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From Nomar Morado <j316servi...@icloud.com>
Subject Re: observer changing to participant when there is no quorum
Date Wed, 15 Jun 2016 13:31:13 GMT
This is what I have done so far:

A,B,C are participants
C,D are observers

B,C are offline (crashed)

I am trying to:

1. Remove C, D
2. Add C,D back as participants

Will this work?

At least in my testing (might be doing wrong) I am getting this error on the first step and
hence can't get forward:

Client could not connect to rests blushed quorum: giving up after 30+ seconds

I am passing the original server configure string to zk's reconfig method.


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> On Jun 14, 2016, at 10:55 PM, Alexander Shraer <shralex@gmail.com> wrote:
> Right, a quorum of participants from the old config is required to process
> any command, including reconfig,
> and a quorum of participants from the new config is required for the
> reconfig to even start. If there's no such connected
> quorum an error NewConfigNoQuorum will be thrown.
> But there is one slightly confusing case where the error is thrown, which
> is explained in the doc: when you are
> converting an observer to a participant and there is no quorum in the new
> config without counting that "future" participant.
> So the server is connected, but since its not a participant we get the
> error above.  In that case, one first needs to
> convert the observer to remove the observer and then add it back. The
> detailed explanation is in the doc, look for
> "Changing an observer into a follower".
> On Wed, Jun 15, 2016 at 1:17 AM, Camille Fournier <camille@apache.org>
> wrote:
>> I'm finding the documentation quite confusing. I was under the impression
>> that quorum of some sort was needed to do a reconfig. Can you reconfig when
>> there is no quorum?
>> *Progress guarantees:* Up to the invocation of the reconfig operation, a
>> quorum of the old configuration is required to be available and connected
>> for ZooKeeper to be able to make progress. Once reconfig is invoked, a
>> quorum of both the old and of the new configurations must be available.
>> *Adding servers:* Before a reconfiguration is invoked, the administrator
>> must make sure that a quorum (majority) of participants from the new
>> configuration are already connected and synced with the current leader.
>> On Tue, Jun 14, 2016 at 5:35 PM, Alexander Shraer <shralex@gmail.com>
>> wrote:
>>> This is needed only in case the target config doesn't have a quorum which
>>> are already followers in the old config
>>> and are up. We need agreement from a quorum of the target config, but
>>> observers aren't participating
>>> in the voting protocol.
>>>> On Tue, Jun 14, 2016 at 7:35 PM, Michael Han <hanm@cloudera.com> wrote:
>>>> This might help:
>>>> https://zookeeper.apache.org/doc/trunk/zookeeperReconfig.html section
>>>> '*Changing
>>>> an observer into a follower:'*
>>>> "first invoke a reconfig to remove D from the configuration and then
>>> invoke
>>>> a second command to add it back as a participant (follower)."
>>>> On Tue, Jun 14, 2016 at 8:53 AM, Nomar Morado <nomar.morado@gmail.com>
>>>> wrote:
>>>>> Hi
>>>>> I was trying to promote an observer into participant when ZK loses
>>>> quorum -
>>>>> but it seems that it does not allow to.
>>>>> Would you know how this can be accomplished without having to recycle
>>> ZK?
>>>>> I am using 3.5.0-alpha
>>>>> Thanks.
>>>> --
>>>> Cheers
>>>> Michael.

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