scala - Why does Spark application fail with “ClassNotFoundException: Failed to find data source: kafka” as uber-jar with sbt assembly?

Question

I'm trying to run a sample like StructuredKafkaWordCount. I started with the Spark Structured Streaming Programming guide.

My code is

package io.boontadata.spark.job1

import org.apache.spark.sql.SparkSession

object DirectKafkaAggregateEvents {
  val FIELD_MESSAGE_ID = 0
  val FIELD_DEVICE_ID = 1
  val FIELD_TIMESTAMP = 2
  val FIELD_CATEGORY = 3
  val FIELD_MEASURE1 = 4
  val FIELD_MEASURE2 = 5

  def main(args: Array[String]) {
    if (args.length < 3) {
      System.err.println(s"""
        |Usage: DirectKafkaAggregateEvents <brokers> <subscribeType> <topics>
        |  <brokers> is a list of one or more Kafka brokers
        |  <subscribeType> sample value: subscribe
        |  <topics> is a list of one or more kafka topics to consume from
        |
        """.stripMargin)
      System.exit(1)
    }

    val Array(bootstrapServers, subscribeType, topics) = args

    val spark = SparkSession
      .builder
      .appName("boontadata-spark-job1")
      .getOrCreate()

    import spark.implicits._

    // Create DataSet representing the stream of input lines from kafka
    val lines = spark
      .readStream
      .format("kafka")
      .option("kafka.bootstrap.servers", bootstrapServers)
      .option(subscribeType, topics)
      .load()
      .selectExpr("CAST(value AS STRING)")
      .as[String]

    // Generate running word count
    val wordCounts = lines.flatMap(_.split(" ")).groupBy("value").count()

    // Start running the query that prints the running counts to the console
    val query = wordCounts.writeStream
      .outputMode("complete")
      .format("console")
      .start()

    query.awaitTermination()
  }

}

I added the following sbt files:

build.sbt:

name := "boontadata-spark-job1"
version := "0.1"
scalaVersion := "2.11.7"

libraryDependencies += "org.apache.spark" % "spark-core_2.11" % "2.0.2" % "provided"
libraryDependencies += "org.apache.spark" % "spark-streaming_2.11" % "2.0.2" % "provided"
libraryDependencies += "org.apache.spark" % "spark-sql_2.11" % "2.0.2" % "provided"
libraryDependencies += "org.apache.spark" % "spark-sql-kafka-0-10_2.11" % "2.0.2"
libraryDependencies += "org.apache.spark" % "spark-streaming-kafka-0-10_2.11" % "2.0.2"
libraryDependencies += "org.apache.kafka" % "kafka-clients" % "0.10.1.1"
libraryDependencies += "org.apache.kafka" % "kafka_2.11" % "0.10.1.1"

// META-INF discarding
assemblyMergeStrategy in assembly := { 
   {
    case PathList("META-INF", xs @ _*) => MergeStrategy.discard
    case x => MergeStrategy.first
   }
}

I also added project/assembly.sbt

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.3")

This creates a Uber jar with the non provided jars.

I submit with the following line:

spark-submit boontadata-spark-job1-assembly-0.1.jar ks1:9092,ks2:9092,ks3:9092 subscribe sampletopic

but I get this runtime error:

Exception in thread "main" java.lang.ClassNotFoundException: Failed to find data source: kafka. Please find packages at https://cwiki.apache.org/confluence/display/SPARK/Third+Party+Projects
        at org.apache.spark.sql.execution.datasources.DataSource.lookupDataSource(DataSource.scala:148)
        at org.apache.spark.sql.execution.datasources.DataSource.providingClass$lzycompute(DataSource.scala:79)
        at org.apache.spark.sql.execution.datasources.DataSource.providingClass(DataSource.scala:79)
        at org.apache.spark.sql.execution.datasources.DataSource.sourceSchema(DataSource.scala:218)
        at org.apache.spark.sql.execution.datasources.DataSource.sourceInfo$lzycompute(DataSource.scala:80)
        at org.apache.spark.sql.execution.datasources.DataSource.sourceInfo(DataSource.scala:80)
        at org.apache.spark.sql.execution.streaming.StreamingRelation$.apply(StreamingRelation.scala:30)
        at org.apache.spark.sql.streaming.DataStreamReader.load(DataStreamReader.scala:124)
        at io.boontadata.spark.job1.DirectKafkaAggregateEvents$.main(StreamingJob.scala:41)
        at io.boontadata.spark.job1.DirectKafkaAggregateEvents.main(StreamingJob.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:736)
        at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:185)
        at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:210)
        at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:124)
        at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
Caused by: java.lang.ClassNotFoundException: kafka.DefaultSource
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$5$$anonfun$apply$1.apply(DataSource.scala:132)
        at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$5$$anonfun$apply$1.apply(DataSource.scala:132)
        at scala.util.Try$.apply(Try.scala:192)
        at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$5.apply(DataSource.scala:132)
        at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$5.apply(DataSource.scala:132)
        at scala.util.Try.orElse(Try.scala:84)
        at org.apache.spark.sql.execution.datasources.DataSource.lookupDataSource(DataSource.scala:132)
        ... 18 more
16/12/23 13:32:48 INFO spark.SparkContext: Invoking stop() from shutdown hook

Is there a way to know which class is not found so that I can search the maven.org repo for that class.

The lookupDataSource source code seems to be at line 543 at https://github.com/apache/spark/blob/83a6ace0d1be44f70e768348ae6688798c84343e/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala but I couldn't find a direct link with Kafka data source...

Complete source code is here: https://github.com/boontadata/boontadata-streams/tree/ad0d0134ddb7664d359c8dca40f1d16ddd94053f

Answer 1

The issue is the following section in build.sbt:

// META-INF discarding
assemblyMergeStrategy in assembly := { 
   {
    case PathList("META-INF", xs @ _*) => MergeStrategy.discard
    case x => MergeStrategy.first
   }
}

It says that all META-INF entires should be discarded, including the "code" that makes data source aliases (e.g. kafka) work.

But the META-INF files are very important for kafka (and other aliases of streaming data sources) to work.

For kafka alias to work Spark SQL uses META-INF/services/org.apache.spark.sql.sources.DataSourceRegister with the following entry:

org.apache.spark.sql.kafka010.KafkaSourceProvider

KafkaSourceProvider is responsible to register kafka alias with the proper streaming data source, i.e. KafkaSource.

Just to check that the real code is indeed available, but the "code" that makes the alias registered is not, you could use the kafka data source by the fully-qualified name (not the alias) as follows:

spark.readStream.
  format("org.apache.spark.sql.kafka010.KafkaSourceProvider").
  load

You will see other problems due to missing options like kafka.bootstrap.servers, but...we're digressing.

A solution is to MergeStrategy.concat all META-INF/services/org.apache.spark.sql.sources.DataSourceRegister (that would create an uber-jar with all data sources, incl. the kafka data source).

case "META-INF/services/org.apache.spark.sql.sources.DataSourceRegister" => MergeStrategy.concat