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<title>39.&nbsp;Apache Kafka Binder</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="multi_spring-cloud.html" title="Spring Cloud"><link rel="up" href="multi__binder_implementations.html" title="Part&nbsp;VI.&nbsp;Binder Implementations"><link rel="prev" href="multi__binder_implementations.html" title="Part&nbsp;VI.&nbsp;Binder Implementations"><link rel="next" href="multi__apache_kafka_streams_binder.html" title="40.&nbsp;Apache Kafka Streams Binder"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">39.&nbsp;Apache Kafka Binder</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__binder_implementations.html">Prev</a>&nbsp;</td><th width="60%" align="center">Part&nbsp;VI.&nbsp;Binder Implementations</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="multi__apache_kafka_streams_binder.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_apache_kafka_binder" href="#_apache_kafka_binder"></a>39.&nbsp;Apache Kafka Binder</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_usage" href="#_usage"></a>39.1&nbsp;Usage</h2></div></div></div><p>To use Apache Kafka binder all you need is to add <code class="literal">spring-cloud-stream-binder-kafka</code> as a dependency to your Spring Cloud Stream application. Below is a Maven example:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-stream-binder-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><p>Alternatively, you can also use the Spring Cloud Stream Kafka Starter.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-starter-stream-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_apache_kafka_binder_overview" href="#_apache_kafka_binder_overview"></a>39.2&nbsp;Apache Kafka Binder Overview</h2></div></div></div><p>A simplified diagram of how the Apache Kafka binder operates can be seen below.</p><div class="figure"><a name="d0e10841" href="#d0e10841"></a><p class="title"><b>Figure&nbsp;39.1.&nbsp;Kafka Binder</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/kafka-binder.png" alt="kafka binder"></div></div></div><br class="figure-break"><p>The Apache Kafka Binder implementation maps each destination to an Apache Kafka topic.
The consumer group maps directly to the same Apache Kafka concept.
Partitioning also maps directly to Apache Kafka partitions as well.</p><p>The binder currently uses the Apache Kafka <code class="literal">kafka-clients</code> 1.0.0 jar and is designed to be used with a broker at least that version.
This client can communicate with older brokers (refer to the Kafka documentation), but certain features may not be available.
For example, with versions earlier than 0.11.x.x, native headers are not supported.
Also, 0.11.x.x does not support the <code class="literal">autoAddPartitions</code> property.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_configuration_options_2" href="#_configuration_options_2"></a>39.3&nbsp;Configuration Options</h2></div></div></div><p>This section contains the configuration options used by the Apache Kafka binder.</p><p>For common configuration options and properties pertaining to binder, refer to the <a class="link" href="multi__configuration_options.html#binding-properties" title="31.2&nbsp;Binding Properties">core documentation</a>.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_kafka_binder_properties" href="#_kafka_binder_properties"></a>39.3.1&nbsp;Kafka Binder Properties</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">spring.cloud.stream.kafka.binder.brokers</span></dt><dd><p class="simpara">A list of brokers to which the Kafka binder will connect.</p><p class="simpara">Default: <code class="literal">localhost</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.defaultBrokerPort</span></dt><dd><p class="simpara"> <code class="literal">brokers</code> allows hosts specified with or without port information (e.g., <code class="literal">host1,host2:port2</code>).
This sets the default port when no port is configured in the broker list.</p><p class="simpara">Default: <code class="literal">9092</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.configuration</span></dt><dd><p class="simpara"> Key/Value map of client properties (both producers and consumer) passed to all clients created by the binder.
Due to the fact that these properties will be used by both producers and consumers, usage should be restricted to common properties, for example, security settings.</p><p class="simpara">Default: Empty map.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.headers</span></dt><dd><p class="simpara"> The list of custom headers that will be transported by the binder.
Only required when communicating with older applications (&#8656; 1.3.x) with a <code class="literal">kafka-clients</code> version &lt; 0.11.0.0; newer versions support headers natively.</p><p class="simpara">Default: empty.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.healthTimeout</span></dt><dd><p class="simpara"> The time to wait to get partition information in seconds; default 60.
Health will report as down if this timer expires.</p><p class="simpara">Default: 10.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.requiredAcks</span></dt><dd><p class="simpara"> The number of required acks on the broker.
See the Kafka documentation for the producer <code class="literal">acks</code> property.</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.minPartitionCount</span></dt><dd><p class="simpara"> Effective only if <code class="literal">autoCreateTopics</code> or <code class="literal">autoAddPartitions</code> is set.
The global minimum number of partitions that the binder will configure on topics on which it produces/consumes data.
It can be superseded by the <code class="literal">partitionCount</code> setting of the producer or by the value of <code class="literal">instanceCount</code> * <code class="literal">concurrency</code> settings of the producer (if either is larger).</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.replicationFactor</span></dt><dd><p class="simpara"> The replication factor of auto-created topics if <code class="literal">autoCreateTopics</code> is active.
Can be overriden on each binding.</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.autoCreateTopics</span></dt><dd><p class="simpara"> If set to <code class="literal">true</code>, the binder will create new topics automatically.
If set to <code class="literal">false</code>, the binder will rely on the topics being already configured.
In the latter case, if the topics do not exist, the binder will fail to start.
Of note, this setting is independent of the <code class="literal">auto.topic.create.enable</code> setting of the broker and it does not influence it: if the server is set to auto-create topics, they may be created as part of the metadata retrieval request, with default broker settings.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.autoAddPartitions</span></dt><dd><p class="simpara"> If set to <code class="literal">true</code>, the binder will create add new partitions if required.
If set to <code class="literal">false</code>, the binder will rely on the partition size of the topic being already configured.
If the partition count of the target topic is smaller than the expected value, the binder will fail to start.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.transaction.transactionIdPrefix</span></dt><dd><p class="simpara">Enable transactions in the binder; see <code class="literal">transaction.id</code> in the Kafka documentation and <a class="link" href="https://docs.spring.io/spring-kafka/reference/html/_reference.html#transactions" target="_top">Transactions</a> in the <code class="literal">spring-kafka</code> documentation.
When transactions are enabled, individual <code class="literal">producer</code> properties are ignored and all producers use the <code class="literal">spring.cloud.stream.kafka.binder.transaction.producer.*</code> properties.</p><p class="simpara">Default <code class="literal">null</code> (no transactions)</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.transaction.producer.*</span></dt><dd><p class="simpara">Global producer properties for producers in a transactional binder.
See <code class="literal">spring.cloud.stream.kafka.binder.transaction.transactionIdPrefix</code> and <a class="xref" href="multi__apache_kafka_binder.html#kafka-producer-properties" title="39.3.3&nbsp;Kafka Producer Properties">Section&nbsp;39.3.3, &#8220;Kafka Producer Properties&#8221;</a> and the general producer properties supported by all binders.</p><p class="simpara">Default: See individual producer properties.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.headerMapperBeanName</span></dt><dd><p class="simpara"> The bean name of a <code class="literal">KafkaHeaderMapper</code> used for mapping <code class="literal">spring-messaging</code> headers to/from Kafka headers.
Use this, for example, if you wish to customize the trusted packages in a <code class="literal">DefaultKafkaHeaderMapper</code>, which uses JSON deserialization for the headers.</p><p class="simpara">Default: none.</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="kafka-consumer-properties" href="#kafka-consumer-properties"></a>39.3.2&nbsp;Kafka Consumer Properties</h3></div></div></div><p>The following properties are available for Kafka consumers only and
must be prefixed with <code class="literal">spring.cloud.stream.kafka.bindings.&lt;channelName&gt;.consumer.</code>.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">admin.configuration</span></dt><dd><p class="simpara">A <code class="literal">Map</code> of Kafka topic properties used when provisioning topics.
e.g. <code class="literal">spring.cloud.stream.kafka.bindings.input.consumer.admin.configuration.message.format.version=0.9.0.0</code></p><p class="simpara">Default: none.</p></dd><dt><span class="term">admin.replicas-assignment</span></dt><dd><p class="simpara">A Map&lt;Integer, List&lt;Integer&gt;&gt; of replica assignments, with the key being the partition and value the assignments.
Used when provisioning new topics.
See <code class="literal">NewTopic</code> javadocs in the <code class="literal">kafka-clients</code> jar.</p><p class="simpara">Default: none.</p></dd><dt><span class="term">admin.replication-factor</span></dt><dd><p class="simpara">The replication factor to use when provisioning topics; overrides the binder-wide setting.
Ignored if <code class="literal">replicas-assignments</code> is present.</p><p class="simpara">Default: none (the binder-wide default of 1 is used).</p></dd><dt><span class="term">autoRebalanceEnabled</span></dt><dd><p class="simpara">When <code class="literal">true</code>, topic partitions will be automatically rebalanced between the members of a consumer group.
When <code class="literal">false</code>, each consumer will be assigned a fixed set of partitions based on <code class="literal">spring.cloud.stream.instanceCount</code> and <code class="literal">spring.cloud.stream.instanceIndex</code>.
This requires both <code class="literal">spring.cloud.stream.instanceCount</code> and <code class="literal">spring.cloud.stream.instanceIndex</code> properties to be set appropriately on each launched instance.
The property <code class="literal">spring.cloud.stream.instanceCount</code> must typically be greater than 1 in this case.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">ackEachRecord</span></dt><dd><p class="simpara"> When <code class="literal">autoCommitOffset</code> is <code class="literal">true</code>, whether to commit the offset after each record is processed.
By default, offsets are committed after all records in the batch of records returned by <code class="literal">consumer.poll()</code> have been processed.
The number of records returned by a poll can be controlled with the <code class="literal">max.poll.recods</code> Kafka property, set via the consumer <code class="literal">configuration</code> property.
Setting this to true may cause a degradation in performance, but reduces the likelihood of redelivered records when a failure occurs.
Also see the binder <code class="literal">requiredAcks</code> property, which also affects the performance of committing offsets.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">autoCommitOffset</span></dt><dd><p class="simpara"> Whether to autocommit offsets when a message has been processed.
If set to <code class="literal">false</code>, a header with the key <code class="literal">kafka_acknowledgment</code> of the type <code class="literal">org.springframework.kafka.support.Acknowledgment</code> header will be present in the inbound message.
Applications may use this header for acknowledging messages.
See the examples section for details.
When this property is set to <code class="literal">false</code>, Kafka binder will set the ack mode to <code class="literal">org.springframework.kafka.listener.AbstractMessageListenerContainer.AckMode.MANUAL</code> and the application is responsible for acknowledging records.
Also see <code class="literal">ackEachRecord</code>.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">autoCommitOnError</span></dt><dd><p class="simpara"> Effective only if <code class="literal">autoCommitOffset</code> is set to <code class="literal">true</code>.
If set to <code class="literal">false</code> it suppresses auto-commits for messages that result in errors, and will commit only for successful messages, allows a stream to automatically replay from the last successfully processed message, in case of persistent failures.
If set to <code class="literal">true</code>, it will always auto-commit (if auto-commit is enabled).
If not set (default), it effectively has the same value as <code class="literal">enableDlq</code>, auto-committing erroneous messages if they are sent to a DLQ, and not committing them otherwise.</p><p class="simpara">Default: not set.</p></dd><dt><span class="term">resetOffsets</span></dt><dd><p class="simpara">Whether to reset offsets on the consumer to the value provided by startOffset.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">startOffset</span></dt><dd><p class="simpara"> The starting offset for new groups.
Allowed values: <code class="literal">earliest</code>, <code class="literal">latest</code>.
If the consumer group is set explicitly for the consumer 'binding' (via <code class="literal">spring.cloud.stream.bindings.&lt;channelName&gt;.group</code>), then 'startOffset' is set to <code class="literal">earliest</code>; otherwise it is set to <code class="literal">latest</code> for the <code class="literal">anonymous</code> consumer group.
Also see <code class="literal">resetOffsets</code>.</p><p class="simpara">Default: null (equivalent to <code class="literal">earliest</code>).</p></dd><dt><span class="term">enableDlq</span></dt><dd><p class="simpara">When set to true, it will send enable DLQ behavior for the consumer.
By default, messages that result in errors will be forwarded to a topic named <code class="literal">error.&lt;destination&gt;.&lt;group&gt;</code>.
The DLQ topic name can be configurable via the property <code class="literal">dlqName</code>.
This provides an alternative option to the more common Kafka replay scenario for the case when the number of errors is relatively small and replaying the entire original topic may be too cumbersome.
See <a class="xref" href="multi__apache_kafka_binder.html#kafka-dlq-processing" title="39.6&nbsp;Dead-Letter Topic Processing">Section&nbsp;39.6, &#8220;Dead-Letter Topic Processing&#8221;</a> processing for more information.
Starting with <span class="emphasis"><em>version 2.0</em></span>, messages sent to the DLQ topic are enhanced with the following headers: <code class="literal">x-original-topic</code>, <code class="literal">x-exception-message</code> and <code class="literal">x-exception-stacktrace</code> as <code class="literal">byte[]</code>.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">configuration</span></dt><dd><p class="simpara">Map with a key/value pair containing generic Kafka consumer properties.</p><p class="simpara">Default: Empty map.</p></dd><dt><span class="term">dlqName</span></dt><dd><p class="simpara">The name of the DLQ topic to receive the error messages.</p><p class="simpara">Default: null (If not specified, messages that result in errors will be forwarded to a topic named <code class="literal">error.&lt;destination&gt;.&lt;group&gt;</code>).</p></dd><dt><span class="term">dlqProducerProperties</span></dt><dd><p class="simpara">Using this, dlq specific producer properties can be set.
All the properties available through kafka producer properties can be set through this property.</p><p class="simpara">Default: Default Kafka producer properties.</p></dd><dt><span class="term">standardHeaders</span></dt><dd><p class="simpara">Indicates which standard headers are populated by the inbound channel adapter.
<code class="literal">none</code>, <code class="literal">id</code>, <code class="literal">timestamp</code> or <code class="literal">both</code>.
Useful if using native deserialization and the first component to receive a message needs an <code class="literal">id</code> (such as an aggregator that is configured to use a JDBC message store).</p><p class="simpara">Default: <code class="literal">none</code></p></dd><dt><span class="term">converterBeanName</span></dt><dd><p class="simpara">The name of a bean that implements <code class="literal">RecordMessageConverter</code>; used in the inbound channel adapter to replace the default <code class="literal">MessagingMessageConverter</code>.</p><p class="simpara">Default: <code class="literal">null</code></p></dd><dt><span class="term">idleEventInterval</span></dt><dd><p class="simpara">The interval, in milliseconds between events indicating that no messages have recently been received.
Use an <code class="literal">ApplicationListener&lt;ListenerContainerIdleEvent&gt;</code> to receive these events.
See <a class="xref" href="multi__apache_kafka_binder.html#pause-resume" title="Example: Pausing and Resuming the Consumer">the section called &#8220;Example: Pausing and Resuming the Consumer&#8221;</a> for a usage example.</p><p class="simpara">Default: <code class="literal">30000</code></p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="kafka-producer-properties" href="#kafka-producer-properties"></a>39.3.3&nbsp;Kafka Producer Properties</h3></div></div></div><p>The following properties are available for Kafka producers only and
must be prefixed with <code class="literal">spring.cloud.stream.kafka.bindings.&lt;channelName&gt;.producer.</code>.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">admin.configuration</span></dt><dd><p class="simpara">A <code class="literal">Map</code> of Kafka topic properties used when provisioning new topics.
e.g. <code class="literal">spring.cloud.stream.kafka.bindings.input.consumer.admin.configuration.message.format.version=0.9.0.0</code></p><p class="simpara">Default: none.</p></dd><dt><span class="term">admin.replicas-assignment</span></dt><dd><p class="simpara">A Map&lt;Integer, List&lt;Integer&gt;&gt; of replica assignments, with the key being the partition and value the assignments.
Used when provisioning new topics.
See <code class="literal">NewTopic</code> javadocs in the <code class="literal">kafka-clients</code> jar.</p><p class="simpara">Default: none.</p></dd><dt><span class="term">admin.replication-factor</span></dt><dd><p class="simpara">The replication factor to use when provisioning new topics; overrides the binder-wide setting.
Ignored if <code class="literal">replicas-assignments</code> is present.</p><p class="simpara">Default: none (the binder-wide default of 1 is used).</p></dd><dt><span class="term">bufferSize</span></dt><dd><p class="simpara">Upper limit, in bytes, of how much data the Kafka producer will attempt to batch before sending.</p><p class="simpara">Default: <code class="literal">16384</code>.</p></dd><dt><span class="term">sync</span></dt><dd><p class="simpara">Whether the producer is synchronous.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">batchTimeout</span></dt><dd><p class="simpara"> How long the producer will wait before sending in order to allow more messages to accumulate in the same batch.
(Normally the producer does not wait at all, and simply sends all the messages that accumulated while the previous send was in progress.) A non-zero value may increase throughput at the expense of latency.</p><p class="simpara">Default: <code class="literal">0</code>.</p></dd><dt><span class="term">messageKeyExpression</span></dt><dd><p class="simpara"> A SpEL expression evaluated against the outgoing message used to populate the key of the produced Kafka message.
For example <code class="literal">headers['myKey']</code>; the payload cannot be used because by the time this expression is evaluated, the payload is already in the form of a <code class="literal">byte[]</code>.</p><p class="simpara">Default: <code class="literal">none</code>.</p></dd><dt><span class="term">headerPatterns</span></dt><dd><p class="simpara"> A comma-delimited list of simple patterns to match spring-messaging headers to be mapped to the kafka <code class="literal">Headers</code> in the <code class="literal">ProducerRecord</code>.
Patterns can begin or end with the wildcard character (asterisk).
Patterns can be negated by prefixing with <code class="literal">!</code>; matching stops after the first match (positive or negative).
For example <code class="literal">!foo,fo*</code> will pass <code class="literal">fox</code> but not <code class="literal">foo</code>.
<code class="literal">id</code> and <code class="literal">timestamp</code> are never mapped.</p><p class="simpara">Default: <code class="literal">*</code> (all headers - except the <code class="literal">id</code> and <code class="literal">timestamp</code>)</p></dd><dt><span class="term">configuration</span></dt><dd><p class="simpara">Map with a key/value pair containing generic Kafka producer properties.</p><p class="simpara">Default: Empty map.</p></dd></dl></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The Kafka binder will use the <code class="literal">partitionCount</code> setting of the producer as a hint to create a topic with the given partition count (in conjunction with the <code class="literal">minPartitionCount</code>, the maximum of the two being the value being used).
Exercise caution when configuring both <code class="literal">minPartitionCount</code> for a binder and <code class="literal">partitionCount</code> for an application, as the larger value will be used.
If a topic already exists with a smaller partition count and <code class="literal">autoAddPartitions</code> is disabled (the default), then the binder will fail to start.
If a topic already exists with a smaller partition count and <code class="literal">autoAddPartitions</code> is enabled, new partitions will be added.
If a topic already exists with a larger number of partitions than the maximum of (<code class="literal">minPartitionCount</code> and <code class="literal">partitionCount</code>), the existing partition count will be used.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_usage_examples" href="#_usage_examples"></a>39.3.4&nbsp;Usage examples</h3></div></div></div><p>In this section, we illustrate the use of the above properties for specific scenarios.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="_example_setting_literal_autocommitoffset_literal_false_and_relying_on_manual_acking" href="#_example_setting_literal_autocommitoffset_literal_false_and_relying_on_manual_acking"></a>Example: Setting <code class="literal">autoCommitOffset</code> false and relying on manual acking.</h4></div></div></div><p>This example illustrates how one may manually acknowledge offsets in a consumer application.</p><p>This example requires that <code class="literal">spring.cloud.stream.kafka.bindings.input.consumer.autoCommitOffset</code> is set to false.
Use the corresponding input channel name for your example.</p><pre class="screen">@SpringBootApplication
@EnableBinding(Sink.class)
public class ManuallyAcknowdledgingConsumer {
public static void main(String[] args) {
SpringApplication.run(ManuallyAcknowdledgingConsumer.class, args);
}
@StreamListener(Sink.INPUT)
public void process(Message&lt;?&gt; message) {
Acknowledgment acknowledgment = message.getHeaders().get(KafkaHeaders.ACKNOWLEDGMENT, Acknowledgment.class);
if (acknowledgment != null) {
System.out.println("Acknowledgment provided");
acknowledgment.acknowledge();
}
}
}</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="_example_security_configuration" href="#_example_security_configuration"></a>Example: security configuration</h4></div></div></div><p>Apache Kafka 0.9 supports secure connections between client and brokers.
To take advantage of this feature, follow the guidelines in the <a class="link" href="http://kafka.apache.org/090/documentation.html#security_configclients" target="_top">Apache Kafka Documentation</a> as well as the Kafka 0.9 <a class="link" href="http://docs.confluent.io/2.0.0/kafka/security.html" target="_top">security guidelines from the Confluent documentation</a>.
Use the <code class="literal">spring.cloud.stream.kafka.binder.configuration</code> option to set security properties for all clients created by the binder.</p><p>For example, for setting <code class="literal">security.protocol</code> to <code class="literal">SASL_SSL</code>, set:</p><pre class="screen">spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_SSL</pre><p>All the other security properties can be set in a similar manner.</p><p>When using Kerberos, follow the instructions in the <a class="link" href="http://kafka.apache.org/090/documentation.html#security_sasl_clientconfig" target="_top">reference documentation</a> for creating and referencing the JAAS configuration.</p><p>Spring Cloud Stream supports passing JAAS configuration information to the application using a JAAS configuration file and using Spring Boot properties.</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="_using_jaas_configuration_files" href="#_using_jaas_configuration_files"></a>Using JAAS configuration files</h5></div></div></div><p>The JAAS, and (optionally) krb5 file locations can be set for Spring Cloud Stream applications by using system properties.
Here is an example of launching a Spring Cloud Stream application with SASL and Kerberos using a JAAS configuration file:</p><pre class="screen"> java -Djava.security.auth.login.config=/path.to/kafka_client_jaas.conf -jar log.jar \
--spring.cloud.stream.kafka.binder.brokers=secure.server:9092 \
--spring.cloud.stream.bindings.input.destination=stream.ticktock \
--spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_PLAINTEXT</pre></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="_using_spring_boot_properties" href="#_using_spring_boot_properties"></a>Using Spring Boot properties</h5></div></div></div><p>As an alternative to having a JAAS configuration file, Spring Cloud Stream provides a mechanism for setting up the JAAS configuration for Spring Cloud Stream applications using Spring Boot properties.</p><p>The following properties can be used for configuring the login context of the Kafka client.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.loginModule</span></dt><dd><p class="simpara">The login module name. Not necessary to be set in normal cases.</p><p class="simpara">Default: <code class="literal">com.sun.security.auth.module.Krb5LoginModule</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.controlFlag</span></dt><dd><p class="simpara">The control flag of the login module.</p><p class="simpara">Default: <code class="literal">required</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.options</span></dt><dd><p class="simpara">Map with a key/value pair containing the login module options.</p><p class="simpara">Default: Empty map.</p></dd></dl></div><p>Here is an example of launching a Spring Cloud Stream application with SASL and Kerberos using Spring Boot configuration properties:</p><pre class="screen"> java --spring.cloud.stream.kafka.binder.brokers=secure.server:9092 \
--spring.cloud.stream.bindings.input.destination=stream.ticktock \
--spring.cloud.stream.kafka.binder.autoCreateTopics=false \
--spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_PLAINTEXT \
--spring.cloud.stream.kafka.binder.jaas.options.useKeyTab=true \
--spring.cloud.stream.kafka.binder.jaas.options.storeKey=true \
--spring.cloud.stream.kafka.binder.jaas.options.keyTab=/etc/security/keytabs/kafka_client.keytab \
--spring.cloud.stream.kafka.binder.jaas.options.principal=kafka-client-1@EXAMPLE.COM</pre><p>This represents the equivalent of the following JAAS file:</p><pre class="screen">KafkaClient {
com.sun.security.auth.module.Krb5LoginModule required
useKeyTab=true
storeKey=true
keyTab="/etc/security/keytabs/kafka_client.keytab"
principal="kafka-client-1@EXAMPLE.COM";
};</pre><p>If the topics required already exist on the broker, or will be created by an administrator, autocreation can be turned off and only client JAAS properties need to be sent.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Do not mix JAAS configuration files and Spring Boot properties in the same application.
If the <code class="literal">-Djava.security.auth.login.config</code> system property is already present, Spring Cloud Stream will ignore the Spring Boot properties.</p></td></tr></table></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Exercise caution when using the <code class="literal">autoCreateTopics</code> and <code class="literal">autoAddPartitions</code> if using Kerberos.
Usually applications may use principals that do not have administrative rights in Kafka and Zookeeper, and relying on Spring Cloud Stream to create/modify topics may fail.
In secure environments, we strongly recommend creating topics and managing ACLs administratively using Kafka tooling.</p></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="pause-resume" href="#pause-resume"></a>Example: Pausing and Resuming the Consumer</h4></div></div></div><p>If you wish to suspend consumption, but not cause a partition rebalance, you can pause and resume the consumer.
This is facilitated by adding the <code class="literal">Consumer</code> as a parameter to your <code class="literal">@StreamListener</code>.
To resume, you need an <code class="literal">ApplicationListener</code> for <code class="literal">ListenerContainerIdleEvent</code> s; the frequency at which events are published is controlled by the <code class="literal">idleEventInterval</code> property.
Since the consumer is not thread-safe, you must call these methods on the calling thread.</p><p>The following simple application shows how to pause and resume.</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableBinding(Sink.class)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> Application {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
SpringApplication.run(Application.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>, args);
}
<em><span class="hl-annotation" style="color: gray">@StreamListener(Sink.INPUT)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> in(String in, <em><span class="hl-annotation" style="color: gray">@Header(KafkaHeaders.CONSUMER)</span></em> Consumer&lt;?, ?&gt; consumer) {
System.out.println(in);
consumer.pause(Collections.singleton(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> TopicPartition(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"myTopic"</span>, <span class="hl-number">0</span>)));
}
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> ApplicationListener&lt;ListenerContainerIdleEvent&gt; idleListener() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> event -&gt; {
System.out.println(event);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (event.getConsumer().paused().size() &gt; <span class="hl-number">0</span>) {
event.getConsumer().resume(event.getConsumer().paused());
}
};
}
}</pre></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-error-channels" href="#kafka-error-channels"></a>39.4&nbsp;Error Channels</h2></div></div></div><p>Starting with <span class="emphasis"><em>version 1.3</em></span>, the binder unconditionally sends exceptions to an error channel for each consumer destination, and can be configured to send async producer send failures to an error channel too.
See <a class="xref" href="multi__programming_model.html#binder-error-channels" title="Message Channel Binders and Error Channels">the section called &#8220;Message Channel Binders and Error Channels&#8221;</a> for more information.</p><p>The payload of the <code class="literal">ErrorMessage</code> for a send failure is a <code class="literal">KafkaSendFailureException</code> with properties:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">failedMessage</code> - the spring-messaging <code class="literal">Message&lt;?&gt;</code> that failed to be sent.</li><li class="listitem"><code class="literal">record</code> - the raw <code class="literal">ProducerRecord</code> that was created from the <code class="literal">failedMessage</code></li></ul></div><p>There is no automatic handling of producer exceptions (such as sending to a <a class="link" href="multi__apache_kafka_binder.html#kafka-dlq-processing" title="39.6&nbsp;Dead-Letter Topic Processing">Dead-Letter queue</a>); you can consume these exceptions with your own Spring Integration flow.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-metrics" href="#kafka-metrics"></a>39.5&nbsp;Kafka Metrics</h2></div></div></div><p>Kafka binder module exposes the following metrics:</p><p><code class="literal">spring.cloud.stream.binder.kafka.someGroup.someTopic.lag</code> - this metric indicates how many messages have not been yet consumed from given binder&#8217;s topic by given consumer group.
For example if the value of the metric <code class="literal">spring.cloud.stream.binder.kafka.myGroup.myTopic.lag</code> is <code class="literal">1000</code>, then consumer group <code class="literal">myGroup</code> has <code class="literal">1000</code> messages to waiting to be consumed from topic <code class="literal">myTopic</code>.
This metric is particularly useful to provide auto-scaling feedback to PaaS platform of your choice.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-dlq-processing" href="#kafka-dlq-processing"></a>39.6&nbsp;Dead-Letter Topic Processing</h2></div></div></div><p>Because it can&#8217;t be anticipated how users would want to dispose of dead-lettered messages, the framework does not provide any standard mechanism to handle them.
If the reason for the dead-lettering is transient, you may wish to route the messages back to the original topic.
However, if the problem is a permanent issue, that could cause an infinite loop.
The following <code class="literal">spring-boot</code> application is an example of how to route those messages back to the original topic, but moves them to a third "parking lot" topic after three attempts.
The application is simply another spring-cloud-stream application that reads from the dead-letter topic.
It terminates when no messages are received for 5 seconds.</p><p>The examples assume the original destination is <code class="literal">so8400out</code> and the consumer group is <code class="literal">so8400</code>.</p><p>There are several considerations.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Consider only running the rerouting when the main application is not running.
Otherwise, the retries for transient errors will be used up very quickly.</li><li class="listitem">Alternatively, use a two-stage approach - use this application to route to a third topic, and another to route from there back to the main topic.</li><li class="listitem">Since this technique uses a message header to keep track of retries, it won&#8217;t work with <code class="literal">headerMode=raw</code>.
In that case, consider adding some data to the payload (that can be ignored by the main application).</li><li class="listitem"><code class="literal">x-retries</code> has to be added to the <code class="literal">headers</code> property <code class="literal">spring.cloud.stream.kafka.binder.headers=x-retries</code> on both this, and the main application so that the header is transported between the applications.</li><li class="listitem">Since kafka is publish/subscribe, replayed messages will be sent to each consumer group, even those that successfully processed a message the first time around.</li></ul></div><p><b>application.properties.&nbsp;</b>
</p><pre class="screen">spring.cloud.stream.bindings.input.group=so8400replay
spring.cloud.stream.bindings.input.destination=error.so8400out.so8400
spring.cloud.stream.bindings.output.destination=so8400out
spring.cloud.stream.bindings.output.producer.partitioned=true
spring.cloud.stream.bindings.parkingLot.destination=so8400in.parkingLot
spring.cloud.stream.bindings.parkingLot.producer.partitioned=true
spring.cloud.stream.kafka.binder.configuration.auto.offset.reset=earliest
spring.cloud.stream.kafka.binder.headers=x-retries</pre><p>
</p><p><b>Application.&nbsp;</b>
</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableBinding(TwoOutputProcessor.class)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> ReRouteDlqKApplication <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">implements</span> CommandLineRunner {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> String X_RETRIES_HEADER = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"x-retries"</span>;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
SpringApplication.run(ReRouteDlqKApplication.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>, args).close();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> AtomicInteger processed = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> AtomicInteger();
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> MessageChannel parkingLot;
<em><span class="hl-annotation" style="color: gray">@StreamListener(Processor.INPUT)</span></em>
<em><span class="hl-annotation" style="color: gray">@SendTo(Processor.OUTPUT)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Message&lt;?&gt; reRoute(Message&lt;?&gt; failed) {
processed.incrementAndGet();
Integer retries = failed.getHeaders().get(X_RETRIES_HEADER, Integer.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (retries == null) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"First retry for "</span> + failed);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> MessageBuilder.fromMessage(failed)
.setHeader(X_RETRIES_HEADER, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> Integer(<span class="hl-number">1</span>))
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (retries.intValue() &lt; <span class="hl-number">3</span>) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Another retry for "</span> + failed);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> MessageBuilder.fromMessage(failed)
.setHeader(X_RETRIES_HEADER, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> Integer(retries.intValue() + <span class="hl-number">1</span>))
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Retries exhausted for "</span> + failed);
parkingLot.send(MessageBuilder.fromMessage(failed)
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build());
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> null;
}
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> run(String... args) <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throws</span> Exception {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">while</span> (true) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">int</span> count = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.processed.get();
Thread.sleep(<span class="hl-number">5000</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (count == <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.processed.get()) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Idle, terminating"</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span>;
}
}
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">interface</span> TwoOutputProcessor <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> Processor {
<em><span class="hl-annotation" style="color: gray">@Output("parkingLot")</span></em>
MessageChannel parkingLot();
}
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_partitioning_with_the_kafka_binder" href="#_partitioning_with_the_kafka_binder"></a>39.7&nbsp;Partitioning with the Kafka Binder</h2></div></div></div><p>Apache Kafka supports topic partitioning natively.</p><p>Sometimes it is advantageous to send data to specific partitions, for example when you want to strictly order message processing - all messages for a particular customer should go to the same partition.</p><p>The following illustrates how to configure the producer and consumer side:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableBinding(Source.class)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> KafkaPartitionProducerApplication {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> Random RANDOM = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> Random(System.currentTimeMillis());
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> String[] data = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> String[] {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"foo1"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"bar1"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"qux1"</span>,
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"foo2"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"bar2"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"qux2"</span>,
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"foo3"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"bar3"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"qux3"</span>,
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"foo4"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"bar4"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"qux4"</span>,
};
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> SpringApplicationBuilder(KafkaPartitionProducerApplication.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>)
.web(false)
.run(args);
}
<em><span class="hl-annotation" style="color: gray">@InboundChannelAdapter(channel = Source.OUTPUT, poller = @Poller(fixedRate = "5000"))</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Message&lt;?&gt; generate() {
String value = data[RANDOM.nextInt(data.length)];
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Sending: "</span> + value);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> MessageBuilder.withPayload(value)
.setHeader(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"partitionKey"</span>, value)
.build();
}
}</pre><p><b>application.yml.&nbsp;</b>
</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute">spring</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> cloud</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> stream</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> bindings</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> output</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> destination</span>: partitioned.topic
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> producer</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> partitioned</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">true</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> partition-key-expression</span>: headers[<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">'partitionKey'</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">]</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> partition-count</span>: <span class="hl-number">12</span></pre><p>
</p><div class="important" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Important"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="images/important.png"></td><th align="left">Important</th></tr><tr><td align="left" valign="top"><p>The topic must be provisioned to have enough partitions to achieve the desired concurrency for all consumer groups.
The above configuration will support up to 12 consumer instances (or 6 if their <code class="literal">concurrency</code> is 2, etc.).
It is generally best to "over provision" the partitions to allow for future increases in consumers and/or concurrency.</p></td></tr></table></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The above configuration uses the default partitioning (<code class="literal">key.hashCode() % partitionCount</code>).
This may or may not provide a suitably balanced algorithm, depending on the key values; you can override this default by using the <code class="literal">partitionSelectorExpression</code> or <code class="literal">partitionSelectorClass</code> properties.</p></td></tr></table></div><p>Since partitions are natively handled by Kafka, no special configuration is needed on the consumer side.
Kafka will allocate partitions across the instances.</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableBinding(Sink.class)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> KafkaPartitionConsumerApplication {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> SpringApplicationBuilder(KafkaPartitionConsumerApplication.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>)
.web(false)
.run(args);
}
<em><span class="hl-annotation" style="color: gray">@StreamListener(Sink.INPUT)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> listen(<em><span class="hl-annotation" style="color: gray">@Payload</span></em> String in, <em><span class="hl-annotation" style="color: gray">@Header(KafkaHeaders.RECEIVED_PARTITION_ID)</span></em> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">int</span> partition) {
System.out.println(in + <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">" received from partition "</span> + partition);
}
}</pre><p><b>application.yml.&nbsp;</b>
</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute">spring</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> cloud</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> stream</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> bindings</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> input</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> destination</span>: partitioned.topic
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> group</span>: myGroup</pre><p>
</p><p>You can add instances as needed; Kafka will rebalance the partition allocations.
If the instance count (or <code class="literal">instance count * concurrency</code>) exceeds the number of partitions, some consumers will be idle.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__binder_implementations.html">Prev</a>&nbsp;</td><td width="20%" align="center"><a accesskey="u" href="multi__binder_implementations.html">Up</a></td><td width="40%" align="right">&nbsp;<a accesskey="n" href="multi__apache_kafka_streams_binder.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part&nbsp;VI.&nbsp;Binder Implementations&nbsp;</td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud.html">Home</a></td><td width="40%" align="right" valign="top">&nbsp;40.&nbsp;Apache Kafka Streams Binder</td></tr></table></div></body></html>
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