...

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Machines in data center are some times grouped in racks. Racks provide isolation as each rack may be in a different physical location and has its own power source. When resources are properly replicated across racks, it provides fault tolerance in that if a rack goes down,  the remaining racks can continue to serve traffic.

In Kafka, if there are more than one replica for a partition, it would be nice to have replicas placed in as many different racks as possible so that the partition can continue to function if a rack goes down. In addition, it makes maintenance of  Kafka cluster easier as you can take down the whole rack at a time.

In AWS, racks are usually mapped to the concept of availability zones. Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

...