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Zookeeper, mail # user - Can Observers be reconfigured in a DR situation?


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Re: Can Observers be reconfigured in a DR situation?
César Álvarez Núñez 2012-07-10, 14:54
I've changed a server from Observer to Leader under a similar scenario
(data migration form old DC to new DC) without any problem. Just stop all
servers, change the configuration and start up all servers. Everything
should work fine.
/César.

On Tue, Jul 10, 2012 at 4:40 PM, Raj N <[EMAIL PROTECTED]> wrote:

> I am purely talking about a DR scenario. As in we can safely assume that
> the primary DC is no longer available. Also before the DR, the clients were
> connecting to the ZK ensemble in primary and after the DR they will connect
> to the ZK ensemble in secondary DC. You wont have a split brain problem.
> The only problem I see is potential loss of some data. The question really
> was if there are any gotchas in reconfiguring a Zookeeper node which was a
> observer to now be a leader/follower.
>
> Thanks
> -Raj
>
> On Tue, Jul 10, 2012 at 6:31 AM, David Nickerson <
> [EMAIL PROTECTED]> wrote:
>
> > Hi Raj,
> >
> > I've been considering this same solution for my project. Let's say that
> the
> > secondary DC automatically makes its own quorum when it can no-longer see
> > the primary. Then you have a case where a network partition can result in
> > your quorum splitting into two autonomously running quorums. (ZooKeeper's
> > majority rule exists to prevent this situation.) Just make sure that you
> > have some additional logic that invalidates the primary once it can
> > no-longer be found.
> >
> > On Tue, Jul 10, 2012 at 3:39 AM, César Álvarez Núñez <
> > [EMAIL PROTECTED]> wrote:
> >
> > > Yes you can. Just edit the zoo.cfg from the  backup DC, comment the
> lines
> > > relative to the nodes in the primary DC and the observer peer type.
> > >
> > > In this way you can start a new ZK ensemble with just the 3 servers on
> > > backup DC.
> > >
> > > But be aware that due to latency issues the backup DC could not have
> the
> > > latest changes from the active DC.
> > >
> > > You will also need to update each client "connection string" to use
> only
> > > the servers from the backup DC.
> > >
> > > /Sent from my GP0.
> > > El 09/07/2012 23:16, "Raj N" <[EMAIL PROTECTED]> escribió:
> > >
> > > > Let's say you have 2 DCs, primary and secondary. The primary DC has
> a 3
> > > > node zookeeper quorum. And the secondary DC has 3 nodes that are
> > > observers.
> > > > Is it possible in a DR scenario(primary down) to make the 3 observer
> > > nodes
> > > > the new quorum?
> > > >
> > > > Thanks
> > > > -Raj
> > > >
> > >
> >
>