If you're referring to my setup I explicitly don't keep the data in sync
across separate zk deployments. The logic for handling lookup to different
zk is in the client. Trying to keep data in sync across multiple
deployments of zk is probably not a great plan, but I'm sure you can think
of workarounds that will possibly address your issue if it is really
important.
On Mar 8, 2016 8:19 PM, "s influxdb" <[email protected]> wrote:
> I am referring to a set up that has different clusters
> for example 3 zk cluster
> cluster ABC DC1 { node 1, node 2 } DC 2 { node 3 , node 4 } DC 3 { node 5}
> cluster DEF DC2 { node 6, node 7 } DC 1 { node 8 , node 9 } DC 3 { node
> 10}
> cluster GHI DC3 { node 11, node 12 } DC 2 { node 13 , node 14 } DC 1 {
> node 15}
>
> This survives any single DC being unavailable.
>
> My question was how is the data kept in sync among the 3 different zk
> clusters. for example between cluster ABC and DEF.
> and how is the client failing over to DEF when ABC is unavailable
>
>
>
>
> On Tue, Mar 8, 2016 at 4:10 PM, Shawn Heisey <[email protected]> wrote:
>
> > On 3/8/2016 3:40 PM, s influxdb wrote:
> > > How does the client failover to the DC2 if DC1 is down ? Does the
> > services
> > > registered on DC1 for example with ephemeral nodes have to re-register
> > with
> > > DC2 ?
> >
> > Even though Flavio and Camille have both said this, I'm not sure whether
> > the posters on this thread are hearing it:
> >
> > If you only have two datacenters, you cannot set up a reliable zookeeper
> > ensemble. It's simply not possible. There are NO combinations of
> > servers that will achieve fault tolerance with only two datacenters.
> >
> > The reason this won't work is the same reason that you cannot set up a
> > reliable ensemble with only two servers. If either data center goes
> > down, half of your ZK nodes will be gone, and neither data center will
> > have enough nodes to achieve quorum.
> >
> > When you have three datacenters that are all capable of directly
> > reaching each other, you only need one ZK node in each location. If any
> > single DC goes down, the other two will be able to keep the ensemble
> > running.
> >
> > Data is replicated among the DCs in exactly the same way that it is if
> > all the servers are in one place. I don't know enough about internal ZK
> > operation to comment further.
> >
> > =============
> >
> > Some TL;DR information to follow:
> >
> > If you want to be able to take a node down for maintenance in a multi-DC
> > situation and *still* survive an entire DC going down, you need three
> > nodes in each of three data centers -- nine total. This ensemble is
> > able to survive any four servers going down, so you can take down a node
> > in one DC for maintenance, and if one of the other DCs fails entirely,
> > there will be five functioning servers that can maintain quorum.
> >
> > Detailed information for the specific situation outlined by Kaushal:
> >
> > DC-1 1 Leader 2 Followers
> > DC-2 1 Follower 2 Observers.
> >
> > A six-node ensemble requires at least operational four nodes to maintain
> > quorum. If either of those data centers fails, there are only three
> > nodes left, which is not enough.
> >
> > Thanks,
> > Shawn
> >
> >
>
