Github user mikaelstaldal commented on the issue:
https://github.com/apache/logging-log4j2/pull/112
@flowcont I think it would make more sense to have the value for the key as
an attribute on the Kafka appender element, and not as a nested property, since
the nested properties are passed directly to the [Kafka client
library](http://kafka.apache.org/documentation.html#producerconfigs).
So you can specify it like this:
```
<Appenders>
<Kafka name="Kafka" topic="log-test" key="myKey">
<PatternLayout pattern="%date %message"/>
<Property name="bootstrap.servers">localhost:9092</Property>
</Kafka>
</Appenders>
```
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