you and ted are correct. the id gives zookeeper a stable identifier to use even if the ip address changes. if the ip address doesn't change, we could use that, but we didn't want to make that a built in assumption. if you really do have a rock solid ip address, you could make a wrapper startup script that starts up and creates the myid file based on the ip address. i gotta say though, i've found that such assumptions are often found to be invalid.

ben

Eric Bowman wrote:
Another way of doing it, though, would be to tell each instance which IP
to use at startup.

That way the config can be identical for all users, and there can be
whatever logic is required to figure out the right IP address, in the
place where logic executing anyhow.

I do agree that maintaining the myid file is ackward compared to other
approaches that are working elsewhere.  It's not really clear what
purpose the my id serves except to bind an ip address to a running instance.

cheers,
Eric

Ted Dunning wrote:
A server doesn't have a unique IP address.

Each interface can have 1 or more IP addresses and there can be many
interfaces.  Furthermore, an IP address can move from one machine to
another.

2009/9/25 Ørjan Horpestad <orj...@gmail.com>

Hi Ben

Well, im just wondering why the server's own unique IP-address isn't
good enough as a valid identifyer; it strikes me to be a bit
exhausting to manually set the id for each server in the cluster. Or
maybe there is some details im not getting here  :-)

Regards, Orjan

On Fri, Sep 25, 2009 at 3:56 PM, Benjamin Reed <br...@yahoo-inc.com>
wrote:
can you clarify what you are asking for? are you just looking for
motivation? or are you trying to find out how to use it?

the myid file just has the unique identifier (number) of the server in
the
cluster. that number is matched against the id in the configuration file.
there isn't much to say about it:
http://hadoop.apache.org/zookeeper/docs/r3.2.1/zookeeperStarted.html

ben

Ørjan Horpestad wrote:
Hi!
Can someone pin-point me to a site (or please explain ) where I can
read about the use of the myid-file for configuring the id of the
ZooKeeper servers?
I'm sure there is a good reason for using this approach, but it is the
first time I have come over this type of non-automatic way for
administrating replicas.

Regards, Orjan





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