This document discusses ZooKeeper, an open-source server that enables distributed coordination. It provides instructions for installing ZooKeeper, describes ZooKeeper's data tree and API, and exercises for interacting with ZooKeeper including creating znodes, using watches, and setting up an ensemble across multiple servers.

1. ZooKeeper In Action
Juven Xu (许晓斌)

2. •
Apache ZooKeeper is an effort to develop and
maintain an open-source server which enables
highly reliable distributed coordination.

3. Requirements
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JDK 1.6 & JAVA_HOME
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Maven (we will need to write some java code)

4. Installation
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Download: http://zookeeper.apache.org/
releases.html
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mv conf/zoo_sample.cfg conf/zoo.cfg
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edit zoo.cfg: dataDir=/my/zk/dataDir
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bin/zkServer.sh start

5. ZooKeeper Data Tree

6. ZooKeeper API

7. bin/zkCli.sh
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zkCli.sh -server localhost:2181

8. Exercise #1
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install zookeeper, start it, and create a znode /test/
node1 with value “hello-world”

9. Problem with Polling

10. ZooKeeper Watch

11. Coding for Watch

12. Coding for Watch

13. Exercise #2
•
Write your own watch, print new value on each time
znode /test/znode1 changes

14. ZooKeeper Ensemble

15. To Setup an Ensemble
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conf/zoo.cfg: //on all servers
server.1=10.20.157.1:2888:3888
server.2=10.20.157.2:2888:3888
server.3=10.20.157.3:2888:3888
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conf/zoo.cfg: //this location is important
dataDir=/home/admin/zookeeper/zkData
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echo 1 > ${dataDir}/myid //on server.1
echo 2 > ${dataDir}/myid //on server.2
echo 3 > ${dataDir}/myid //on server.3

16. To Setup an Ensemble
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If you want to set up ensemble on one machine,
make sure these values are different:
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dataDir
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clientPort
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the ports of server.{1-5}

17. Client of a Ensemble

18. Exercise #3
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Find 2 friends, set up an Ensemble with them.
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Update your client, registering all the 3 servers.
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Kill one server, see if ensemble and client still
works
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Kill another server (now only one left), see how it
goes.