Spark Streaming + Kafka Integration Guide

Apache Kafka is publish-subscribe messaging rethought as a distributed, partitioned, replicated commit log service. Here we explain how to configure Spark Streaming to receive data from Kafka.

Linking: In your SBT/Maven project definition, link your streaming application against the following artifact (see Linking section in the main programming guide for further information).
```
 groupId = org.apache.spark
 artifactId = spark-streaming-kafka_2.10
 version = 1.2.1
```
Programming: In the streaming application code, import KafkaUtils and create input DStream as follows.
```
 import org.apache.spark.streaming.kafka._

 val kafkaStream = KafkaUtils.createStream(
 	streamingContext, [zookeeperQuorum], [group id of the consumer], [per-topic number of Kafka partitions to consume])
```
See the API docs and the example.
```
 import org.apache.spark.streaming.kafka.*;

 JavaPairReceiverInputDStream<String, String> kafkaStream = KafkaUtils.createStream(
 	streamingContext, [zookeeperQuorum], [group id of the consumer], [per-topic number of Kafka partitions to consume]);
```
See the API docs and the example.
Points to remember:
- Topic partitions in Kafka does not correlate to partitions of RDDs generated in Spark Streaming. So increasing the number of topic-specific partitions in the KafkaUtils.createStream() only increases the number of threads using which topics that are consumed within a single receiver. It does not increase the parallelism of Spark in processing the data. Refer to the main document for more information on that.
- Multiple Kafka input DStreams can be created with different groups and topics for parallel receiving of data using multiple receivers.
Deploying: Package spark-streaming-kafka_2.10 and its dependencies (except spark-core_2.10 and spark-streaming_2.10 which are provided by spark-submit) into the application JAR. Then use spark-submit to launch your application (see Deploying section in the main programming guide).

Note that the Kafka receiver used by default is an unreliable receiver section in the programming guide). In Spark 1.2, we have added an experimental reliable Kafka receiver that provides stronger fault-tolerance guarantees of zero data loss on failures. This receiver is automatically used when the write ahead log (also introduced in Spark 1.2) is enabled (see Deployment section in the programming guide). This may reduce the receiving throughput of individual Kafka receivers compared to the unreliable receivers, but this can be corrected by running more receivers in parallel to increase aggregate throughput. Additionally, it is recommended that the replication of the received data within Spark be disabled when the write ahead log is enabled as the log is already stored in a replicated storage system. This can be done by setting the storage level for the input stream to StorageLevel.MEMORY_AND_DISK_SER (that is, use KafkaUtils.createStream(..., StorageLevel.MEMORY_AND_DISK_SER)).