[openstack-dev] [Cinder] A possible solution for HA Active-Active

Joshua Harlow harlowja at outlook.com
Fri Jul 31 15:56:54 UTC 2015

Mike Perez wrote:
> On Mon, Jul 27, 2015 at 12:35 PM, Gorka Eguileor<geguileo at redhat.com>  wrote:
>> I know we've all been looking at the HA Active-Active problem in Cinder
>> and trying our best to figure out possible solutions to the different
>> issues, and since current plan is going to take a while (because it
>> requires that we finish first fixing Cinder-Nova interactions), I've been
>> looking at alternatives that allow Active-Active configurations without
>> needing to wait for those changes to take effect.
>> And I think I have found a possible solution, but since the HA A-A
>> problem has a lot of moving parts I ended up upgrading my initial
>> Etherpad notes to a post [1].
>> Even if we decide that this is not the way to go, which we'll probably
>> do, I still think that the post brings a little clarity on all the
>> moving parts of the problem, even some that are not reflected on our
>> Etherpad [2], and it can help us not miss anything when deciding on a
>> different solution.
> Based on IRC conversations in the Cinder room and hearing people's
> opinions in the spec reviews, I'm not convinced the complexity that a
> distributed lock manager adds to Cinder for both developers and the
> operators who ultimately are going to have to learn to maintain things
> like Zoo Keeper as a result is worth it.
> **Key point**: We're not scaling Cinder itself, it's about scaling to
> avoid build up of operations from the storage backend solutions
> themselves.
> Whatever people think ZooKeeper "scaling level" is going to accomplish
> is not even a question. We don't need it, because Cinder isn't as
> complex as people are making it.

I agree with 'cinder isn't as complex as people are making it' and that 
is very likely a good thing to keep in mind, whether zookeeper can help 
or not is a different question. Zookeeper imho is just another tool in 
your toolset/belt, and as with any tool u have to know when to use it 
(of course you can also just continue using chisels and such to); I'd 
rather people see that it is just that and avoid getting caught up on 
the other aspects prematurely.

...random thought here, skip as needed... in all honesty orchestration 
solutions like mesos 
map-reduce solutions like hadoop, stream processing systems like apache 
storm (...), are already using zookeeper and I'm not saying we should 
just use it cause they are, but the likelihood that they just picked it 
for no reason are imho slim.

> I'd like to think the Cinder team is a great in recognizing potential
> cross project initiatives. Look at what Thang Pham has done with
> Nova's version object solution. He made a generic solution into an
> Oslo solution for all, and Cinder is using it. That was awesome, and
> people really appreciated that there was a focus for other projects to
> get better, not just Cinder.
> Have people consider Ironic's hash ring solution? The project Akanda
> is now adopting it [1], and I think it might have potential. I'd
> appreciate it if interested parties could have this evaluated before
> the Cinder midcycle sprint next week, to be ready for discussion.
> [1] - https://review.openstack.org/#/c/195366/
> --
> Mike Perez
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