Idempotent Producer

 1. Here's the problem: the Producer can introduce duplicate messages in Kakka due to network errors

- In Kafka >= 0.11, you can define a "idempotent producer" which won't introduce duplicates on network error

- Idempotent producers are great to guarantee a stable and safe pipeline!

- They come with:

    - retries = Integer.MAX_VALUE(2^31-1 = 2147483647)

    - max.in.flight.requests = I (Kafka >= 0.11 & < 1.1) or

    - max.in.flight.requests = 5 (Kafka >= 1.1 - higher performance)

    - acks = all

- Just set:

    - producerProps.put("enable.idempotence", true);