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✓you are having concurrency as 2 , which means 2 containers will be created to your listener.
✓As you are having 2 partitions in topic , messages from both the partitions will be consumed and processed parallelly.
✓When you spin up one more instance with same group name , the first thing that will happen is Group Rebalance . ✓Despite this event , as at any point of time only one consumer from a specific consumer group can be there for a partition , In the end , only 2 containers will be listening to messages and other 2 containers just remain idle.
✓In order to achieve more scalability , we need to add more number of partitions to the topic there by we can have more number of active listener containers
