If there are 100 consumers in one consumer group with 10 partitions — how will it work?

In Kafka, the number of consumers in a consumer group and the number of partitions in a topic are directly related to how messages are distributed.

If you have 10 partitions and 100 consumers in one group, then:

• Each partition can be assigned to only one consumer in the group.
• Since there are fewer partitions than consumers, only 10 consumers will be active and receive data.
• The remaining 90 consumers will be idle, as they will not be assigned any partitions.

In conclusion: the maximum number of active consumers in a group equals the number of partitions. Excess consumers do not increase parallelism but only create unused instances.