[FLINK-17819][yarn] Fix error msg for yarn deployments when hadoop not in classpath

[kl0u]

What is the purpose of the change

This PR simply changes the error message presented to the user when he/she is trying to submit to Yarn but hadoop is not in the classpath. The new message will be:

No Executor found. Please make sure to have hadoop in your classpath. For more information on how to do so refer to the "Deployment & Operations" section of the official Apache Flink documentation.

Brief change log

The changes are:

1. a FallbackYarnSessionCli that will be loaded by the CliFrontend in case there is a loading error when the frontend tries to load the actual FlinkYarnSessionCli. This cli will simply throw an exception with the above message when it detects that the FlinkYarnSessionCli would be used but it failed to be loaded (the isActive method).
2. change of the error message in the YarnJobClusterExecutorFactory and the YarnSessionClusterExecutorFactory when the executor cannot be instantiated. This is to cover for the case where the user tries to access a Yarn cluster through the ExecutorCLI.

Verifying this change

Was verified manually and also added the FallbackYarnSessionCliTest.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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[aljoscha]

Suggested change

	"hadoop in your classpath. For more information refer to the \"Deployment & Operations\" section " +
	"Hadoop in your classpath. For more information refer to the \"Deployment & Operations\" section " +

maybe also say sth aboutHADOOP_CLASSPATH here.

[kl0u]

Actually this is wrong now because we load the FallbackYarnSessionCLI so if we reach here, it is not simply because of the classpath.

[aljoscha]

Suggested change

	"hadoop in your classpath. For more information refer to the " +
	"Hadoop in your classpath. For more information refer to the " +

same as above, also mention HADOOP_CLASSPATH

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CI report:

• ea59a14 Azure: SUCCESS

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[kl0u]

Thanks for the comments @aljoscha. I updated the PR accordingly. Let me know what you think.

[wangyang0918]

Thanks a lot for this PR. It will help our users a lot when the hadoop is not correctly configured.

For yarn-session.sh, it has the same problem. But the exception is easier to understand. Maybe it is already enough.

wangyang-pc:build-target danrtsey.wy$ ./bin/yarn-session.sh
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/yarn/exceptions/YarnException
	at java.lang.Class.getDeclaredMethods0(Native Method)
	at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
	at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
	at java.lang.Class.getMethod0(Class.java:3018)
	at java.lang.Class.getMethod(Class.java:1784)
	at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
	at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.yarn.exceptions.YarnException
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 7 more

[wangyang0918]

So we are intentional to ignore the Yarn properties file here. Right?

[kl0u]

Yes, the reason is that:

1. we would have to copy more code
2. I would assume that if we have the properties (hidden) file, it means that we created the Yarn cluster using the session CLI, so we already have hadoop in the classpath.

(In fact the solution here is already fragile, as whoever touches the isActive() should know to keep both methods in sync)

Do you agree @wangyang0918 ?

[wangyang0918]

Yeah, i agree with you that we do not need to add the logics for Yarn magic properties file here.

[wangyang0918]

The changes looks really good to me. +1 for merging.