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From Rakesh R <rake...@huawei.com>
Subject RE: Electing a leader among clients
Date Thu, 07 Nov 2013 05:49:38 GMT
Another approach would be, 

Step-1) All the clients will try to create a ephemeral znode, say 'leader' under one common
path /myapp/leaderelection/ 
Step-2) Whoever succeeds will become leader and all the others will be getting KeeperException.NodeExistsException.
On this exception, clients can add a watcher to know the 'leader' znode deletion.
Step-3) On znode delete watch notification, again, this cycle continues and perform step-1.


-----Original Message-----
From: Arindam Mukherjee [mailto:arindam.mukerjee@gmail.com] 
Sent: 07 November 2013 11:09
To: user@zookeeper.apache.org
Subject: Electing a leader among clients

Using ZooKeeper I want to create a cluster of hosts where a client process on one of the hosts
can play the role of a leader or controller and coordinate tasks with processes across the
rest of the hosts. As the nodes are hosts similar, the choice of a leader can be arbitrary.
I was thinking of using ZooKeeper for this purpose.

I am very new to ZooKeeper and don't know enough of the available primitives. What would be
a good way to achieve this?

Here is one thought - please let me know if this makes sense or something else which would
work better:
1. Each ZoooKeeper client gets a monotonically increasing ID when it establishes a session
with ZooKeeper server. One way could be to create an ephemeral sequential znode and use the
assigned numeric suffix as the id - store other data in this znode.
2. Whichever client gets the lowest id becomes the leader. However, for this to work the entire
range of ids assigned to live clients at any point in time should be available to all the
clients so that each client can independently arrive at the same decision. How to do this?


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