A few of my jobs recently failed and showed this exception:
org.apache.flink.streaming.runtime.tasks.StreamTaskException: Cannot load user
class: org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumer09
ClassLoader info: URL ClassLoader:
file:
'/tmp/blobStore-5f023409-6af5-4de6-8ed0-e80a2eb9633e/cache/blob_d9a9fb884f3b436030afcf7b8e1bce678acceaf2'
(invalid JAR: zip file is empty)
Class not resolvable through given classloader.
at
org.apache.flink.streaming.api.graph.StreamConfig.getStreamOperator(StreamConfig.java:208)
at
org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:224)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:642)
at java.lang.Thread.run(Thread.java:745)
As you can see, Flink is storing things underneath /tmp, which is the
(undocumented) default for the blob store. As you may know, on Linux, there's
typically a program such as tmpwatch which is run periodically to clear out
data from /tmp.
Flink also uses /tmp as the default for jobmanager.web.tmpdir (and
jobmanager.web.upload.dir in 1.2).
Therefore, assuming that this is indeed the cause of the job failure/the
exception, it seems highly advisable that when you run a Flink cluster you
configure blob.storage.directory and jobmanager.web.tmpdir to a specific folder
that is not beneath /tmp. I don't know if there is any material about setting
up a production cluster, but this would definitely seem to be a necessary
configuration to specify if you want to avoid problems. Enabling High
Availability mode should also be on that list, I think.
-Shannon
