title: Flink exactly-once message processing
body: <p>I've setup a Flink 1.2 standalone cluster with 2 JobManagers and 3 TaskManagers and I'm using JMeter to load-test it by producing Kafka messages / events which are then processed. The processing job runs on a TaskManager and it usually takes ~15K events/s.<br>
  The job has set EXACTLY_ONCE checkpointing and is persisting state and checkpoints to Amazon S3.
  If I shutdown the TaskManager running the job it takes a bit, a few seconds, then the job is resumed on a different TaskManager. The job mainly logs the event ids which are consecutive integers (e.g. from  0 to 1200000).<br>
  When I check the output on the TaskManager I shut down the last count is for example 500000, then when I check the output on the resumed job on a different TaskManager it starts with ~ 400000. This means ~100K of duplicated events. This number is dependent on the speed of the test can be higher or lower.<br>
  Not sure if I'm missing something but I would expect the job to display the next consecutive number (like 500001) after resuming on the different TaskManager.<br>
  Does anyone know why this is happening / extra settings I have to configure to obtain the exactly once? </p>