by default the Kafka client APIs log a lot on INFO. On IRC Polina and Dimitra were mentioning that.
Here is a snippet for the "standalone.xml", to be inserted in the logging subsystem:
<logger category="org.apache.kafka.streams.processor">
<level name="WARN"/>
</logger>
<logger category="org.apache.kafka.clients.producer.ProducerConfig">
<level name="WARN"/>
</logger>
<logger category="org.apache.kafka.clients.consumer.ConsumerConfig">
<level name="WARN"/>
</logger>
<logger category="org.apache.kafka.streams.StreamsConfig">
<level name="WARN"/>
</logger>