With Kafka specifically the consumers of messages use standard TCP to receive messages by pulling them from Kafka. Kafka is not a push system. Consumers can come and go in and ad-hoc fashion.
https://engineering.linkedin.com/kafka/running-kafka-scale
When combined, the Kafka ecosystem at LinkedIn is sent over 800 billion messages per day which amounts to over 175 terabytes of data. Over 650 terabytes of messages are then consumed daily, which is why the ability of Kafka to handle multiple producers and multiple consumers for each topic is important. At the busiest times of day, we are receiving over 13 million messages per second, or 2.75 gigabytes of data per second. To handle all these messages, LinkedIn runs over 1100 Kafka brokers organized into more than 60 clusters.