title: kafka: keep track of producer offset
body: <p>I'm using Apache Kafka <em>(no confluent)</em> and have a simple Kafka producer that pulls from a rest API, sends data to Kafka and shuts down.
  I had this for testing while I was developing a consumer.</p>
  
  <p>In the consumer I can keep track of the offset, but I don't seem to be able to set a custom offset in my producer.</p>
  
  <p>In my rest calls I would need to keep track of a date so that I don't pull the same data all the time. Am I forced to store that "last timestamp" myself or am I missing something?</p>