COORDINATOR_NOT_AVAILABLE with single node cluster

When using single node cluster, consumer groups are unable to retrieve messages from a topic because, by default, we have "offsets.topic.replication.factor = 3" and so "__consumer_offsets" internal topic can't be created.

To make it work you need to set the following values at the broker level:

• offsets.topic.replication.factor = 1
• transaction.state.log.replication.factor = 1
• transaction.state.log.min.isr = 1

When this happens, the application shows error=COORDINATOR_NOT_AVAILABLE only at DEBUG level. The overall application behavior is much like when there is no data. We should at least add some WARN level logging if the RF for the internal topics is < the Kafka replicas.