不多说，直接上干货！
一切来源于官网
http://kafka.apache.org/documentation/
Distribution
分布式(Distribution)
The partitions of the log are distributed over the servers in the Kafka cluster with each server handling data and requests for a share of the partitions. Each partition is replicated across a configurable number of servers for fault tolerance.
Log的分区被分布到集群中的多个服务器上。每个服务器处理它分到的分区。 根据配置每个分区还可以复制到其它服务器作为备份容错。
Each partition has one server which acts as the "leader" and zero or more servers which act as "followers". The leader handles all read and write requests for the partition while the followers passively replicate the leader. If the leader fails, one of the followers will automatically become the new leader. Each server acts as a leader for some of its partitions and a follower for others so load is well balanced within the cluster.
每个分区有一个leader，零或多个follower。Leader处理此分区的所有的读写请求，而follower被动的复制数据。
如果leader宕机，其它的一个follower会被推举为新的leader。
一台服务器可能同时是一个分区的leader，另一个分区的follower。
这样可以平衡负载，避免所有的请求都只让一台或者某几台服务器处理。