Zookeeper 分布式服務框架是 Apache Hadoop 的一個子項目，它主要是用來解決分布式應用中經常遇到的一些數據管理問題，如：統一命名服務、狀態同步服務、集群管理、分布式應用配置項的管理等。現在openstack的項目已經有開始使用zookeeper來實現分布式開發，例如Ceilometer的Central Agent。在SDN控制器開發領域，對於控制器的高可用和負載均衡的需求也需要引用zookeeper工具。因此作為openstack架構師和開發人員，有必要深入研究zookeeper的原理和開發技巧。由於zookeeper是基於java開發項目，作為openstack的python開發語言，現在已經有一些成熟的接口api和項目，例如kazoo、tooz等。
首先我們要搭建一套zookeeper的學習研究環境
1.獲取zookeeper包
wget http://mirror.nus.edu.sg/apache/zookeeper/zookeeper-3.4.6/zookeeper-3.4.6.tar.gz
2.創建三節點環境
server1
├── data
├── dataLog
├── logs
├── zookeeper-3.4.6
└── zookeeper-3.4.6.tar.gz
server2
├── data
├── dataLog
├── logs
├── zookeeper-3.4.6
└── zookeeper-3.4.6.tar.gz
server3
├── data
├── dataLog
├── logs
├── zookeeper-3.4.6
└── zookeeper-3.4.6.tar.gz
Server主配置zoo.cfg
# 心跳間隔時間(ms)
tickTime=2000
# Follower與Leader初始化時能容忍的時間(initLimit * tickTime)
initLimit=10
# Follower與Leader請求響應時能容忍的時間(syncLimit * tickTime)
syncLimit=5
# server1數據目錄，每個server各自配置
dataDir=/path/to/server1/data
# 客戶端連接端口
clientPort=2182
# server列表:
#
# .n(標記server)=(server地址):(投票時所用端口):(選舉Leader時所用端口)
server.1=127.0.0.1:2889:3889
server.2=127.0.0.1:2990:3990
server.3=127.0.0.1:2991:3991
在每個Server/data目錄下建立一個myid文件，標識自己是哪個Server(對應zoo.cfg的server列表)
現在啟動server1
server1/zookeeper-3.4.6/bin/zkServer.sh start-foreground
#
# 輸出
2015-03-02 19:56:47,485 [myid:1] - INFO [QuorumPeer[myid=1]/0:0:0:0:0:0:0:0:2182:QuorumPeer@714] - LOOKING
2015-03-02 19:56:47,486 [myid:1] - INFO [QuorumPeer[myid=1]/0:0:0:0:0:0:0:0:2182:FastLeaderElection@815] - New election. My id = 1, proposed zxid=0x1a00000006
2015-03-02 19:56:47,488 [myid:1] - INFO [WorkerReceiver[myid=1]:FastLeaderElection@597] - Notification: 1 (message format version), 1 (n.leader), 0x1a00000006 (n.zxid), 0x1 (n.round), LOOKING (n.state), 1 (n.sid), 0x1a (n.peerEpoch) LOOKING (my state)
2015-03-02 19:56:47,510 [myid:1] - WARN [WorkerSender[myid=1]:QuorumCnxManager@382] - Cannot open channel to 2 at election address /127.0.0.1:3990
java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:345)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:368)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.toSend(QuorumCnxManager.java:341)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.process(FastLeaderElection.java:449)
at org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.run(FastLeaderElection.java:430)
at java.lang.Thread.run(Thread.java:744)
2015-03-02 19:56:47,560 [myid:1] - WARN [WorkerSender[myid=1]:QuorumCnxManager@382] - Cannot open channel to 3 at election address /127.0.0.1:3991
server1嘗試連接zoo.cfg中配置的server列表，這時server2，server3還沒啟動，因此連接失敗， 將server2，server3一並啟動后，可以看到server1已經成為Follower
2015-03-02 20:02:41,487 [myid:1] - INFO [/127.0.0.1:3889:QuorumCnxManager$Listener@511] - Received connection request /127.0.0.1:65469
2015-03-02 20:02:41,492 [myid:1] - INFO [WorkerReceiver[myid=1]:FastLeaderElection@597] - Notification: 1 (message format version), 3 (n.leader), 0x1a00000006 (n.zxid)0x1 (n.round), LOOKING (n.state), 3 (n.sid), 0x1a (n.peerEpoch) FOLLOWING (my state)
於是，可以使用客戶端嘗試連接這個集群，並且客戶端會被隨機分配到一個server
zookeeper-3.4.6/bin/zkCli.sh -server 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184
3.簡單測試
列出節點信息：
[zk: 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184(CONNECTED) 11] ls /
[dubbo, zookeeper, pampas, pubsub]
創建/workers節點：
[zk: 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184(CONNECTED) 11] create /workers ""
[zk: 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184(CONNECTED) 11] ls /
[dubbo, zookeeper, workers, pampas, pubsub]
刪除/workers節點：
[zk: 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184(CONNECTED) 11] delete /workers
[zk: localhost:2181(CONNECTED) 4] ls /
[zk: 127.0.0.1:2182,127.0.0.1:2183,127.0.0.1:2184(CONNECTED) 11]
[zk: localhost:2181(CONNECTED) 5] quit
通過以上步驟，我們就成功搭建出一套三節點zookeeper偽集群環境，為后面原理驗證和python接口開發打好基礎。