bug: fix kafka transport default partitioning

[lspgn]

• set default partitioner to roundrobin

[simPod]

I have tried to deploy the binary built from this PR but it seems to have no effect 🤔 Messages are still produced to only a single partition. I don't use -mapping so I suppose the key is nil.

[simPod]

I can see it is being produced with a key

[simPod]

I have tried a build where I removed this line

goflow2/transport/kafka/kafka.go

Line 233 in 3c00d97

Key: sarama.ByteEncoder(key),

and now it's distributed randomly

Unfortunately, I have no way to debug where is the key being created at the moment. I've requested tcpdump installation on the server where the sflow is being sent to so I can capture some packets, create sflow fixtures for goflow and debug it.

[lspgn]

Could you check again @simPod?

I think I found the problem: empty key had a fixed hash which didn't work with the RoundRobinPartitioner.

I'm observing it working with the expected behavior even when key is fixed. Make sure -transport.kafka.hashing=false

For reference in Bitnami Kafka docker:

Create a topic with 9 partitions

$ /opt/bitnami/kafka/bin/kafka-topics.sh --bootstrap-server localhost:9092 --create --topic flow-messages --partitions 9

Get the offsets

$ /opt/bitnami/kafka/bin/kafka-get-offsets.sh --topic flow-messages --bootstrap-server localhost:9092
flow-messages:0:1506
flow-messages:1:1506
flow-messages:2:4009
flow-messages:3:1506
flow-messages:4:1506
flow-messages:5:1506
flow-messages:6:8212
flow-messages:7:1506
flow-messages:8:1504

[simPod]

I can confirm it works without enabling -transport.kafka.hashing. This can be now closed I guess #248