KafkaRecord 無法轉換為 [B

Question

我正在嘗試使用Python SDK for Apache Beam 和 Flink runner 處理來自 Apache Kafka 的數據流。 運行 Kafka 2.4.0 和 Flink 1.8.3 后，我按照以下步驟操作：

1) 使用 Flink 1.8 runner 編譯並運行 Beam 2.16。

git clone --single-branch --branch release-2.16.0 https://github.com/apache/beam.git beam-2.16.0
cd beam-2.16.0
nohup ./gradlew :runners:flink:1.8:job-server:runShadow -PflinkMasterUrl=localhost:8081 &

2) 運行 Python 管道。

from apache_beam import Pipeline
from apache_beam.io.external.kafka import ReadFromKafka
from apache_beam.options.pipeline_options import PipelineOptions


if __name__ == '__main__':
    with Pipeline(options=PipelineOptions([
        '--runner=FlinkRunner',
        '--flink_version=1.8',
        '--flink_master_url=localhost:8081',
        '--environment_type=LOOPBACK',
        '--streaming'
    ])) as pipeline:
        (
            pipeline
            | 'read' >> ReadFromKafka({'bootstrap.servers': 'localhost:9092'}, ['test'])  # [BEAM-3788] ???
        )
        result = pipeline.run()
        result.wait_until_finish()

3）向Kafka發布一些數據。

bin/kafka-console-producer.sh --broker-list localhost:9092 --topic test
>{"hello":"world!"}

---

Python 腳本拋出此錯誤：

[flink-runner-job-invoker] ERROR org.apache.beam.runners.fnexecution.jobsubmission.JobInvocation - Error during job invocation BeamApp-USER-somejob. org.apache.flink.client.program.ProgramInvocationException: Job failed. (JobID: xxx)
        at org.apache.flink.client.program.rest.RestClusterClient.submitJob(RestClusterClient.java:268)
        at org.apache.flink.client.program.ClusterClient.run(ClusterClient.java:483)
        at org.apache.beam.runners.flink.FlinkExecutionEnvironments$BeamFlinkRemoteStreamEnvironment.executeRemotely(FlinkExecutionEnvironments.java:360)
        at org.apache.flink.streaming.api.environment.RemoteStreamEnvironment.execute(RemoteStreamEnvironment.java:310)
        at org.apache.beam.runners.flink.FlinkStreamingPortablePipelineTranslator$StreamingTranslationContext.execute(FlinkStreamingPortablePipelineTranslator.java:173)
        at org.apache.beam.runners.flink.FlinkPipelineRunner.runPipelineWithTranslator(FlinkPipelineRunner.java:104)
        at org.apache.beam.runners.flink.FlinkPipelineRunner.run(FlinkPipelineRunner.java:80)
        at org.apache.beam.runners.fnexecution.jobsubmission.JobInvocation.runPipeline(JobInvocation.java:78)
        at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.util.concurrent.TrustedListenableFutureTask$TrustedFutureInterruptibleTask.runInterruptibly(TrustedListenableFutureTask.java:125)
        at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.util.concurrent.InterruptibleTask.run(InterruptibleTask.java:57)
        at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.util.concurrent.TrustedListenableFutureTask.run(TrustedListenableFutureTask.java:78)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
        at org.apache.flink.runtime.jobmaster.JobResult.toJobExecutionResult(JobResult.java:146)
        at org.apache.flink.client.program.rest.RestClusterClient.submitJob(RestClusterClient.java:265)
        ... 13 more
Caused by: java.lang.ClassCastException: org.apache.beam.sdk.io.kafka.KafkaRecord cannot be cast to [B
        at org.apache.beam.sdk.coders.ByteArrayCoder.encode(ByteArrayCoder.java:41)
        at org.apache.beam.sdk.coders.LengthPrefixCoder.encode(LengthPrefixCoder.java:56)
        at org.apache.beam.sdk.values.ValueWithRecordId$ValueWithRecordIdCoder.encode(ValueWithRecordId.java:105)
        at org.apache.beam.sdk.values.ValueWithRecordId$ValueWithRecordIdCoder.encode(ValueWithRecordId.java:81)
        at org.apache.beam.sdk.util.WindowedValue$FullWindowedValueCoder.encode(WindowedValue.java:578)
        at org.apache.beam.sdk.util.WindowedValue$FullWindowedValueCoder.encode(WindowedValue.java:529)
        at org.apache.beam.sdk.util.CoderUtils.encodeToSafeStream(CoderUtils.java:82)
        at org.apache.beam.sdk.util.CoderUtils.encodeToByteArray(CoderUtils.java:66)
        at org.apache.beam.sdk.util.CoderUtils.encodeToByteArray(CoderUtils.java:51)
        at org.apache.beam.sdk.util.CoderUtils.clone(CoderUtils.java:141)
        at org.apache.beam.runners.flink.translation.types.CoderTypeSerializer.copy(CoderTypeSerializer.java:67)
        at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:577)
        at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:554)
        at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:534)
        at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:718)
        at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:696)
        at org.apache.flink.streaming.api.operators.StreamSourceContexts$ManualWatermarkContext.processAndCollect(StreamSourceContexts.java:305)
        at org.apache.flink.streaming.api.operators.StreamSourceContexts$WatermarkContext.collect(StreamSourceContexts.java:394) at org.apache.beam.runners.flink.translation.wrappers.streaming.io.UnboundedSourceWrapper.emitElement(UnboundedSourceWrapper.java:341)
        at org.apache.beam.runners.flink.translation.wrappers.streaming.io.UnboundedSourceWrapper.run(UnboundedSourceWrapper.java:283)
        at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:93)
        at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:57)
        at org.apache.flink.streaming.runtime.tasks.SourceStreamTask.run(SourceStreamTask.java:97)
        at org.apache.flink.streaming.runtime.tasks.StoppableSourceStreamTask.run(StoppableSourceStreamTask.java:45)
        at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:302)
        at org.apache.flink.runtime.taskmanager.Task.run(Task.java:711)
        ... 1 more
ERROR:root:java.lang.ClassCastException: org.apache.beam.sdk.io.kafka.KafkaRecord cannot be cast to [B
[flink-runner-job-invoker] INFO org.apache.beam.runners.fnexecution.artifact.BeamFileSystemArtifactRetrievalService - Manifest at/tmp/artifacts0k1mnin0/somejob/MANIFEST has 0 artifact locations
[flink-runner-job-invoker] INFO org.apache.beam.runners.fnexecution.artifact.BeamFileSystemArtifactStagingService - Removed dir /tmp/artifacts0k1mnin0/job_somejob/
Traceback (most recent call last):
  File "main.py", line 40, in <module>
    run()
  File "main.py", line 37, in run
    result.wait_until_finish()
  File "/home/USER/beam/lib/python3.5/site-packages/apache_beam/runners/portability/portable_runner.py", line 439, in wait_until_finish self._job_id, self._state, self._last_error_message()))
RuntimeError: Pipeline BeamApp-USER-somejob failed in state FAILED: java.lang.ClassCastException: org.apache.beam.sdk.io.kafka.KafkaRecord cannot be cast to [B

我嘗試了 Kafka 中可用的其他反序列化器，但它們不起作用： Couldn't infer Coder from class org.apache.kafka.common.serialization.StringDeserializer 。 此錯誤源於這段代碼。

難道我做錯了什么？

Answer 1

免責聲明：這是我第一次接觸 Apache Beam 項目。

根據這個JIRA ，似乎 Kafka 消費者支持在 Beam 中（至少在 Python 接口中）是相當新鮮的。 顯然， FlinkRunner結合這個新 API似乎仍然存在問題。 即使你的代碼在技術上是正確的，它也不會在 Flink 上正確運行。 有一個可用補丁對我來說更像是一個快速修復而不是最終解決方案。 它需要重新編譯，因此我不建議在生產中使用它。 如果您剛剛開始使用技術並且不想被阻止，那么請隨意嘗試。