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From Jordan Zimmerman <jzimmer...@netflix.com>
Subject Re: Rolling upgrades
Date Fri, 09 Mar 2012 00:10:18 GMT
Also҆

I thought that ZK ensembles need to be odd in number. How would ZK handle
a temporary state where there is an even number?

-JZ

On 3/8/12 3:39 PM, "Alexander Shraer" <shralex@yahoo-inc.com> wrote:

>I don't think there is a problem if you do it as you say, or even if you
>just change the config files of all servers at once and restart them,
>because a majority of the new config
>necessarily intersects with a majority of the old one, so a server who
>has the latest state will be elected leader.
>
>Alex
>
>> -----Original Message-----
>> From: Jordan Zimmerman [mailto:jzimmerman@netflix.com]
>> Sent: Thursday, March 08, 2012 3:31 PM
>> To: user@zookeeper.apache.org
>> Subject: Rolling upgrades
>> 
>> I've been reading the archives regarding rolling upgrades. Here's the
>> scenario, given a stable ensemble:
>> 
>> ZK1 <-> ZK2 <-> ZK3
>> 
>> In the above, the zoo.cfg for each server looks like this (pseudo):
>> server.1=ZK1
>> server.2=ZK2
>> server.3=ZK3
>> 
>> I want to add a new server, ZK4. If I understand this correctly, I'd
>> bring up ZK4 with this config:
>> server.1=ZK1
>> server.2=ZK2
>> server.3=ZK3
>> server.4=ZK4
>> 
>> At this point, though, the configs don't match in the ensemble. How do
>> the ZK instances handle this?
>> 
>> Continuing...
>> 
>> Once ZK4 is up, ZK1 would get the new config and get restarted. Once
>> ZK1 is up, ZK2 gets new config, etc.
>> 
>> At each point of config change, the cluster is in a confused state
>> about the config. Is there code in ZK to handle this?
>> 
>> -JZ
>
>


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