Kafkasender

[rifatdover]

This PR add functionality to logstash-gelf to log Kafka as Producer

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[rifatdover]

Please do not merge. I think there is a problem similar to danielwegener/logback-kafka-appender#44

[rifatdover]

Well the problem emerges with SL4J. KafkaProducer request a Logger with package name org.apache.kafka or javax.management while it is sending. And creates a deadlock.

Also it is possible working with different appenders for them:

 <root level="ALL">
        <appender-ref ref="gelfKafka" />
    </root>
    <logger name="org.apache.kafka" level="ALL" additivity="false">
        <appender-ref ref="gelfUdp" />
    </logger>
    <logger name="javax.management" level="ALL" additivity="false">
        <appender-ref ref="gelfUdp" />
    </logger>

Well even if I don't like that it will be ok for everyone. Because what I believe Kafka would be used for a failover scenerio of Graylog down in an application architecture. And when graylog is down nobody will care about these logs?

Adding it in documentation limitations section would do the job. What do you think? @mp911de

[mp911de]

Thanks a lot for your pull request. I added a few review comments. I see two major issues here:

1. We shouldn't add another config system to configure Kafka but rather stick to how we configure e.g. the Redis sender and move all extended properties into the URL. We also should not extend appender config/properties for technology-specific extensions as this requires changes to our public API and causes confusion where to configure settings.
2. Logger deadlock: The mentioned limitation/workaround is inevitable if we integrate with third-party dependencies that require a logger – we're already in a logger component and so (re)using a logger can easily lead to problems, that's why we introduced ErrorReporter. For Kafka, the only thing we can do is providing proper documentation and a warning about the issue so people do not discover this shortcoming in production.

Care to have a look and address the review comments?

[mp911de]

Awesome work! Thanks a lot. Can you do the two following things to make merging a bit easier:

• Squash your commits to a single commit
• Reformat the newly introduced classes using our Eclipse formatter settings. Some files contain double-linebreaks and this makes it easier to have consistent formatting.

[rifatdover]

All done 👍

[mp911de]

Thanks a lot. That's merged and polished now.