[ClusterLabs] Pacemaker with Zookeeper??

Ken Gaillot kgaillot at redhat.com
Tue May 17 11:06:09 EDT 2016

On 05/17/2016 09:54 AM, Digimer wrote:
> On 16/05/16 04:35 AM, Bogdan Dobrelya wrote:
>> On 05/16/2016 09:23 AM, Jan Friesse wrote:
>>>> Hi,
>>>> I have an idea: use Pacemaker with Zookeeper (instead of Corosync). Is
>>>> it possible?
>>>> Is there any examination about that?
>> Indeed, would be *great* to have a Pacemaker based control plane on top
>> of other "pluggable" distributed KVS & messaging systems, for example
>> etcd as well :)
>> I'm looking forward to joining any dev efforts around that, although I'm
>> not a Java or Go developer.
> Part of open source is the freedom to do whatever you want, of course.
> Let me ask though; What problems would zookeeper, etcd or other systems
> solve that can't be solved in corosync?
> I ask because the HA community just finished a multi-year effort to
> merge different projects into one common HA stack. This has a lot of
> benefits to the user base, not least of which is lack of confusion.
> Strikes me that the significant time investment in supporting a new
> comms layer would be much more beneficially spent on improving the
> existing stack.
> Again, anyone is free to do whatever they want... I just don't see the
> motivator personally.
> digimer

I see one big difference that is both a strength and a weakness: these
other packages have a much wider user base beyond the HA cluster use
case. The strength is that there will be many more developers working to
fix bugs, add features, etc. The weakness is that most of those
developers are ignorant of HA clustering and could easily cause more
problems for the HA use case than they fix.

Another potential benefit is the familiarity factor -- people are more
comfortable with things they recognize from somewhere else. So it might
help Pacemaker adoption, especially in the communities that already use
these packages.

I'm not aware of any technical advantages, and I wouldn't expect any,
given corosync's long HA focus.

>>> From my point of view (and yes, I'm biased), biggest problem of Zookeper
>>> is need to have quorum
>>> (https://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html#sc_designing).
>>> Direct consequence is inability to tolerate one node failure in 2 node
>>> cluster -> no 2 node clusters (and such deployment is extremely
>>> popular). Also Corosync can operate completely without quorum.
>>> Regards,
>>>   Honza
>>>> Thanks for your help!
>>>> Hai Nguyen

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