ZooKeeper是一个分布式开源框架，提供了协调分布式应用的基本服务，它向外部应用暴露一组通用服务——分布式同步（Distributed Synchronization）、命名服务（Naming Service）、集群维护（Group Maintenance）等，简化分布式应用协调及其管理的难度，提供高性能的分布式服务。ZooKeeper本身可以以Standalone模式安装运行，不过它的长处在于通过分布式ZooKeeper集群（一个Leader，多个Follower），基于一定的策略来保证ZooKeeper集群的稳定性和可用性，从而实现分布式应用的可靠性。 有关ZooKeeper的介绍，网上很多，也可以参考文章后面，我整理的一些相关链接。 ZooKeeper的安装配置还算比较容易的，下面，我们简单说明一下ZooKeeper的配置。
ZooKeeper Standalone模式
从Apache网站上（zookeeper.apache.org）下载ZooKeeper软件包，我选择了3.3.4版本的（zookeeper-3.3.4.tar.gz），在一台Linux机器上安装非常容易，只需要解压缩后，简单配置一下即可以启动ZooKeeper服务器进程。 将zookeeper-3.3.4/conf目录下面的 zoo_sample.cfg修改为zoo.cfg，配置文件内容如下所示：
tickTime=2000
dataDir=/home/hadoop/storage/zookeeper
clientPort=2181
initLimit=5
syncLimit=2
上面各个配置参数的含义也非常简单，引用如下所示：
tickTime —— the basic time unit in milliseconds used by ZooKeeper. It is used to do heartbeats and the minimum session timeout will be twice the tickTime. dataDir —— the location to store the in-memory database snapshots and, unless specified otherwise, the transaction log of updates to the database. clientPort —— the port to listen for client connections
下面启动ZooKeeper服务器进程：
cd zookeeper-3.3.4/
bin/zkServer.sh start
通过jps命令可以查看ZooKeeper服务器进程，名称为QuorumPeerMain。
在客户端连接ZooKeeper服务器，执行如下命令：
bin/zkCli.sh -server dynamic:2181
客户端连接信息如下所示：
shirdrn@master:~/installation/zookeeper-3.3.4$ bin/zkCli.sh -server dynamic:2181
Connecting to dynamic:2181
2013-10-28 21:30:06,178 - INFO [main:Environment@97] - Client environment:zookeeper.version=3.3.3-1203054, built on 11/17/2011 05:47 GMT
2013-10-28 21:30:06,188 - INFO [main:Environment@97] - Client environment:host.name=master
2013-10-28 21:30:06,191 - INFO [main:Environment@97] - Client environment:java.version=1.6.0_30
2013-10-28 21:30:06,194 - INFO [main:Environment@97] - Client environment:java.vendor=Sun Microsystems Inc.
2013-10-28 21:30:06,200 - INFO [main:Environment@97] - Client environment:java.home=/home/hadoop/installation/jdk1.6.0_30/jre
2013-10-28 21:30:06,203 - INFO [main:Environment@97] - Client environment:java.class.path=/home/hadoop/installation/zookeeper-3.3.4/bin/../build/classes:/home/hadoop/installation/zookeeper-3.3.4/bin/../build/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../zookeeper-3.3.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/log4j-1.2.15.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/jline-0.9.94.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-lang-2.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-collections-3.2.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-cli-1.1.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-tasks-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-core-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../src/java/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../conf:/home/hadoop/installation/jdk1.6.0_30/lib/*.jar:/home/hadoop/installation/jdk1.6.0_30/jre/lib/*.jar
2013-10-28 21:30:06,206 - INFO [main:Environment@97] - Client environment:java.library.path=/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib
2013-10-28 21:30:06,213 - INFO [main:Environment@97] - Client environment:java.io.tmpdir=/tmp
2013-10-28 21:30:06,216 - INFO [main:Environment@97] - Client environment:java.compiler=<NA>
2013-10-28 21:30:06,235 - INFO [main:Environment@97] - Client environment:os.name=Linux
2013-10-28 21:30:06,244 - INFO [main:Environment@97] - Client environment:os.arch=i386
2013-10-28 21:30:06,246 - INFO [main:Environment@97] - Client environment:os.version=3.0.0-14-generic
2013-10-28 21:30:06,251 - INFO [main:Environment@97] - Client environment:user.name=hadoop
2013-10-28 21:30:06,254 - INFO [main:Environment@97] - Client environment:user.home=/home/hadoop
2013-10-28 21:30:06,255 - INFO [main:Environment@97] - Client environment:user.dir=/home/hadoop/installation/zookeeper-3.3.4
2013-10-28 21:30:06,264 - INFO [main:ZooKeeper@379] - Initiating client connection, connectString=dynamic:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@bf32c
2013-10-28 21:30:06,339 - INFO [main-SendThread():ClientCnxn$SendThread@1061] - Opening socket connection to server dynamic/192.168.0.107:2181
Welcome to ZooKeeper!
2013-10-28 21:30:06,397 - INFO [main-SendThread(dynamic:2181):ClientCnxn$SendThread@950] - Socket connection established to dynamic/192.168.0.107:2181, initiating session
JLine support is enabled
2013-10-28 21:30:06,492 - INFO [main-SendThread(dynamic:2181):ClientCnxn$SendThread@739] - Session establishment complete on server dynamic/192.168.0.107:2181, sessionid = 0x134b9b714f9000c, negotiated timeout = 30000 WATCHER:: WatchedEvent state:SyncConnected type:None path:null
[zk: dynamic:2181(CONNECTED) 0]
接着，可以使用help查看Zookeeper客户端可以使用的基本操作命令。
ZooKeeper Distributed模式
ZooKeeper分布式模式安装（ZooKeeper集群）也比较容易，这里说明一下基本要点。 首先要明确的是，ZooKeeper集群是一个独立的分布式协调服务集群，“独立”的含义就是说，如果想使用ZooKeeper实现分布式应用的协调与管理，简化协调与管理，任何分布式应用都可以使用，这就要归功于Zookeeper的数据模型（Data Model）和层次命名空间（Hierarchical Namespace）结构，详细可以参考http://zookeeper.apache.org/doc/trunk/zookeeperOver.html。在设计你的分布式应用协调服务时，首要的就是考虑如何组织层次命名空间。 下面说明分布式模式的安装配置，过程如下所示：
第一步：主机名称到IP地址映射配置 ZooKeeper集群中具有两个关键的角色：Leader和Follower。集群中所有的结点作为一个整体对分布式应用提供服务，集群中每个结点之间都互相连接，所以，在配置的ZooKeeper集群的时候，每一个结点的host到IP地址的映射都要配置上集群中其它结点的映射信息。
例如，我的ZooKeeper集群中每个结点的配置，以zk-01为例，/etc/hosts内容如下所示:
192.168.0.179 zk-01
192.168.0.178 zk-02
192.168.0.177 zk-03
ZooKeeper采用一种称为Leader election的选举算法。在整个集群运行过程中，只有一个Leader，其他的都是Follower，如果ZooKeeper集群在运行过程中Leader出了问题，系统会采用该算法重新选出一个Leader。因此，各个结点之间要能够保证互相连接，必须配置上述映射。
ZooKeeper集群启动的时候，会首先选出一个Leader，在Leader election过程中，某一个满足选举算的结点就能成为Leader。整个集群的架构可以参考http://zookeeper.apache.org/doc/trunk/zookeeperOver.html#sc_designGoals。
第二步：修改ZooKeeper配置文件
在其中一台机器（zk-01）上，解压缩zookeeper-3.3.4.tar.gz，修改配置文件conf/zoo.cfg，内容如下所示：
tickTime=2000
dataDir=/home/hadoop/storage/zookeeper
clientPort=2181
initLimit=5
syncLimit=2
server.1=zk-01:2888:3888
server.2=zk-02:2888:3888
server.3=zk-03:2888:3888
上述配置内容说明，可以参考http://zookeeper.apache.org/doc/trunk/zookeeperStarted.html#sc_RunningReplicatedZooKeeper。
第三步：远程复制分发安装文件
上面已经在一台机器zk-01上配置完成ZooKeeper，现在可以将该配置好的安装文件远程拷贝到集群中的各个结点对应的目录下：
cd /home/hadoop/installation/
scp -r zookeeper-3.3.4/ shirdrn@zk-02:/home/hadoop/installation/
scp -r zookeeper-3.3.4/ shirdrn@zk-03:/home/hadoop/installation/
第四步：设置myid
在我们配置的dataDir指定的目录下面，创建一个myid文件，里面内容为一个数字，用来标识当前主机，conf/zoo.cfg文件中配置的server.X中X为什么数字，则myid文件中就输入这个数字，例如：
shirdrn@zk-01:~/installation/zookeeper-3.3.4$ echo "1" > /home/hadoop/storage/zookeeper/myid
shirdrn@zk-02:~/installation/zookeeper-3.3.4$ echo "2" > /home/hadoop/storage/zookeeper/myid
shirdrn@zk-03:~/installation/zookeeper-3.3.4$ echo "3" > /home/hadoop/storage/zookeeper/myid
按照上述进行配置即可。
第五步：启动ZooKeeper集群
在ZooKeeper集群的每个结点上，执行启动ZooKeeper服务的脚本，如下所示：
shirdrn@zk-01:~/installation/zookeeper-3.3.4$ bin/zkServer.sh start
shirdrn@zk-02:~/installation/zookeeper-3.3.4$ bin/zkServer.sh start
shirdrn@zk-03:~/installation/zookeeper-3.3.4$ bin/zkServer.sh start
以结点zk-01为例，日志如下所示：
shirdrn@zk-01:~/installation/zookeeper-3.3.4$ tail -500f zookeeper.out
2013-10-28 06:51:19,117 - INFO [main:QuorumPeerConfig@90] - Reading configuration from: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg
2013-10-28 06:51:19,133 - INFO [main:QuorumPeerConfig@310] - Defaulting to majority quorums
2013-10-28 06:51:19,167 - INFO [main:QuorumPeerMain@119] - Starting quorum peer
2013-10-28 06:51:19,227 - INFO [main:NIOServerCnxn$Factory@143] - binding to port 0.0.0.0/0.0.0.0:2181
2013-10-28 06:51:19,277 - INFO [main:QuorumPeer@819] - tickTime set to 2000
2013-10-28 06:51:19,278 - INFO [main:QuorumPeer@830] - minSessionTimeout set to -1
2013-10-28 06:51:19,279 - INFO [main:QuorumPeer@841] - maxSessionTimeout set to -1
2013-10-28 06:51:19,281 - INFO [main:QuorumPeer@856] - initLimit set to 5
2013-10-28 06:51:19,347 - INFO [Thread-1:QuorumCnxManager$Listener@473] - My election bind port: 3888
2013-10-28 06:51:19,393 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumPeer@621] - LOOKING
2013-10-28 06:51:19,396 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@663] - New election. My id = 1, Proposed zxid = 0
2013-10-28 06:51:19,400 - INFO [WorkerReceiver Thread:FastLeaderElection@496] - Notification: 1 (n.leader), 0 (n.zxid), 1 (n.round), LOOKING (n.state), 1 (n.sid), LOOKING (my state)
2013-10-28 06:51:19,416 - WARN [WorkerSender Thread:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/192.168.0.178:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.toSend(QuorumCnxManager.java:340)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.process(FastLeaderElection.java:360)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.run(FastLeaderElection.java:333)
at java.lang.Thread.run(Thread.java:662)
2013-10-28 06:51:19,420 - WARN [WorkerSender Thread:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.toSend(QuorumCnxManager.java:340)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.process(FastLeaderElection.java:360)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.run(FastLeaderElection.java:333)
at java.lang.Thread.run(Thread.java:662)
2013-10-28 06:51:19,612 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/192.168.0.178:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:19,615 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:19,616 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 400
2013-10-28 06:51:20,019 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/192.168.0.178:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:20,021 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:20,022 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 800
2013-10-28 06:51:20,825 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/192.168.0.178:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:20,827 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:20,828 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 1600
2013-10-28 06:51:22,435 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/192.168.0.178:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:22,439 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:51:22,441 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 3200
2013-10-28 06:51:22,945 - INFO [WorkerReceiver Thread:FastLeaderElection@496] - Notification: 2 (n.leader), 0 (n.zxid), 1 (n.round), LOOKING (n.state), 2 (n.sid), LOOKING (my state)
2013-10-28 06:51:22,946 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@721] - Updating proposal
2013-10-28 06:51:22,949 - WARN [WorkerSender Thread:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/192.168.0.177:3888
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:567)
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.toSend(QuorumCnxManager.java:340)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.process(FastLeaderElection.java:360)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.run(FastLeaderElection.java:333)
at java.lang.Thread.run(Thread.java:662)
2013-10-28 06:51:22,951 - INFO [WorkerReceiver Thread:FastLeaderElection@496] - Notification: 2 (n.leader), 0 (n.zxid), 1 (n.round), LOOKING (n.state), 1 (n.sid), LOOKING (my state)
2013-10-28 06:51:23,156 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumPeer@643] - FOLLOWING
2013-10-28 06:51:23,170 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Learner@80] - TCP NoDelay set to: true
2013-10-28 06:51:23,206 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:zookeeper.version=3.3.3-1203054, built on 11/17/2011 05:47 GMT
2013-10-28 06:51:23,207 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:host.name=zk-01
2013-10-28 06:51:23,207 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.version=1.6.0_30
2013-10-28 06:51:23,208 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.vendor=Sun Microsystems Inc.
2013-10-28 06:51:23,208 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.home=/home/hadoop/installation/jdk1.6.0_30/jre
2013-10-28 06:51:23,209 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.class.path=/home/hadoop/installation/zookeeper-3.3.4/bin/../build/classes:/home/hadoop/installation/zookeeper-3.3.4/bin/../build/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../zookeeper-3.3.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/log4j-1.2.15.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/jline-0.9.94.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-lang-2.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-collections-3.2.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-cli-1.1.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-tasks-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-core-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../src/java/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../conf:/home/hadoop/installation/jdk1.6.0_30/lib/*.jar:/home/hadoop/installation/jdk1.6.0_30/jre/lib/*.jar
2013-10-28 06:51:23,210 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.library.path=/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib
2013-10-28 06:51:23,210 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.io.tmpdir=/tmp
2013-10-28 06:51:23,212 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:java.compiler=<NA>
2013-10-28 06:51:23,212 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:os.name=Linux
2013-10-28 06:51:23,212 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:os.arch=i386
2013-10-28 06:51:23,213 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:os.version=3.0.0-14-generic
2013-10-28 06:51:23,213 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:user.name=hadoop
2013-10-28 06:51:23,214 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:user.home=/home/hadoop
2013-10-28 06:51:23,214 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Environment@97] - Server environment:user.dir=/home/hadoop/installation/zookeeper-3.3.4
2013-10-28 06:51:23,223 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:ZooKeeperServer@151] - Created server with tickTime 2000 minSessionTimeout 4000 maxSessionTimeout 40000 datadir /home/hadoop/storage/zookeeper/version-2 snapdir /home/hadoop/storage/zookeeper/version-2
2013-10-28 06:51:23,339 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Learner@294] - Getting a snapshot from leader
2013-10-28 06:51:23,358 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:Learner@325] - Setting leader epoch 1
2013-10-28 06:51:23,358 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FileTxnSnapLog@254] - Snapshotting: 0
2013-10-28 06:51:25,511 - INFO [WorkerReceiver Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 0 (n.zxid), 1 (n.round), LOOKING (n.state), 3 (n.sid), FOLLOWING (my state)
2013-10-28 06:51:42,584 - INFO [WorkerReceiver Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 0 (n.zxid), 2 (n.round), LOOKING (n.state), 3 (n.sid), FOLLOWING (my state)
我启动的顺序是zk-01>zk-02>zk-03，由于ZooKeeper集群启动的时候，每个结点都试图去连接集群中的其它结点，先启动的肯定连不上后面还没启动的，所以上面日志前面部分的异常是可以忽略的。通过后面部分可以看到，集群在选出一个Leader后，最后稳定了。
其他结点可能也出现类似问题，属于正常。
第六步：安装验证
可以通过ZooKeeper的脚本来查看启动状态，包括集群中各个结点的角色（或是Leader，或是Follower），如下所示，是在ZooKeeper集群中的每个结点上查询的结果：
shirdrn@zk-01:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status
JMX enabled by default
Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg
Mode: follower shirdrn@zk-02:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status
JMX enabled by default
Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg
Mode: leader shirdrn@zk-03:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status
JMX enabled by default
Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg
Mode: follower
通过上面状态查询结果可见，zk-02是集群的Leader，其余的两个结点是Follower。
另外，可以通过客户端脚本，连接到ZooKeeper集群上。对于客户端来说，ZooKeeper是一个整体（ensemble），连接到ZooKeeper集群实际上感觉在独享整个集群的服务，所以，你可以在任何一个结点上建立到服务集群的连接，例如：
shirdrn@zk-03:~/installation/zookeeper-3.3.4$ bin/zkCli.sh -server zk-01:2181
Connecting to zk-01:2181
2013-10-28 07:14:21,068 - INFO [main:Environment@97] - Client environment:zookeeper.version=3.3.3-1203054, built on 11/17/2011 05:47 GMT
2013-10-28 07:14:21,080 - INFO [main:Environment@97] - Client environment:host.name=zk-03
2013-10-28 07:14:21,085 - INFO [main:Environment@97] - Client environment:java.version=1.6.0_30
2013-10-28 07:14:21,089 - INFO [main:Environment@97] - Client environment:java.vendor=Sun Microsystems Inc.
2013-10-28 07:14:21,095 - INFO [main:Environment@97] - Client environment:java.home=/home/hadoop/installation/jdk1.6.0_30/jre
2013-10-28 07:14:21,104 - INFO [main:Environment@97] - Client environment:java.class.path=/home/hadoop/installation/zookeeper-3.3.4/bin/../build/classes:/home/hadoop/installation/zookeeper-3.3.4/bin/../build/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../zookeeper-3.3.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/log4j-1.2.15.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/jline-0.9.94.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-lang-2.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-collections-3.2.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-cli-1.1.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-tasks-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-core-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../src/java/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../conf:/home/hadoop/installation/jdk1.6.0_30/lib/*.jar:/home/hadoop/installation/jdk1.6.0_30/jre/lib/*.jar
2013-10-28 07:14:21,111 - INFO [main:Environment@97] - Client environment:java.library.path=/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib
2013-10-28 07:14:21,116 - INFO [main:Environment@97] - Client environment:java.io.tmpdir=/tmp
2013-10-28 07:14:21,124 - INFO [main:Environment@97] - Client environment:java.compiler=<NA>
2013-10-28 07:14:21,169 - INFO [main:Environment@97] - Client environment:os.name=Linux
2013-10-28 07:14:21,175 - INFO [main:Environment@97] - Client environment:os.arch=i386
2013-10-28 07:14:21,177 - INFO [main:Environment@97] - Client environment:os.version=3.0.0-14-generic
2013-10-28 07:14:21,185 - INFO [main:Environment@97] - Client environment:user.name=hadoop
2013-10-28 07:14:21,188 - INFO [main:Environment@97] - Client environment:user.home=/home/hadoop
2013-10-28 07:14:21,190 - INFO [main:Environment@97] - Client environment:user.dir=/home/hadoop/installation/zookeeper-3.3.4
2013-10-28 07:14:21,197 - INFO [main:ZooKeeper@379] - Initiating client connection, connectString=zk-01:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@bf32c
2013-10-28 07:14:21,305 - INFO [main-SendThread():ClientCnxn$SendThread@1061] - Opening socket connection to server zk-01/192.168.0.179:2181
Welcome to ZooKeeper!
2013-10-28 07:14:21,376 - INFO [main-SendThread(zk-01:2181):ClientCnxn$SendThread@950] - Socket connection established to zk-01/192.168.0.179:2181, initiating session
JLine support is enabled
[zk: zk-01:2181(CONNECTING) 0] 2013-10-28 07:14:21,872 - INFO [main-SendThread(zk-01:2181):ClientCnxn$SendThread@739] - Session establishment complete on server zk-01/192.168.0.179:2181, sessionid = 0x134bdcd6b730000, negotiated timeout = 30000 WATCHER:: WatchedEvent state:SyncConnected type:None path:null [zk: zk-01:2181(CONNECTED) 0] ls /
[zookeeper]
当前根路径为/zookeeper。
总结说明
主机名与IP地址映射配置问题 启动ZooKeeper集群时，如果ZooKeeper集群中zk-01结点的日志出现如下错误：
java.net.SocketTimeoutException
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:109)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:37:46,026 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 6400
2013-10-28 06:37:57,431 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address zk-02/202.106.199.35:3888
java.net.SocketTimeoutException
at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:109)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622)
2013-10-28 06:38:02,442 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address zk-03/202.106.199.35:3888
很显然，zk-01在启动时连接集群中其他结点（zk-02、zk-03）时，主机名映射的IP与我们实际配置的不一致，所以集群中各个结点之间无法建立链路，整个ZooKeeper集群启动是失败的。 上面错误日志中zk-02/202.106.199.35:3888实际应该是zk-02/202.192.168.0.178:3888就对了，但是在进行域名解析的时候映射有问题，修改每个结点的/etc/hosts文件，将ZooKeeper集群中所有结点主机名到IP地址的映射配置上。
参考链接
下面是我整理搜集的有关ZooKeeper相关内容的网址，可以学习参考。 中文链接：
- http://agapple.iteye.com/blog/1111377
- http://agapple.iteye.com/blog/1112032
- http://agapple.iteye.com/blog/1292129
- http://agapple.iteye.com/blog/1184023
- http://agapple.iteye.com/blog/1184040
- http://www.ibm.com/developerworks/cn/opensource/os-cn-zookeeper/
- http://luzengyi.blog.163.com/blog/static/529188201064113744373/
- http://luzengyi.blog.163.com/blog/static/529188201061155444869/
英文链接：
- http://zookeeper.apache.org/doc/trunk/zookeeperStarted.html
- http://zookeeper.apache.org/doc/r3.3.4/zookeeperOver.html
- http://zookeeper.apache.org/doc/r3.3.4/recipes.html
- http://zookeeper.apache.org/doc/trunk/
- http://wiki.apache.org/hadoop/ZooKeeper/Tutorial
- http://wiki.apache.org/hadoop/ZooKeeper/FAQ
- http://wiki.apache.org/hadoop/ZooKeeper/Troubleshooting
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