可以发出什么命令来检查ZooKeeper服务器是Leader还是Follower？

Question

已创建由三个 ZooKeeper 服务器组成的 ZooKeeper Quorum。

在zoo.cfg所有三个ZooKeeper的服务器看起来位于如下：

maxClientCnxns=50
# The number of milliseconds of each tick
tickTime=2000
# The number of ticks that the initial
# synchronization phase can take
initLimit=10
# The number of ticks that can pass between
# sending a request and getting an acknowledgement
syncLimit=5
# the directory where the snapshot is stored.
dataDir=/var/lib/zookeeper
# the port at which the clients will connect
clientPort=2181

server.1=<ip-address-1>:2888:3888
server.2=<ip-address-2>:2888:3888
server.3=<ip-address-3>:2888:3888

---

分析

很明显，三个 ZooKeeper 服务器之一将成为 ，Leader而其他服务器将成为Followers。如果LeaderZooKeeper 服务器已经关闭，Leader选举将重新开始。目的是检查另一个 ZooKeeper 服务器是否会成为服务器已关闭Leader的Leader服务器。

Answer 1

可以使用包中nc包含的命令检查 ZooKeeper 服务器是领导者还是追随者netcat：

echo stat | nc localhost 2181 | grep Mode
echo srvr | nc localhost 2181 | grep Mode #(From 3.3.0 onwards)

如果 ZooKeeper 服务器是领导者，则该命令将返回：Mode: leader否则：Mode: follower

Answer 2

或者，可以使用以下方法：

bin/zkServer.sh status

它将在输出中打印模式：

ZooKeeper JMX enabled by default
Using config: /home/kafka/zookeeper/bin/../conf/zoo.cfg
Mode: follower