Eurosys 2011 Tutorial

Tutorial slides

• Part 1
• Part 2
• Part 3
• Part 4

Code and library

To complete this tutorial you will need the ZooKeeper 3.3.3 "fat" jar. This has all you need to run zookeeper and develop against it.

Example skeleton code:

• TaskQueueClient.java
• TaskQueueWorker.java
• TaskQueueMaster.java

Running the ZooKeeper server

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starts a ZooKeeper server running on port 2181. It is storing its data in /tmp, so this is obviously not a way you want to run in production.

Lets start up a ZooKeeper server cluster, so that we can experiment If you want to startup a cluster of server, you must do a bit more. To do this we need to create a configuration file for each server. Generally, we can share a configuration file across server, but since we are starting all three on the same machine, we need to have a configuration for each server:

...

java -jar zookeeper-3.3.3-fatjar.jar client -server 127.0.0.1:2181

_if you started up a cluster of servers, you would use 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183

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instead of just 127.0.0.1:2181.

Now lets create the znodes. We have to supply initial data for them even though it isn't used:

[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 0] create /assign ""
Created /assign
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 1] create /tasks ""
Created /tasks
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 2] ls /
[assign, tasks, zookeeper]

Tutorial slides

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Extra credit (testing)

The code you have written works and is dynamic, but doesn't handle every error correctly. Check what happens when errors occur: change the TaskQueueWorker.java to use FailFirstZooKeeper.java and see what happens. (When submitting multiple tasks you will find that one gets assigned to a phantom worker.) How do you fix it?