Minor Description
If we describe a non-existing group before the offset topic is created, like the following:
bin/kafka-consumer-groups.sh --bootstrap-server localhost:9092 --new-consumer --describe --group gggg
We get the following error:
Error while executing consumer group command The group coordinator is not available.
org.apache.kafka.common.errors.GroupCoordinatorNotAvailableException: The group coordinator is not available.
The exception is thrown in the `adminClient.describeConsumerGroup` call. We can't interpret this exception as meaning that the group doesn't exist because it could also be thrown f all replicas for a offset topic partition are down (as explained by Jun).
Jun also suggested that we should distinguish if a coordinator is not available from the case where a coordinator doesn't exist.
