Notification System: Consumers and Fan Out

At peak, the sms-alerts topic receives 150 records a second, and a typical SMS provider call takes 400 ms. A consumer that makes one call at a time completes 2.5 calls a second, so the bank needs 60 calls in progress at every moment just to keep up. Allowing for the slowest normal calls, which take up to 2 seconds, it plans for twice that: 120.

With a consumer group, 120 calls at once means 120 consumers and at least 120 partitions, because each partition is read by only one consumer in a group. With a share group, 120 consumers can read a topic of 8 partitions