hachikuji commented on code in PR #12682:
URL: https://github.com/apache/kafka/pull/12682#discussion_r980495338
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docs/security.html:
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@@ -36,7 +36,104 @@ <h3 class="anchor-heading"><a id="security_overview"
class="anchor-link"></a><a
The guides below explain how to configure and use the security features in
both clients and brokers.
- <h3 class="anchor-heading"><a id="security_ssl" class="anchor-link"></a><a
href="#security_ssl">7.2 Encryption and Authentication using SSL</a></h3>
+ <h3 class="anchor-heading"><a id="listener_configuration"
class="anchor-link"></a><a href="#listener_configuration">7.2 Listener
Configuration</a></h3>
+
+ <p>In order to secure a Kafka cluster, it is necessary to secure the
channels that are used to
+ communicate with the servers. Each node must define the set of listeners
that are used to
+ receive requests from clients as well as other servers. Each listener
may be configured
+ to authenticate clients using various mechanisms and to ensure traffic
between the
+ server and the client is encrypted. This section provides a primer for
the configuration
+ of listeners.</p>
+
+ <p>Kafka brokers support listening for connections on multiple ports. This
is configured through
+ the <code>listeners</code> property in the server configuration, which
accepts a comma-separated
+ list of the listeners to enable. At least one listener must be defined
on each node. The format
+ of each listener defined in <code>listeners</code> is given below:</p>
+
+ <pre class="line-numbers"><code
class="language-text">{LISTENER_NAME}://{hostname}:{port}</code></pre>
+
+ <p>The <code>LISTENER_NAME</code> is usually a descriptive name which
defines the purpose of
+ the listener. For example, many configurations use a separate listener
for client traffic,
+ so they might refer to the corresponding listener as <code>CLIENT</code>
in the configuration:</p
+
+ <pre class="line-numbers"><code
class="language-text">listeners=CLIENT://localhost:9092</code></pre>
+
+ <p>The security protocol of each listener is defined in a separate
configuration:
+ <code>listener.security.protocol.map</code>. The value is a
comma-separated list
+ of each listener mapped to its security protocol. For example, the
follow value
+ configuration specifies that the <code>CLIENT</code> listener will use
SSL while the
+ <code>BROKER</code> listener will use plaintext.</p>
+
+ <pre class="line-numbers"><code
class="language-text">listener.security.protocol.map=CLIENT:SSL,BROKER:PLAINTEXT</code></pre>
+
+ <p>Possible options for the security protocol are given below:</p>
+ <ol>
+ <li>PLAINTEXT</li>
+ <li>SSL</li>
+ <li>SASL_PLAINTEXT</li>
+ <li>SASL_SSL</li>
+ </ol>
+
+ <p>The plaintext protocol provides no security and does not require any
additional configuration.
+ In the following sections, this document covers how to configure the
remaining protocols.</p>
+
+ <p>If each required listener uses a separate security protocol, it is also
possible to use the
+ security protocol name as the listener name in <code>listeners</code>.
Using the example above,
+ we could skip the definition of the <code>CLIENT</code> and
<code>BROKER</code> listeners
+ using the following definition:</p>
+
+ <pre class="line-numbers"><code
class="language-text">listeners=SSL://localhost:9092,PLAINTEXT://localhost:9093</code></pre>
+
+ <p>However, we recommend users to provide explicit names for the listeners
since it
+ makes the intended usage clearer.</p>
+
+ <p>Among the listeners in this list, it is possible to declare the
listener to be used for
+ inter-broker communication by setting the
<code>inter.broker.listener.name</code> configuration
+ to the name of the listener. If not defined, then the inter-broker
listener is determined
+ by the security protocol defined by
<code>security.inter.broker.protocol</code>, which
+ defaults to <code>PLAINTEXT</code>.</p>
+
+ <p>For legacy clusters which rely on Zookeeper to store cluster metadata,
it is possible to
+ declare a separate listener to be used for metadata propagation from the
active controller
+ to the brokers. This is defined by
<code>control.plane.listener.name</code>. The active controller
+ will use this listener when it needs to push metadata updates to the
brokers in the cluster.
+ The benefit of using a control plane listener is that it uses a separate
processing thread,
+ which makes it less likely for application traffic to impede timely
propagation of metadata changes
+ (such as partition leader and ISR updates). Note that the default value
is null, which
+ means that the controller will use the same listener as defined by
<code>inter.broker.listener</code></p>
+
+ <p>In a KRaft cluster, the listener defined by
<code>inter.broker.listener.name</code> is used
+ exclusively for requests sent to nodes which have the "broker" role
enabled in <code>process.roles</code>.
+ For legacy clusters, the active controller will connect to all brokers
in the cluster
+ to send metadata updates. In KRaft, it is the other way around. The
broker is responsible
+ for finding the current controller and connecting to it in order to
receive metadata updates.
+ Hence the configuration <code>control.plane.listener.name</code> cannot
be used in KRaft clusters.</p>
Review Comment:
Let me try to make the comment more concise. I just wanted a brief
explanation for why the control plane listener doesn't exist in KRaft clusters.
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