Zookeeper is a centralized service that helps coordinate distributed systems by providing configuration information, naming services, synchronization, and group services. It allows distributed applications to organize nodes and configuration in a filesystem-like structure and provides services like leader election, heartbeats, and atomic updates.

1. Zookeeper
What it actually is.
Tobias Schlottke
November 2011
Freitag, 2. Dezember 11

2. Zookeeper
What it actually is.
Tobias Schlottke
November 2011
Freitag, 2. Dezember 11

3. What it is
„ZooKeeper is a centralized service for maintaining
configuration information, naming, providing distributed
synchronization, and providing group services.
All of these kinds of services are used in some form or another
by distributed applications. Each time they are implemented
there is a lot of work that goes into fixing the bugs and race
conditions that are inevitable.
Because of the difficulty of implementing these kinds of
services, applications initially usually skimp on them, which
make them brittle in the presence of change and difficult to
manage. Even when done correctly, different implementations
of these services lead to management complexity when the
applications are deployed.“
Freitag, 2. Dezember 11

4. WTF?
Freitag, 2. Dezember 11

5. In simple words
„A service which helps to
coordinate distributed
systems.“
Freitag, 2. Dezember 11

6. Invented by
Freitag, 2. Dezember 11

7. Invented by
Freitag, 2. Dezember 11

8. More details please!
• Naming nodes
• Configuring nodes
• Synchronizing nodes
• Organize groups of nodes
• Heartbeat
• Democracy / Leader election
Freitag, 2. Dezember 11

9. But how to organize
this stuff?
Freitag, 2. Dezember 11

10. Filesystem Schema
application1
applicationn
application1/service1
application1/servicen
application1/service1/node0001 application1/service1/node0002
Freitag, 2. Dezember 11

11. „Filesystem“ Features
• Organized in a node tree app1/service1
• „Ephemeral“ nodes
• „Sequential“ nodes 0123
• Notification system
• High availability
• Exchange format does not matter
Freitag, 2. Dezember 11

12. Other things you get
for free
• „Atomicity“
• „Consistency“
• „Reliability“
• „Timeliness“
• „Conditional updates“ (Versioning)
Freitag, 2. Dezember 11

13. The Zookeeper Service
ZK Server 1 ZK Server 2 ZK Server N
Elected Master Slave Slave
Application 1 Application N
Freitag, 2. Dezember 11

14. The Zookeeper Service
• All Servers store a copy of data in Mem
• Master election at startup
• All updates go to the leader
• Responses are sent when a majority
persited
Freitag, 2. Dezember 11

15. Snares
• Data must fit in memory
• Data size for each node should be <1MB
• Client libraries not all that good so far
• Ephemeral nodes are not allowed to have
children
Freitag, 2. Dezember 11

16. Usecase
„I am an adserver. I deliver 20.000 ads a
second and for this, you will most likely
design me as a distributed service“
Freitag, 2. Dezember 11

17. Adserver Usecase
Database
Thrift
ZK
Coordinator
Delivery1 Delivery2 Delivery3 Delivery4
Freitag, 2. Dezember 11

18. Thats it!
Pretty simple, huh?
Freitag, 2. Dezember 11