Kafka Streams is a library for building streaming applications, specifically applications that transform input Kafka topics into output Kafka topics

Log compaction retains at least the last known value for each record key for a single topic partition. All compacted log offsets remain valid, even if record at offset has been compacted away as a consumer will get the next highest offset.

Message with no keys will be stored with round-robin strategy among partitions.

Callback is invoked when a broker response is received.

subscribe() and assign() cannot be called by the same consumer, subscribe() is used to leverage the consumer group mechanism, while assign() is used to manually control partition assignment and reads assignment

Consumers do not directly write to the __consumer_offsets topic, they instead interact with a broker that has been elected to manage that topic, which is the Group Coordinator broker

Your Zookeeper cluster needs to have an odd number of servers, and must maintain a majority of servers up to be able to vote. Therefore, a 2N+1 zookeeper cluster can survive to N zookeeper being down, so here the right answer is N=2, 2*N+1=5

Example: kafka-console-consumer --bootstrap-server 127.0.0.1:9092 --topic test --from-beginning

This will allow consumers to wait and receive more bytes in each fetch request.

ACLs take "Host" as a parameter, which represents an IP. It can be * (all IP), or a specific IP. Here, it's a specific IP as moving a producer to a different machine breaks the consumer, so the ACL needs to be updated