When does an Alpakka Consumer get partitions assigned?

We’re using a committableSource with a compacted topic. We are waiting for the consumer to subscribe to the topic using the RebalanceListener to “start” the application.

Note: Consumer settings are effectively default for this exercise.

  • If we set the ConsumerSettings.pollInterval to 5 seconds, it takes about 60 seconds to get the partitions assigned callback.
  • However, if we set the pollingTime to a value > 5 seconds, we never get a partition assignment call-back

Kafka indicates the consumer group was created after about 90 seconds, but has no members. The stream receives no messages.

My question is how do I get the Consumer to subscribe?