined mode is not
recommended is critical deployment environments.</p>
+
+
+ <h5 class="anchor-heading"><a id="kraft_voter" class="anchor-link"></a><a
href="#kraft_voter">Controllers</a></h5>
+
+ <p>In KRaft mode, only a small group of specially selected servers can act
as controllers (unlike the ZooKeeper-based mode, where any server can become
the Controller). The specially selected controller servers will participate in
the metadata quorum. Each controller server is either active, or a hot standby
for the current active controller server.</p>
+
+ <p>A Kafka cluster will typically select 3 or 5 servers for this role,
depending on factors like cost and the number of concurrent failures your
system should withstand without availability impact. A majority of the
controllers must be alive in order to maintain availability. With 3
controllers, the cluster can tolerate 1 controller failure; with 5 controllers,
the cluster can tolerate 2 controller failures.</p>
+
+ <p>All of the servers in a Kafka cluster discover the quorum voters using
the <code>controller.quorum.voters</code> property. This identifies the quorum
controller servers that should be used. All the controllers must be enumerated.
Each controller is identified with their <code>id</code>, <code>host</code> and
<code>port</code> information. This is an example configuration:
<code>controller.quorum.voters=id1@host1:port1,id2@host2:port2,id3@host3:port3</code></p>
Review Comment:
can we put the example configuration in a PRE or CODE block, or whatever, so
it shows as monospace? (Just a thought)
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