title: Why are there no nodes under /controller znode while Kafka cluster is running?
body: <p>Output from the zookepeer client:</p>
  
  <pre><code>[zk: s1:2181(CONNECTED) 1] ls /brokers/ids
  [1, 2, 3]
  [zk: s1:2181(CONNECTED) 1] ls /controller
  []
  </code></pre>
  
  <p>There are 3 kafka brokers in the cluster, so why I can't find the controller in the /controller znode as well? </p>
  
  <p>Another question is how can I know which master election used by kafka, ZooKeeper master election or Kafka master election? Is the master election in kafka to elect the master kafka broker? So what's the leader election? Is it to elect the leader partition?</p>