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Re: Starting a seperate Java process within a Flink cluster


I am afraid that would be extremely hard what you are trying to do as in a cluster setup not all dependencies are taken from the taskmanager classpath, actually the user code classes are loaded dynamically, therefore they cannot be accessed in your new process which does not have access to those user classes.



On 02/11/2018 10:34, Jeff Zhang wrote:

The error is most likely due to classpath issue. Because classpath is different when you running flink program in IDE and run it in cluster. 

And starting another jvm process in SourceFunction doesn't seems a good approach to me, is it possible for you to do in your custom SourceFunction ?

Ly, The Anh <the.a.ly@xxxxxxxxxxxxxxxxxxx>于2018年11月2日周五 下午5:22写道:
Yes, i did. It is definitely there. I tried and made a separate Maven project to test if something was wrong with my jar. 
The resulting shaded jar of that test project was fine and the message-buffer-process was running with that test jar. 

Am 02.11.2018 04:47 schrieb Yun Tang <myasuka@xxxxxxxx>:

Since you use the message-buffer-process as a dependency and the error tells you class not found, have you ever check your application jar package whether containing the wanted MessageBufferProcess.class? If not existed, try to use assembly-maven  or shaded-maven plugin to include your classes.

Yun Tang

From: Ly, The Anh <the.a.ly@xxxxxxxxxxxxxxxxxxx>
Sent: Friday, November 2, 2018 6:33
To: user@xxxxxxxxxxxxxxxx
Subject: Starting a seperate Java process within a Flink cluster


I am currently working on my masters and I encountered a difficult problem.

Background (for context): I am trying to connect different data stream processors. Therefore i am using Flink's internal mechanisms of creating custom sinks and sources to receive from and send to different data stream processors. I am starting a separate 

process (message-buffer-process) in those custom sinks and sources to communicate and buffer data into that message-buffer-process.  My implementation is created with Maven and it could potentially be added as an dependency. 

Problem: I already tested my implementation by adding it as an dependency to a simple Flink word-count example. The test was within an IDE which works perfectly fine. But when i package that Flink work-count example and try

to run it with "./flink run " or by uploading and submitting it as a job, it tells me that my buffer-process-class could not be found:

In German: "Fehler: Hauptklasse de.tuberlin.mcc.geddsprocon.messagebuffer.MessageBufferProcess konnte nicht gefunden oder geladen werden"

Roughly translated: "Error: Main class de.tuberlin.mcc.geddsprocon.messagebuffer.MessageBufferProcess could not be found or loaded"

Code snipplets:

Example - Adding my custom sink to send data to another data stream processor:

			new DSPConnectorConfig
				.Builder("localhost", 9656)

The way i am trying to start the separate buffer-process: JavaProcessBuilder.exec(MessageBufferProcess.class, connectionString, addSentMessagesFrame);
How JavaProcessBuilder.exec looks like:
public static Process exec(Class javaClass, String connectionString, boolean addSentMessagesFrame) throws IOException, InterruptedException {
        String javaHome = System.getProperty("java.home");
        String javaBin = javaHome +
                File.separator + "bin" +
                File.separator + "java";
        String classpath = System.getProperty("java.class.path");
        String className = javaClass.getCanonicalName();

        System.out.println("Trying to build process " + classpath + " " + className);

        ProcessBuilder builder = new ProcessBuilder(
                javaBin, "-cp", classpath, className, connectionString, Boolean.toString(addSentMessagesFrame));


        Process process = builder.start();
        return process;

I also tried running that message-buffer process separately in another maven project and its packaged .jar file. That worked perfectly fine too. That is why I am assuming that my approach is not appropriate for running in Flink.
Did I miss something and starting my approach doesn't actually work within Flink's context? I hope the information I gave you is sufficient to help understanding my issue. If you need any more information feel free to message me!

Thanks for any help!

 With best regards

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