Zookeeper

1. ZooKeeper
GD

2. Outline
• Introduction
• Installation/Administering
• Recipes
• ZooKeeper internals

3. Introduction
• Originally developed at Yahoo
• Centralised coordination service, including
configuration management, election, lock, and etc
ensemble

4. Data model
• Znodes
Persistent / Ephemeral
Sequential
/app2/gd-0000000001

5. Stat structure

6. Watch
• Client registers watch in read operations
• Watches triggered by write operations
• One-time trigger

7. Outline
• Introduction
• Installation/Administering
• Recipes
• ZooKeeper internals

8. Installation
• Download http://www.gtlib.gatech.edu/pub/apache/
zookeeper/stable/
• Configure conf/zoo.cfg
tickTime=2000
dataDir=/var/lib/zookeeper
clientPort=2181
• Start
bin/zkServer.sh start
bin/zkServer.sh status

9. Cluster
• Three servers at least
• Add server list in conf/zoo.cfg and myid in dataDir
# zoo,cfg for zoo1
server.1=localhost:2666:3666
server.2=localhost:2667:3667
server.3=localhost:2668:3668
1
dataDir/myidconf/zoo.cfg

10. Administering
• bin/zkCli.sh -server
127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183
help
ls /
create /test data
get /test
set /test junk
delete /test

11. Outline
• Introduction
• Installation/Administering
• Recipes
• ZooKeeper internals

12. Queue
Put an item
1. Create a /znode /queue-A/item- with sequential flag
Pop an item
1. Get children [n,n+1,…] of /znode /queue-A
2. Delete /znode /queue-A/item-n

13. Lock
Acquire a lock
1. Create a /znode /lock/resource-m with ephemeral/sequential flag
2. Get children [n,n+1,…] of /znode /lock-
3. If /znode /lock-n is created in step 1, lock is acquired. Exit.
4. Watch /znode /lock-n (/znode /lock-(m-1)). When /znode /lock-n
deleted, go to step 2.
Release a lock
1. Delete the znode created in step 1.

14. Curator
• A high-level wrapper library
developed in Netflix originally
• Curator handles operation
retry
• Curator implements recipes

15. Outline
• Introduction
• Installation/Administering
• Recipes
• ZooKeeper internals

16. • Leader / Follower
• Quorum

17. • Epoch proposal NEWEPOCH(e): e is new epoch
• ACK-E(e_curr, hist): e_curr is current epoch of follower and
hist is current operation history
• Leader proposal NEWLEADER(e, I): I is initial state derived
from operation histories in ACK-E
ZAB

18. Reference
• http://zookeeper.apache.org/
• Apache ZooKeeper Essentials
• Zab: High-performance broadcast for primary-
backup systems