How to setup and use zookeeper in scala using Apache Curator
source link: https://blog.knoldus.com/how-to-setup-and-use-zookeeper-in-scala-using-apache-curator/
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How to setup and use zookeeper in scala using Apache Curator
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In order to use Zookeeper to manage your project’s configurations across the cluster, first we will setup the zookeeper ensemble on our local machine (setup is for testing on a single machine) by following these steps:
1) Download a stable zookeeper release
2) Unpack it at three places and rename it to:
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/home/user/Desktop/zookeeper1,
/home/user/Desktop/zookeeper2, and
/home/user/Desktop/zookeeper3
3) In order to use zookeeper we will need to setup configuration files for all servers.
Make a new file zoo.cfg,
/home/user/Desktop/zookeeper1/conf/zoo.cfg
and add following details:
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tickTime=2000
initLimit=10
syncLimit=5
dataDir=/home/user/Desktop/zookeeperData1
clientPort=2181
server.1= localhost:2888:3888
server.2= localhost:2889:3889
server.3= localhost:2890:3890
Similarly,
/home/user/Desktop/zookeeper2/conf/zoo.cfg, as:
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tickTime=2000
initLimit=10
syncLimit=5
dataDir=/home/user/Desktop/zookeeperData2
clientPort=2182
server.1= localhost:2888:3888
server.2= localhost:2889:3889
server.3= localhost:2890:3890
And,
/home/user/Desktop/zookeeper3/conf/zoo.cfg, as:
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tickTime=2000
initLimit=10
syncLimit=5
dataDir=/home/user/Desktop/zookeeperData3
clientPort=2183
server.1= localhost:2888:3888
server.2= localhost:2889:3889
server.3= localhost:2890:3890
4) Now we will have to define each server’s id by making a new file in:
/home/user/Desktop/zookeeperData1/myid
which should have: 1
/home/user/Desktop/zookeeperData2/myid
which should have: 2
/home/user/Desktop/zookeeperData3/myid
which should have: 3
5) Next, we will start zookeeper ensemble for each server in 3 different terminals:
cd /home/user/Desktop/zookeeper1
bin/zkServer.sh start
cd /home/user/Desktop/zookeeper2
bin/zkServer.sh start
cd /home/user/Desktop/zookeeper3
bin/zkServer.sh start
6) Now we will add some data in one of the ZNode of the zookeeper ensemble by following steps:
a) bin/zkCli.sh
b) create /test_node “Some data”
7) Then we will write the following code in order to setup a watcher for zookeeper node so as to get stored data from zookeeper server using apache curator as a library to interact with our zookeeper server.
Add the following dependency in your build.sbt file:
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libraryDependencies ++= Seq(
"org.apache.curator" % "curator-framework" % "2.6.0",
"org.apache.curator" % "curator-recipes" % "2.6.0"
)
and use this to interact with the zookeeper server:
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class ZookeeperClient {
private val logger = LoggerFactory.getLogger(this.getClass.getName)
def main(args: Array[String]) = {val retryPolicy = new ExponentialBackoffRetry(1000, 3)
val curatorZookeeperClient = CuratorFrameworkFactory.newClient("localhost:2181,localhost:2182,localhost:2183", retryPolicy)curatorZookeeperClient.start
curatorZookeeperClient.getZookeeperClient.blockUntilConnectedOrTimedOut
val znodePath = "/test_node"
val originalData = new String(curatorZookeeperClient.getData.forPath(znodePath)) // This should be "Some data"
/* Zookeeper NodeCache service to get properties from ZNode */
val nodeCache = new NodeCache(curatorZookeeperClient, znodePath)
nodeCache.getListenable.addListener(new NodeCacheListener {@Override
def nodeChanged = {try {val dataFromZNode = nodeCache.getCurrentData
val newData = new String(currentData.getData) // This should be some new data after it is changed in the Zookeeper ensemble
} catch {case ex: Exception => logger.error("Exception while fetching properties from zookeeper ZNode, reason " + ex.getCause)}
}
nodeCache.start
})
}
}
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