These are properties that are available within producer.properties when executing:
./bin/kafka-console-producer.sh --producer.config ./config/producer.properties
2018-11-20 23:25:16.445 WARN 7204 — [ad | producer-1] o.a.k.common.network.SslTransportLayer : Failed to send SSL Close message
java.io.IOException: Broken pipe
at sun.nio.ch.FileDispatcherImpl.write0(Native Method) ~[na:1.8.0_162]
at sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:47) ~[na:1.8.0_162]
at sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:93) ~[na:1.8.0_162]
at sun.nio.ch.IOUtil.write(IOUtil.java:65) ~[na:1.8.0_162]
at sun.nio.ch.SocketChannelImpl.write(SocketChannelImpl.java:471) ~[na:1.8.0_162]
at org.apache.kafka.common.network.SslTransportLayer.flush(SslTransportLayer.java:213) ~[kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.SslTransportLayer.close(SslTransportLayer.java:176) ~[kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.utils.Utils.closeAll(Utils.java:703) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.KafkaChannel.close(KafkaChannel.java:61) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.Selector.doClose(Selector.java:741) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.Selector.close(Selector.java:729) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:522) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.common.network.Selector.poll(Selector.java:412) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:460) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:216) [kafka-clients-1.0.2.jar:na]
at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:163) [kafka-clients-1.0.2.jar:na]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_162]
Axon just passes the configuration provided in the ProducerFactory straight to Kafka. So whatever properties you need to define, are Kafka-specific. According to the Javadoc on org.apache.kafka.clients.producer.KafkaProducer#KafkaProducer(java.util.Map<java.lang.String,java.lang.Object>), you should be able to find all properties here: http://kafka.apache.org/documentation.html#producerconfigs