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From Benjamin Reed <br...@yahoo-inc.com>
Subject Re: The idea behind 'myid'
Date Fri, 25 Sep 2009 16:30:17 GMT
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 <orjanh@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 <breed@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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