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<h1 class="page-title">Storm Kafka Integration</h1>
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<p>Provides core Storm and Trident spout implementations for consuming data from Apache Kafka 0.8.x.</p>
<h2 id="spouts">Spouts</h2>
<p>We support both Trident and core Storm spouts. For both spout implementations, we use a BrokerHost interface that
tracks Kafka broker host to partition mapping and kafkaConfig that controls some Kafka related parameters.</p>
<h3 id="brokerhosts">BrokerHosts</h3>
<p>In order to initialize your Kafka spout/emitter you need to construct an instance of the marker interface BrokerHosts.
Currently, we support the following two implementations:</p>
<h4 id="zkhosts">ZkHosts</h4>
<p>ZkHosts is what you should use if you want to dynamically track Kafka broker to partition mapping. This class uses
Kafka&#39;s ZooKeeper entries to track brokerHost -&gt; partition mapping. You can instantiate an object by calling
<code>java
public ZkHosts(String brokerZkStr, String brokerZkPath)
public ZkHosts(String brokerZkStr)
</code>
Where brokerZkStr is just ip:port (e.g. localhost:2181). brokerZkPath is the root directory under which all the topics and
partition information is stored. By default this is /brokers which is what the default Kafka implementation uses.</p>
<p>By default, the broker-partition mapping is refreshed every 60 seconds from ZooKeeper. If you want to change it, you
should set host.refreshFreqSecs to your chosen value.</p>
<h4 id="statichosts">StaticHosts</h4>
<p>This is an alternative implementation where broker -&gt; partition information is static. In order to construct an instance
of this class, you need to first construct an instance of GlobalPartitionInformation.</p>
<div class="highlight"><pre><code class="language-java" data-lang="java"> <span class="n">Broker</span> <span class="n">brokerForPartition0</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Broker</span><span class="o">(</span><span class="s">"localhost"</span><span class="o">);</span><span class="c1">//localhost:9092</span>
<span class="n">Broker</span> <span class="n">brokerForPartition1</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Broker</span><span class="o">(</span><span class="s">"localhost"</span><span class="o">,</span> <span class="mi">9092</span><span class="o">);</span><span class="c1">//localhost:9092 but we specified the port explicitly</span>
<span class="n">Broker</span> <span class="n">brokerForPartition2</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Broker</span><span class="o">(</span><span class="s">"localhost:9092"</span><span class="o">);</span><span class="c1">//localhost:9092 specified as one string.</span>
<span class="n">GlobalPartitionInformation</span> <span class="n">partitionInfo</span> <span class="o">=</span> <span class="k">new</span> <span class="n">GlobalPartitionInformation</span><span class="o">();</span>
<span class="n">partitionInfo</span><span class="o">.</span><span class="na">addPartition</span><span class="o">(</span><span class="mi">0</span><span class="o">,</span> <span class="n">brokerForPartition0</span><span class="o">);</span><span class="c1">//mapping from partition 0 to brokerForPartition0</span>
<span class="n">partitionInfo</span><span class="o">.</span><span class="na">addPartition</span><span class="o">(</span><span class="mi">1</span><span class="o">,</span> <span class="n">brokerForPartition1</span><span class="o">);</span><span class="c1">//mapping from partition 1 to brokerForPartition1</span>
<span class="n">partitionInfo</span><span class="o">.</span><span class="na">addPartition</span><span class="o">(</span><span class="mi">2</span><span class="o">,</span> <span class="n">brokerForPartition2</span><span class="o">);</span><span class="c1">//mapping from partition 2 to brokerForPartition2</span>
<span class="n">StaticHosts</span> <span class="n">hosts</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StaticHosts</span><span class="o">(</span><span class="n">partitionInfo</span><span class="o">);</span>
</code></pre></div>
<h3 id="kafkaconfig">KafkaConfig</h3>
<p>The second thing needed for constructing a kafkaSpout is an instance of KafkaConfig.
<code>java
public KafkaConfig(BrokerHosts hosts, String topic)
public KafkaConfig(BrokerHosts hosts, String topic, String clientId)
</code></p>
<p>The BrokerHosts can be any implementation of BrokerHosts interface as described above. The topic is name of Kafka topic.
The optional ClientId is used as a part of the ZooKeeper path where the spout&#39;s current consumption offset is stored.</p>
<p>There are 2 extensions of KafkaConfig currently in use.</p>
<p>Spoutconfig is an extension of KafkaConfig that supports additional fields with ZooKeeper connection info and for controlling
behavior specific to KafkaSpout. The Zkroot will be used as root to store your consumer&#39;s offset. The id should uniquely
identify your spout.
<code>java
public SpoutConfig(BrokerHosts hosts, String topic, String zkRoot, String id);
public SpoutConfig(BrokerHosts hosts, String topic, String id);
</code>
In addition to these parameters, SpoutConfig contains the following fields that control how KafkaSpout behaves:
```java
// setting for how often to save the current Kafka offset to ZooKeeper
public long stateUpdateIntervalMs = 2000;</p>
<div class="highlight"><pre><code class="language-" data-lang="">// Exponential back-off retry settings. These are used when retrying messages after a bolt
// calls OutputCollector.fail().
// Note: be sure to set backtype.storm.Config.MESSAGE_TIMEOUT_SECS appropriately to prevent
// resubmitting the message while still retrying.
public long retryInitialDelayMs = 0;
public double retryDelayMultiplier = 1.0;
public long retryDelayMaxMs = 60 * 1000;
// if set to true, spout will set Kafka topic as the emitted Stream ID
public boolean topicAsStreamId = false;
</code></pre></div><div class="highlight"><pre><code class="language-" data-lang="">Core KafkaSpout only accepts an instance of SpoutConfig.
TridentKafkaConfig is another extension of KafkaConfig.
TridentKafkaEmitter only accepts TridentKafkaConfig.
The KafkaConfig class also has bunch of public variables that controls your application's behavior. Here are defaults:
```java
public int fetchSizeBytes = 1024 * 1024;
public int socketTimeoutMs = 10000;
public int fetchMaxWait = 10000;
public int bufferSizeBytes = 1024 * 1024;
public MultiScheme scheme = new RawMultiScheme();
public boolean ignoreZkOffsets = false;
public long startOffsetTime = kafka.api.OffsetRequest.EarliestTime();
public long maxOffsetBehind = Long.MAX_VALUE;
public boolean useStartOffsetTimeIfOffsetOutOfRange = true;
public int metricsTimeBucketSizeInSecs = 60;
</code></pre></div>
<p>Most of them are self explanatory except MultiScheme.</p>
<h3 id="multischeme">MultiScheme</h3>
<p>MultiScheme is an interface that dictates how the byte[] consumed from Kafka gets transformed into a storm tuple. It
also controls the naming of your output field.</p>
<div class="highlight"><pre><code class="language-java" data-lang="java"> <span class="kd">public</span> <span class="n">Iterable</span><span class="o">&lt;</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">&gt;&gt;</span> <span class="n">deserialize</span><span class="o">(</span><span class="kt">byte</span><span class="o">[]</span> <span class="n">ser</span><span class="o">);</span>
<span class="kd">public</span> <span class="n">Fields</span> <span class="n">getOutputFields</span><span class="o">();</span>
</code></pre></div>
<p>The default <code>RawMultiScheme</code> just takes the <code>byte[]</code> and returns a tuple with <code>byte[]</code> as is. The name of the
outputField is &quot;bytes&quot;. There are alternative implementation like <code>SchemeAsMultiScheme</code> and
<code>KeyValueSchemeAsMultiScheme</code> which can convert the <code>byte[]</code> to <code>String</code>.</p>
<h3 id="examples">Examples</h3>
<h4 id="core-spout">Core Spout</h4>
<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="n">BrokerHosts</span> <span class="n">hosts</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ZkHosts</span><span class="o">(</span><span class="n">zkConnString</span><span class="o">);</span>
<span class="n">SpoutConfig</span> <span class="n">spoutConfig</span> <span class="o">=</span> <span class="k">new</span> <span class="n">SpoutConfig</span><span class="o">(</span><span class="n">hosts</span><span class="o">,</span> <span class="n">topicName</span><span class="o">,</span> <span class="s">"/"</span> <span class="o">+</span> <span class="n">topicName</span><span class="o">,</span> <span class="n">UUID</span><span class="o">.</span><span class="na">randomUUID</span><span class="o">().</span><span class="na">toString</span><span class="o">());</span>
<span class="n">spoutConfig</span><span class="o">.</span><span class="na">scheme</span> <span class="o">=</span> <span class="k">new</span> <span class="n">SchemeAsMultiScheme</span><span class="o">(</span><span class="k">new</span> <span class="n">StringScheme</span><span class="o">());</span>
<span class="n">KafkaSpout</span> <span class="n">kafkaSpout</span> <span class="o">=</span> <span class="k">new</span> <span class="n">KafkaSpout</span><span class="o">(</span><span class="n">spoutConfig</span><span class="o">);</span>
</code></pre></div>
<h4 id="trident-spout">Trident Spout</h4>
<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="n">TridentTopology</span> <span class="n">topology</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TridentTopology</span><span class="o">();</span>
<span class="n">BrokerHosts</span> <span class="n">zk</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ZkHosts</span><span class="o">(</span><span class="s">"localhost"</span><span class="o">);</span>
<span class="n">TridentKafkaConfig</span> <span class="n">spoutConf</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TridentKafkaConfig</span><span class="o">(</span><span class="n">zk</span><span class="o">,</span> <span class="s">"test-topic"</span><span class="o">);</span>
<span class="n">spoutConf</span><span class="o">.</span><span class="na">scheme</span> <span class="o">=</span> <span class="k">new</span> <span class="n">SchemeAsMultiScheme</span><span class="o">(</span><span class="k">new</span> <span class="n">StringScheme</span><span class="o">());</span>
<span class="n">OpaqueTridentKafkaSpout</span> <span class="n">spout</span> <span class="o">=</span> <span class="k">new</span> <span class="n">OpaqueTridentKafkaSpout</span><span class="o">(</span><span class="n">spoutConf</span><span class="o">);</span>
</code></pre></div>
<h3 id="how-kafkaspout-stores-offsets-of-a-kafka-topic-and-recovers-in-case-of-failures">How KafkaSpout stores offsets of a Kafka topic and recovers in case of failures</h3>
<p>As shown in the above KafkaConfig properties, you can control from where in the Kafka topic the spout begins to read by
setting <code>KafkaConfig.startOffsetTime</code> as follows:</p>
<ol>
<li><code>kafka.api.OffsetRequest.EarliestTime()</code>: read from the beginning of the topic (i.e. from the oldest messages onwards)</li>
<li><code>kafka.api.OffsetRequest.LatestTime()</code>: read from the end of the topic (i.e. any new messsages that are being written to the topic)</li>
<li>A Unix timestamp aka seconds since the epoch (e.g. via <code>System.currentTimeMillis()</code>):
see <a href="https://cwiki.apache.org/confluence/display/KAFKA/FAQ#FAQ-HowdoIaccuratelygetoffsetsofmessagesforacertaintimestampusingOffsetRequest?">How do I accurately get offsets of messages for a certain timestamp using OffsetRequest?</a> in the Kafka FAQ</li>
</ol>
<p>As the topology runs the Kafka spout keeps track of the offsets it has read and emitted by storing state information
under the ZooKeeper path <code>SpoutConfig.zkRoot+ &quot;/&quot; + SpoutConfig.id</code>. In the case of failures it recovers from the last
written offset in ZooKeeper.</p>
<blockquote>
<p><strong>Important:</strong> When re-deploying a topology make sure that the settings for <code>SpoutConfig.zkRoot</code> and <code>SpoutConfig.id</code>
were not modified, otherwise the spout will not be able to read its previous consumer state information (i.e. the
offsets) from ZooKeeper -- which may lead to unexpected behavior and/or to data loss, depending on your use case.</p>
</blockquote>
<p>This means that when a topology has run once the setting <code>KafkaConfig.startOffsetTime</code> will not have an effect for
subsequent runs of the topology because now the topology will rely on the consumer state information (offsets) in
ZooKeeper to determine from where it should begin (more precisely: resume) reading.
If you want to force the spout to ignore any consumer state information stored in ZooKeeper, then you should
set the parameter <code>KafkaConfig.ignoreZkOffsets</code> to <code>true</code>. If <code>true</code>, the spout will always begin reading from the
offset defined by <code>KafkaConfig.startOffsetTime</code> as described above.</p>
<h2 id="using-storm-kafka-with-different-versions-of-scala">Using storm-kafka with different versions of Scala</h2>
<p>Storm-kafka&#39;s Kafka dependency is defined as <code>provided</code> scope in maven, meaning it will not be pulled in
as a transitive dependency. This allows you to use a version of Kafka built against a specific Scala version.</p>
<p>When building a project with storm-kafka, you must explicitly add the Kafka dependency. For example, to
use Kafka 0.8.1.1 built against Scala 2.10, you would use the following dependency in your <code>pom.xml</code>:</p>
<div class="highlight"><pre><code class="language-xml" data-lang="xml"> <span class="nt">&lt;dependency&gt;</span>
<span class="nt">&lt;groupId&gt;</span>org.apache.kafka<span class="nt">&lt;/groupId&gt;</span>
<span class="nt">&lt;artifactId&gt;</span>kafka_2.10<span class="nt">&lt;/artifactId&gt;</span>
<span class="nt">&lt;version&gt;</span>0.8.1.1<span class="nt">&lt;/version&gt;</span>
<span class="nt">&lt;exclusions&gt;</span>
<span class="nt">&lt;exclusion&gt;</span>
<span class="nt">&lt;groupId&gt;</span>org.apache.zookeeper<span class="nt">&lt;/groupId&gt;</span>
<span class="nt">&lt;artifactId&gt;</span>zookeeper<span class="nt">&lt;/artifactId&gt;</span>
<span class="nt">&lt;/exclusion&gt;</span>
<span class="nt">&lt;exclusion&gt;</span>
<span class="nt">&lt;groupId&gt;</span>log4j<span class="nt">&lt;/groupId&gt;</span>
<span class="nt">&lt;artifactId&gt;</span>log4j<span class="nt">&lt;/artifactId&gt;</span>
<span class="nt">&lt;/exclusion&gt;</span>
<span class="nt">&lt;/exclusions&gt;</span>
<span class="nt">&lt;/dependency&gt;</span>
</code></pre></div>
<p>Note that the ZooKeeper and log4j dependencies are excluded to prevent version conflicts with Storm&#39;s dependencies.</p>
<h2 id="writing-to-kafka-as-part-of-your-topology">Writing to Kafka as part of your topology</h2>
<p>You can create an instance of storm.kafka.bolt.KafkaBolt and attach it as a component to your topology or if you
are using trident you can use storm.kafka.trident.TridentState, storm.kafka.trident.TridentStateFactory and
storm.kafka.trident.TridentKafkaUpdater.</p>
<p>You need to provide implementation of following 2 interfaces</p>
<h3 id="tupletokafkamapper-and-tridenttupletokafkamapper">TupleToKafkaMapper and TridentTupleToKafkaMapper</h3>
<p>These interfaces have 2 methods defined:</p>
<div class="highlight"><pre><code class="language-java" data-lang="java"> <span class="n">K</span> <span class="nf">getKeyFromTuple</span><span class="p">(</span><span class="n">Tuple</span><span class="o">/</span><span class="n">TridentTuple</span> <span class="n">tuple</span><span class="o">);</span>
<span class="n">V</span> <span class="n">getMessageFromTuple</span><span class="o">(</span><span class="n">Tuple</span><span class="o">/</span><span class="n">TridentTuple</span> <span class="n">tuple</span><span class="o">);</span>
</code></pre></div>
<p>As the name suggests, these methods are called to map a tuple to Kafka key and Kafka message. If you just want one field
as key and one field as value, then you can use the provided FieldNameBasedTupleToKafkaMapper.java
implementation. In the KafkaBolt, the implementation always looks for a field with field name &quot;key&quot; and &quot;message&quot; if you
use the default constructor to construct FieldNameBasedTupleToKafkaMapper for backward compatibility
reasons. Alternatively you could also specify a different key and message field by using the non default constructor.
In the TridentKafkaState you must specify what is the field name for key and message as there is no default constructor.
These should be specified while constructing and instance of FieldNameBasedTupleToKafkaMapper.</p>
<h3 id="kafkatopicselector-and-trident-kafkatopicselector">KafkaTopicSelector and trident KafkaTopicSelector</h3>
<p>This interface has only one method
<code>java
public interface KafkaTopicSelector {
String getTopics(Tuple/TridentTuple tuple);
}
</code>
The implementation of this interface should return the topic to which the tuple&#39;s key/message mapping needs to be published
You can return a null and the message will be ignored. If you have one static topic name then you can use
DefaultTopicSelector.java and set the name of the topic in the constructor.</p>
<h3 id="specifying-kafka-producer-properties">Specifying Kafka producer properties</h3>
<p>You can provide all the produce properties , see <a href="http://kafka.apache.org/documentation.html#producerconfigs">http://kafka.apache.org/documentation.html#producerconfigs</a>
section &quot;Important configuration properties for the producer&quot;, in your Storm topology config by setting the properties
map with key kafka.broker.properties.</p>
<h3 id="putting-it-all-together">Putting it all together</h3>
<p>For the bolt :
```java
TopologyBuilder builder = new TopologyBuilder();</p>
<div class="highlight"><pre><code class="language-" data-lang=""> Fields fields = new Fields("key", "message");
FixedBatchSpout spout = new FixedBatchSpout(fields, 4,
new Values("storm", "1"),
new Values("trident", "1"),
new Values("needs", "1"),
new Values("javadoc", "1")
);
spout.setCycle(true);
builder.setSpout("spout", spout, 5);
KafkaBolt bolt = new KafkaBolt()
.withTopicSelector(new DefaultTopicSelector("test"))
.withTupleToKafkaMapper(new FieldNameBasedTupleToKafkaMapper());
builder.setBolt("forwardToKafka", bolt, 8).shuffleGrouping("spout");
Config conf = new Config();
//set producer properties.
Properties props = new Properties();
props.put("metadata.broker.list", "localhost:9092");
props.put("request.required.acks", "1");
props.put("serializer.class", "kafka.serializer.StringEncoder");
conf.put(KafkaBolt.KAFKA_BROKER_PROPERTIES, props);
StormSubmitter.submitTopology("kafkaboltTest", conf, builder.createTopology());
</code></pre></div><div class="highlight"><pre><code class="language-" data-lang="">
For Trident:
```java
Fields fields = new Fields("word", "count");
FixedBatchSpout spout = new FixedBatchSpout(fields, 4,
new Values("storm", "1"),
new Values("trident", "1"),
new Values("needs", "1"),
new Values("javadoc", "1")
);
spout.setCycle(true);
TridentTopology topology = new TridentTopology();
Stream stream = topology.newStream("spout1", spout);
TridentKafkaStateFactory stateFactory = new TridentKafkaStateFactory()
.withKafkaTopicSelector(new DefaultTopicSelector("test"))
.withTridentTupleToKafkaMapper(new FieldNameBasedTupleToKafkaMapper("word", "count"));
stream.partitionPersist(stateFactory, fields, new TridentKafkaUpdater(), new Fields());
Config conf = new Config();
//set producer properties.
Properties props = new Properties();
props.put("metadata.broker.list", "localhost:9092");
props.put("request.required.acks", "1");
props.put("serializer.class", "kafka.serializer.StringEncoder");
conf.put(TridentKafkaState.KAFKA_BROKER_PROPERTIES, props);
StormSubmitter.submitTopology("kafkaTridentTest", conf, topology.build());
</code></pre></div>
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<p>Storm integrates with any queueing system and any database system. Storm's spout abstraction makes it easy to integrate a new queuing system. Likewise, integrating Storm with database systems is easy.</p>
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