Unless you are using a custom partitioner, the DefaultPartitioner assigns them randomly so the content of the headers shouldn't make any difference.
The only explanation I can see for what you are seeing is that somehow the producer thinks there are only 2. 
Are the msgs going just to 0 and 1 or different numbers? Can you try with another topic and see if that happens too?

How are you checking where are the msg going?


On 14 December 2015 at 22:52, Guillermo Ortiz <konstt2000@gmail.com> wrote:
I'm using a an architecture as:
Logs --> SpoolDir -->MemChannel --> AvroSink  -->
AvroSource --> MemChannel --> KafkaSink.

I have a cluster with three kafka nodes and have created a topic with six partitions and replication factor one to make a POC.

I have seen that 95% of the data goes to two partitions, these two partitions are in the same kafka node. I am not creating a "key" header on my events in Flume. So, reading the documentation the key is generated randomly. The messages are logs from different sources. Is it normal this behavior?