Zookeeper

Install

Download

http://zookeeper.apache.org/releases.html

Start

$ tar -zxf zookeeper-3.4.6.tar.gz
$ cd zookeeper-3.4.6
$ vi conf/zoo.cfg

default conf

tickTime = 2000
dataDir = /path/to/zookeeper/data
clientPort = 2181
initLimit = 5
syncLimit = 2

Start

$ bin/zkServer.sh start

Start CLI

$ bin/zkCli.sh

Stop

$ bin/zkServer.sh stop

CLI

• Start znodes
• Get data
• Watch
• Set data
• Create Children / Sub-znode

Start znodes

Create
create /path /data

[zk: localhost:2181(CONNECTED) 0] create /FirstZnod "Myfirstz4zookeeper-app"
Created /FirstZnod

Create Sequential znode
create -s /path /data

[zk: localhost:2181(CONNECTED) 1] create -s /FirstZnode second-data
Created /FirstZnode0000000001

Create Ephemeral znode
create -e /path /data

[zk: localhost:2181(CONNECTED) 2] create -e /SecondZnode “Ephemeral-data”
Created /SecondZnode

=> client connection is lost => ephemeral znode will be deleted

GetData

Get data
get /path

[zk: localhost:2181(CONNECTED) 13] get /FirstZnod
Myfirstz4zookeeper-app
cZxid = 0x4
ctime = Tue Aug 21 20:42:59 KST 2018
mZxid = 0x4
mtime = Tue Aug 21 20:42:59 KST 2018
pZxid = 0x4
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 22
numChildren = 0
[zk: localhost:2181(CONNECTED) 9] get /FirstZnode0000000001
second-data
cZxid = 0x5
ctime = Tue Aug 21 20:43:25 KST 2018
mZxid = 0x5
mtime = Tue Aug 21 20:43:25 KST 2018
pZxid = 0x5
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 11
numChildren = 0
[zk: localhost:2181(CONNECTED) 10]
[zk: localhost:2181(CONNECTED) 11] get /SecondZnode
“Ephemeral-data”
cZxid = 0x6
ctime = Tue Aug 21 20:46:14 KST 2018
mZxid = 0x6
mtime = Tue Aug 21 20:46:14 KST 2018
pZxid = 0x6
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x100068ccaa10000
dataLength = 20
numChildren = 0

Watch

watch
get /path [watch] 1

[zk: localhost:2181(CONNECTED) 14] get /FirstZnod 1
Myfirstz4zookeeper-app
cZxid = 0x4
ctime = Tue Aug 21 20:42:59 KST 2018
mZxid = 0x4
mtime = Tue Aug 21 20:42:59 KST 2018
pZxid = 0x4
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 22
numChildren = 0

=> it will wait for znode changes in the background

Set data

Set data & get
set /path /data

[zk: localhost:2181(CONNECTED) 15] set /SecondZnode Data-updated
cZxid = 0x6
ctime = Tue Aug 21 20:46:14 KST 2018
mZxid = 0x7
mtime = Tue Aug 21 20:55:22 KST 2018
pZxid = 0x6
cversion = 0
dataVersion = 1
aclVersion = 0
ephemeralOwner = 0x100068ccaa10000
dataLength = 12
numChildren = 0

Create Children / Sub-znode

Create children
create /parent/path/subnode/path /data

[zk: localhost:2181(CONNECTED) 18] create /FirstZnod/Child1 firstchildren
Created /FirstZnod/Child1
[zk: localhost:2181(CONNECTED) 20] create /FirstZnod/Child2 secondchildren  
Created /FirstZnod/Child2

List children
ls /path

[zk: localhost:2181(CONNECTED) 24] ls /FirstZnod
[Child2, Child1]

Stat
stat /path

[zk: localhost:2181(CONNECTED) 25] stat /FirstZnod
cZxid = 0x4
ctime = Tue Aug 21 20:42:59 KST 2018
mZxid = 0x8
mtime = Tue Aug 21 20:56:16 KST 2018
pZxid = 0xc
cversion = 2
dataVersion = 1
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 12
numChildren = 2

Remove
rmr /path

[zk: localhost:2181(CONNECTED) 26] rmr /FirstZnod
[zk: localhost:2181(CONNECTED) 27] get /FirstZnod
Node does not exist: /FirstZnod

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How to use zookeeper in java

1. Connect to the Zookeeper ensemble.
   => assign a Session ID for the client

2. Send heartbeats to the server periodically

3. Get / Set the znodes as long as a session ID is active

4. Disconnect from the ZooKeeper ensemble, once all the tasks are completed