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From Cee Tee <c.turks...@gmail.com>
Subject Re: About ZooKeeper Dynamic Reconfiguration
Date Wed, 21 Aug 2019 18:27:25 GMT

Yes, one side loses quorum and the other remains active. However we 
actively control which side that is, because our main application is 
active/passive with 2 datacenters. We need Zookeeper to remain active in 
the applications active datacenter.

On 21 August 2019 17:22:00 Alexander Shraer <shralex@gmail.com> wrote:
> That's great! Thanks for sharing.
>> Added benefit is that we can also control which data center gets the quorum
>> in case of a network outage between the two.
> Can you explain how this works? In case of a network outage between two 
> DCs, one of them has a quorum of participants and the other doesn't.
> The participants in the smaller set should not be operational at this time, 
> since they can't get quorum. no ?
> Thanks,
> Alex
> On Wed, Aug 21, 2019 at 7:55 AM Cee Tee <c.turksema@gmail.com> wrote:
> We have solved this by implementing a 'zookeeper cluster balancer', it
> calls the admin server api of each zookeeper to get the current status and
> will issue dynamic reconfigure commands to change dead servers into
> observers so the quorum is not in danger. Once the dead servers reconnect,
> they take the observer role and are then reconfigured into participants again.
> Added benefit is that we can also control which data center gets the quorum
> in case of a network outage between the two.
> Regards
> Chris
> On 21 August 2019 16:42:37 Alexander Shraer <shralex@gmail.com> wrote:
>> Hi,
>> Reconfiguration, as implemented, is not automatic. In your case, when
>> failures happen, this doesn't change the ensemble membership.
>> When 2 of 5 fail, this is still a minority, so everything should work
>> normally, you just won't be able to handle an additional failure. If you'd
>> like
>> to remove them from the ensemble, you need to issue an explicit
>> reconfiguration command to do so.
>> Please see details in the manual:
>> https://zookeeper.apache.org/doc/r3.5.5/zookeeperReconfig.html
>> Alex
>> On Wed, Aug 21, 2019 at 7:29 AM Gao,Wei <Wei.Gao@arcserve.com> wrote:
>>> Hi
>>>    I encounter a problem which blocks my development of load balance using
>>> ZooKeeper 3.5.5.
>>>    Actually, I have a ZooKeeper cluster which comprises of five zk
>>> servers. And the dynamic configuration file is as follows:
>>>   server.1=zk1:2888:3888:participant;
>>>   server.2=zk2:2888:3888:participant;
>>>   server.3=zk3:2888:3888:participant;
>>>   server.4=zk4:2888:3888:participant;
>>>   server.5=zk5:2888:3888:participant;
>>>   The zk cluster can work fine if every member works normally. However, if
>>> say two of them are suddenly down without previously being notified,
>>> the dynamic configuration file shown above will not be synchronized
>>> dynamically, which leads to the zk cluster fail to work normally.
>>>   I think this is a very common case which may happen at any time. If so,
>>> how can we resolve it?
>>>   Really look forward to hearing from you!
>>> Thanks

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