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In AWS, racks are usually mapped to the concept of availability zones. 

Public Interfaces

One optional parameter rackInfo will be passed to AdminUtils.assignReplicasToBrokers:

/**
 * @param rackInfo Map from broker ID to its rack (zone). If empty, no rack aware
 *                 assignment will be used.
 */
def assignReplicasToBrokers(brokerList: Seq[Int],
                            nPartitions: Int,
                            replicationFactor: Int,
                            fixedStartIndex: Int = -1,
                            startPartitionId: Int = -1,
                            rackInfo: Map[Int, String] = Map()) 

The RackLocator interface will be used to return rack information for brokers at runtime and for command line. It is defined as:

/**
 * Interface that defines API to get broker to rack mapping. This is used by
 * rack aware replica assignment. The implementation class can be passed as
 * rack.locator.class property at server start up or -rack-locator-class command\
 * line argument for TopicCommand.
 *
 * @param zkClient ZkClient for the cluster that can be used to retrieve information
 *                 from ZooKeeper
 * @param props Properties used by implementation.
 */
abstract class RackLocator(val zkClient: ZkClient, val props: Properties) {
  def getRackInfo(): Map[Int, String]
}

zkClient is passed into the interface in case the implementation stores the rack information in the same ZooKeeper path as the Kafka cluster or needs to access cluster meta data information from the ZooKeeper. Implementation can use the additional properties passed into the interface to initialize and access the storage where the rack information is stored. The single method getRackInfo() returns a map that maps a broker ID to the rack ID represented as a string.

The following optional properties can be used when Kafka broker starts:

• rack.locator.class: The implementation class 

Proposed Changes

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