Blocker Description
As key.serializer and value.serializer are required options when using the new producer, they should be mentioned in the documentation ( here and svn http://kafka.apache.org/documentation.html#newproducerconfigs )
Appropriate values for these options exist in javadoc and producer.java examples; however, not everyone is reading those, as is the case for anyone setting up a producer.config file for mirrormaker.
A sensible default should be suggested, such as
org.apache.kafka.common.serialization.StringSerializer
Or at least a mention of the key.serializer and value.serializer options along with a link to javadoc
Thanks